<ol>
<li><a href="#stack">The Stack</a>
<li><a href="#punctuation">Punctuation</a>
+ <li><a href="#comments">Comments</a>
<li><a href="#literals">Literals</a>
<li><a href="#words">Words</a>
+ <li><a href="style">Standard Style</a>
<li><a href="#builtins">Built-Ins</a>
</ol>
</li>
<li><a href="#runtime">The Runtime</a></li>
<li><a href="#driver">Compiler Driver</a></li>
<li><a href="#tests">Test Programs</a></li>
+ <li><a href="#exercise">Exercise</a></li>
+ <li><a href="#todo">Things Remaining To Be Done</a></li>
</ol>
</li>
</ol>
<div class="doc_text">
<p>This document is another way to learn about LLVM. Unlike the
<a href="LangRef.html">LLVM Reference Manual</a> or
-<a href="ProgrammersManual.html">LLVM Programmer's Manual</a>, this
-document walks you through the implementation of a programming language
-named Stacker. Stacker was invented specifically as a demonstration of
+<a href="ProgrammersManual.html">LLVM Programmer's Manual</a>, here we learn
+about LLVM through the experience of creating a simple programming language
+named Stacker. Stacker was invented specifically as a demonstration of
LLVM. The emphasis in this document is not on describing the
-intricacies of LLVM itself, but on how to use it to build your own
+intricacies of LLVM itself but on how to use it to build your own
compiler system.</p>
</div>
<!-- ======================================================================= -->
<p>Amongst other things, LLVM is a platform for compiler writers.
Because of its exceptionally clean and small IR (intermediate
representation), compiler writing with LLVM is much easier than with
-other system. As proof, the author of Stacker wrote the entire
-compiler (language definition, lexer, parser, code generator, etc.) in
-about <em>four days</em>! That's important to know because it shows
-how quickly you can get a new
-language up when using LLVM. Furthermore, this was the <em >first</em>
+other system. As proof, I wrote the entire compiler (language definition,
+lexer, parser, code generator, etc.) in about <em>four days</em>!
+That's important to know because it shows how quickly you can get a new
+language running when using LLVM. Furthermore, this was the <em >first</em>
language the author ever created using LLVM. The learning curve is
included in that four days.</p>
<p>The language described here, Stacker, is Forth-like. Programs
-are simple collections of word definitions and the only thing definitions
+are simple collections of word definitions, and the only thing definitions
can do is manipulate a stack or generate I/O. Stacker is not a "real"
-programming language; its very simple. Although it is computationally
+programming language; it's very simple. Although it is computationally
complete, you wouldn't use it for your next big project. However,
-the fact that it is complete, its simple, and it <em>doesn't</em> have
+the fact that it is complete, it's simple, and it <em>doesn't</em> have
a C-like syntax make it useful for demonstration purposes. It shows
-that LLVM could be applied to a wide variety of language syntaxes.</p>
+that LLVM could be applied to a wide variety of languages.</p>
<p>The basic notions behind stacker is very simple. There's a stack of
integers (or character pointers) that the program manipulates. Pretty
much the only thing the program can do is manipulate the stack and do
: MAIN hello_world ;<br></code></p>
<p>This has two "definitions" (Stacker manipulates words, not
functions and words have definitions): <code>MAIN</code> and <code>
-hello_world</code>. The <code>MAIN</code> definition is standard, it
+hello_world</code>. The <code>MAIN</code> definition is standard; it
tells Stacker where to start. Here, <code>MAIN</code> is defined to
simply invoke the word <code>hello_world</code>. The
<code>hello_world</code> definition tells stacker to push the
-<code>"Hello, World!"</code> string onto the stack, print it out
+<code>"Hello, World!"</code> string on to the stack, print it out
(<code>>s</code>), pop it off the stack (<code>DROP</code>), and
finally print a carriage return (<code>CR</code>). Although
<code>hello_world</code> uses the stack, its net effect is null. Well
<!-- ======================================================================= -->
<div class="doc_section"><a name="lessons"></a>Lessons I Learned About LLVM</div>
<div class="doc_text">
-<p>Stacker was written for two purposes: (a) to get the author over the
-learning curve and (b) to provide a simple example of how to write a compiler
-using LLVM. During the development of Stacker, many lessons about LLVM were
+<p>Stacker was written for two purposes: </p>
+<ol>
+ <li>to get the author over the learning curve, and</li>
+ <li>to provide a simple example of how to write a compiler using LLVM.</li>
+</ol>
+<p>During the development of Stacker, many lessons about LLVM were
learned. Those lessons are described in the following subsections.<p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="value"></a>Everything's a Value!</div>
<div class="doc_text">
-<p>Although I knew that LLVM used a Single Static Assignment (SSA) format,
+<p>Although I knew that LLVM uses a Single Static Assignment (SSA) format,
it wasn't obvious to me how prevalent this idea was in LLVM until I really
-started using it. Reading the Programmer's Manual and Language Reference I
-noted that most of the important LLVM IR (Intermediate Representation) C++
+started using it. Reading the <a href="ProgrammersManual.html">
+Programmer's Manual</a> and <a href="LangRef.html">Language Reference</a>,
+I noted that most of the important LLVM IR (Intermediate Representation) C++
classes were derived from the Value class. The full power of that simple
design only became fully understood once I started constructing executable
expressions for Stacker.</p>
<p>This really makes your programming go faster. Think about compiling code
-for the following C/C++ expression: (a|b)*((x+1)/(y+1)). You could write a
-function using LLVM that does exactly that, this way:</p>
+for the following C/C++ expression: <code>(a|b)*((x+1)/(y+1))</code>. Assuming
+the values are on the stack in the order a, b, x, y, this could be
+expressed in stacker as: <code>1 + SWAP 1 + / ROT2 OR *</code>.
+You could write a function using LLVM that computes this expression like this: </p>
<pre><code>
Value*
-expression(BasicBlock*bb, Value* a, Value* b, Value* x, Value* y )
+expression(BasicBlock* bb, Value* a, Value* b, Value* x, Value* y )
{
Instruction* tail = bb->getTerminator();
ConstantSInt* one = ConstantSInt::get( Type::IntTy, 1);
BinaryOperator* or1 =
- new BinaryOperator::create( Instruction::Or, a, b, "", tail );
+ BinaryOperator::create( Instruction::Or, a, b, "", tail );
BinaryOperator* add1 =
- new BinaryOperator::create( Instruction::Add, x, one, "", tail );
+ BinaryOperator::create( Instruction::Add, x, one, "", tail );
BinaryOperator* add2 =
- new BinaryOperator::create( Instruction::Add, y, one, "", tail );
+ BinaryOperator::create( Instruction::Add, y, one, "", tail );
BinaryOperator* div1 =
- new BinaryOperator::create( Instruction::Div, add1, add2, "", tail);
+ BinaryOperator::create( Instruction::Div, add1, add2, "", tail);
BinaryOperator* mult1 =
- new BinaryOperator::create( Instruction::Mul, or1, div1, "", tail );
+ BinaryOperator::create( Instruction::Mul, or1, div1, "", tail );
return mult1;
}
</code></pre>
-<p>"Okay, big deal," you say. It is a big deal. Here's why. Note that I didn't
+<p>"Okay, big deal," you say? It is a big deal. Here's why. Note that I didn't
have to tell this function which kinds of Values are being passed in. They could be
-instructions, Constants, Global Variables, etc. Furthermore, if you specify Values
-that are incorrect for this sequence of operations, LLVM will either notice right
-away (at compilation time) or the LLVM Verifier will pick up the inconsistency
-when the compiler runs. In no case will you make a type error that gets passed
-through to the generated program. This <em>really</em> helps you write a compiler
-that always generates correct code!<p>
+<code>Instruction</code>s, <code>Constant</code>s, <code>GlobalVariable</code>s, or
+any of the other subclasses of <code>Value</code> that LLVM supports.
+Furthermore, if you specify Values that are incorrect for this sequence of
+operations, LLVM will either notice right away (at compilation time) or the LLVM
+Verifier will pick up the inconsistency when the compiler runs. In either case
+LLVM prevents you from making a type error that gets passed through to the
+generated program. This <em>really</em> helps you write a compiler that
+always generates correct code!<p>
<p>The second point is that we don't have to worry about branching, registers,
stack variables, saving partial results, etc. The instructions we create
<em>are</em> the values we use. Note that all that was created in the above
code is a Constant value and five operators. Each of the instructions <em>is</em>
-the resulting value of that instruction.</p>
+the resulting value of that instruction. This saves a lot of time.</p>
<p>The lesson is this: <em>SSA form is very powerful: there is no difference
- between a value and the instruction that created it.</em> This is fully
+between a value and the instruction that created it.</em> This is fully
enforced by the LLVM IR. Use it to your best advantage.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="blocks"></a>Concrete Blocks</div>
<div class="doc_text">
<p>After a little initial fumbling around, I quickly caught on to how blocks
-should be constructed. The use of the standard template library really helps
-simply the interface. In general, here's what I learned:
+should be constructed. In general, here's what I learned:
<ol>
<li><em>Create your blocks early.</em> While writing your compiler, you
will encounter several situations where you know apriori that you will
- need several blocks. For example, if-then-else, switch, while and for
+ need several blocks. For example, if-then-else, switch, while, and for
statements in C/C++ all need multiple blocks for expression in LVVM.
The rule is, create them early.</li>
<li><em>Terminate your blocks early.</em> This just reduces the chances
<code>getTerminator()</code> method on a <code>BasicBlock</code>), it can
always be used as the <code>insert_before</code> argument to your instruction
constructors. This causes the instruction to automatically be inserted in
- the RightPlace&tm; place, just before the terminating instruction. The
+ the RightPlace™ place, just before the terminating instruction. The
nice thing about this design is that you can pass blocks around and insert
- new instructions into them without ever known what instructions came
+ new instructions into them without ever knowing what instructions came
before. This makes for some very clean compiler design.</li>
</ol>
<p>The foregoing is such an important principal, its worth making an idiom:</p>
-<pre>
-<code>
+<pre><code>
BasicBlock* bb = new BasicBlock();</li>
bb->getInstList().push_back( new Branch( ... ) );
new Instruction(..., bb->getTerminator() );
-</code>
-</pre>
+</code></pre>
<p>To make this clear, consider the typical if-then-else statement
(see StackerCompiler::handle_if() method). We can set this up
in a single function using LLVM in the following way: </p>
MyCompiler::handle_if( BasicBlock* bb, SetCondInst* condition )
{
// Create the blocks to contain code in the structure of if/then/else
- BasicBlock* then = new BasicBlock();
- BasicBlock* else = new BasicBlock();
- BasicBlock* exit = new BasicBlock();
+ BasicBlock* then_bb = new BasicBlock();
+ BasicBlock* else_bb = new BasicBlock();
+ BasicBlock* exit_bb = new BasicBlock();
// Insert the branch instruction for the "if"
- bb->getInstList().push_back( new BranchInst( then, else, condition ) );
+ bb->getInstList().push_back( new BranchInst( then_bb, else_bb, condition ) );
// Set up the terminating instructions
- then->getInstList().push_back( new BranchInst( exit ) );
- else->getInstList().push_back( new BranchInst( exit ) );
+ then->getInstList().push_back( new BranchInst( exit_bb ) );
+ else->getInstList().push_back( new BranchInst( exit_bb ) );
// Fill in the then part .. details excised for brevity
- this->fill_in( then );
+ this->fill_in( then_bb );
// Fill in the else part .. details excised for brevity
- this->fill_in( else );
+ this->fill_in( else_bb );
// Return a block to the caller that can be filled in with the code
// that follows the if/then/else construct.
- return exit;
+ return exit_bb;
}
</pre>
<p>Presumably in the foregoing, the calls to the "fill_in" method would add
the instructions for the "then" and "else" parts. They would use the third part
of the idiom almost exclusively (inserting new instructions before the
terminator). Furthermore, they could even recurse back to <code>handle_if</code>
-should they encounter another if/then/else statement and it will all "just work".
-<p>
+should they encounter another if/then/else statement, and it will just work.</p>
<p>Note how cleanly this all works out. In particular, the push_back methods on
the <code>BasicBlock</code>'s instruction list. These are lists of type
-<code>Instruction</code> which also happen to be <code>Value</code>s. To create
+<code>Instruction</code> (which is also of type <code>Value</code>). To create
the "if" branch we merely instantiate a <code>BranchInst</code> that takes as
-arguments the blocks to branch to and the condition to branch on. The blocks
-act like branch labels! This new <code>BranchInst</code> terminates
-the <code>BasicBlock</code> provided as an argument. To give the caller a way
-to keep inserting after calling <code>handle_if</code> we create an "exit" block
-which is returned to the caller. Note that the "exit" block is used as the
-terminator for both the "then" and the "else" blocks. This gaurantees that no
-matter what else "handle_if" or "fill_in" does, they end up at the "exit" block.
+arguments the blocks to branch to and the condition to branch on. The
+<code>BasicBlock</code> objects act like branch labels! This new
+<code>BranchInst</code> terminates the <code>BasicBlock</code> provided
+as an argument. To give the caller a way to keep inserting after calling
+<code>handle_if</code>, we create an <code>exit_bb</code> block which is
+returned
+to the caller. Note that the <code>exit_bb</code> block is used as the
+terminator for both the <code>then_bb</code> and the <code>else_bb</code>
+blocks. This guarantees that no matter what else <code>handle_if</code>
+or <code>fill_in</code> does, they end up at the <code>exit_bb</code> block.
</p>
</div>
<!-- ======================================================================= -->
method on the various lists. This is so common that it is worth mentioning.
The "push_back" inserts a value into an STL list, vector, array, etc. at the
end. The method might have also been named "insert_tail" or "append".
-Althought I've used STL quite frequently, my use of push_back wasn't very
+Although I've used STL quite frequently, my use of push_back wasn't very
high in other programs. In LLVM, you'll use it all the time.
</p>
</div>
<div class="doc_text">
<p>
It took a little getting used to and several rounds of postings to the LLVM
-mail list to wrap my head around this instruction correctly. Even though I had
+mailing list to wrap my head around this instruction correctly. Even though I had
read the Language Reference and Programmer's Manual a couple times each, I still
missed a few <em>very</em> key points:
</p>
<ul>
- <li>GetElementPtrInst gives you back a Value for the last thing indexed</em>
+ <li>GetElementPtrInst gives you back a Value for the last thing indexed.</em>
<li>All global variables in LLVM are <em>pointers</em>.
<li>Pointers must also be dereferenced with the GetElementPtrInst instruction.
</ul>
<p>This means that when you look up an element in the global variable (assuming
-its a struct or array), you <em>must</em> deference the pointer first! For many
+it's a struct or array), you <em>must</em> deference the pointer first! For many
things, this leads to the idiom:
</p>
<pre><code>
will run against your grain because you'll naturally think of the global array
variable and the address of its first element as the same. That tripped me up
for a while until I realized that they really do differ .. by <em>type</em>.
-Remember that LLVM is a strongly typed language itself. Absolutely everything
-has a type. The "type" of the global variable is [24 x int]*. That is, its
+Remember that LLVM is strongly typed. Everything has a type.
+The "type" of the global variable is [24 x int]*. That is, it's
a pointer to an array of 24 ints. When you dereference that global variable with
-a single index, you now have a " [24 x int]" type, the pointer is gone. Although
+a single (0) index, you now have a "[24 x int]" type. Although
the pointer value of the dereferenced global and the address of the zero'th element
in the array will be the same, they differ in their type. The zero'th element has
type "int" while the pointer value has type "[24 x int]".</p>
-<p>Get this one aspect of LLVM right in your head and you'll save yourself
+<p>Get this one aspect of LLVM right in your head, and you'll save yourself
a lot of compiler writing headaches down the road.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="linkage"></a>Getting Linkage Types Right</div>
<div class="doc_text">
<p>Linkage types in LLVM can be a little confusing, especially if your compiler
-writing mind has affixed very hard concepts to particular words like "weak",
+writing mind has affixed firm concepts to particular words like "weak",
"external", "global", "linkonce", etc. LLVM does <em>not</em> use the precise
-definitions of say ELF or GCC even though they share common terms. To be fair,
+definitions of, say, ELF or GCC, even though they share common terms. To be fair,
the concepts are related and similar but not precisely the same. This can lead
you to think you know what a linkage type represents but in fact it is slightly
different. I recommend you read the
<a href="LangRef.html#linkage"> Language Reference on this topic</a> very
-carefully.<p>
+carefully.
Then, read it again.<p>
<p>Here are some handy tips that I discovered along the way:</p>
<ul>
- <li>Unitialized means external. That is, the symbol is declared in the current
- module and can be used by that module but it is not defined by that module.</li>
- <li>Setting an initializer changes a global's linkage type from whatever it was
- to a normal, defind global (not external). You'll need to call the setLinkage()
- method to reset it if you specify the initializer after the GlobalValue has been
- constructed. This is important for LinkOnce and Weak linkage types.</li>
- <li>Appending linkage can be used to keep track of compilation information at
- runtime. It could be used, for example, to build a full table of all the C++
- virtual tables or hold the C++ RTTI data, or whatever. Appending linkage can
- only be applied to arrays. The arrays are concatenated together at link time.</li>
+ <li><em>Uninitialized means external.</em> That is, the symbol is declared in the current
+ module and can be used by that module, but it is not defined by that module.</li>
+ <li><em>Setting an initializer changes a global' linkage type.</em> Setting an
+ initializer changes a global's linkage type from whatever it was to a normal,
+ defined global (not external). You'll need to call the setLinkage() method to
+ reset it if you specify the initializer after the GlobalValue has been constructed.
+ This is important for LinkOnce and Weak linkage types.</li>
+ <li><em>Appending linkage can keep track of things.</em> Appending linkage can
+ be used to keep track of compilation information at runtime. It could be used,
+ for example, to build a full table of all the C++ virtual tables or hold the
+ C++ RTTI data, or whatever. Appending linkage can only be applied to arrays.
+ All arrays with the same name in each module are concatenated together at link
+ time.</li>
</ul>
</div>
<!-- ======================================================================= -->
functions in the LLVM IR that make things easier. Here's what I learned: </p>
<ul>
<li>Constants are Values like anything else and can be operands of instructions</li>
- <li>Integer constants, frequently needed can be created using the static "get"
+ <li>Integer constants, frequently needed, can be created using the static "get"
methods of the ConstantInt, ConstantSInt, and ConstantUInt classes. The nice thing
about these is that you can "get" any kind of integer quickly.</li>
<li>There's a special method on Constant class which allows you to get the null
</div>
<!-- ======================================================================= -->
<div class="doc_section"> <a name="lexicon">The Stacker Lexicon</a></div>
+<div class="doc_text"><p>This section describes the Stacker language</p></div>
<div class="doc_subsection"><a name="stack"></a>The Stack</div>
<div class="doc_text">
<p>Stacker definitions define what they do to the global stack. Before
proceeding, a few words about the stack are in order. The stack is simply
a global array of 32-bit integers or pointers. A global index keeps track
-of the location of the to of the stack. All of this is hidden from the
-programmer but it needs to be noted because it is the foundation of the
+of the location of the top of the stack. All of this is hidden from the
+programmer, but it needs to be noted because it is the foundation of the
conceptual programming model for Stacker. When you write a definition,
you are, essentially, saying how you want that definition to manipulate
the global stack.</p>
<p>Manipulating the stack can be quite hazardous. There is no distinction
given and no checking for the various types of values that can be placed
on the stack. Automatic coercion between types is performed. In many
-cases this is useful. For example, a boolean value placed on the stack
+cases, this is useful. For example, a boolean value placed on the stack
can be interpreted as an integer with good results. However, using a
word that interprets that boolean value as a pointer to a string to
print out will almost always yield a crash. Stacker simply leaves it
to the programmer to get it right without any interference or hindering
-on interpretation of the stack values. You've been warned :) </p>
+on interpretation of the stack values. You've been warned. :) </p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="punctuation"></a>Punctuation</div>
characters are used to introduce and terminate a definition
(respectively). Except for <em>FORWARD</em> declarations, definitions
are all you can specify in Stacker. Definitions are read left to right.
-Immediately after the semi-colon comes the name of the word being defined.
-The remaining words in the definition specify what the word does.</p>
+Immediately after the colon comes the name of the word being defined.
+The remaining words in the definition specify what the word does. The definition
+is terminated by a semi-colon.</p>
+<p>So, your typical definition will have the form:</p>
+<pre><code>: name ... ;</code></pre>
+<p>The <code>name</code> is up to you but it must start with a letter and contain
+only letters, numbers, and underscore. Names are case sensitive and must not be
+the same as the name of a built-in word. The <code>...</code> is replaced by
+the stack manipulating words that you wish to define <code>name</code> as. <p>
+</div>
+<!-- ======================================================================= -->
+<div class="doc_subsection"><a name="comments"></a>Comments</div>
+<div class="doc_text">
+ <p>Stacker supports two types of comments. A hash mark (#) starts a comment
+ that extends to the end of the line. It is identical to the kind of comments
+ commonly used in shell scripts. A pair of parentheses also surround a comment.
+ In both cases, the content of the comment is ignored by the Stacker compiler. The
+ following does nothing in Stacker.
+ </p>
+<pre><code>
+# This is a comment to end of line
+( This is an enclosed comment )
+</code></pre>
+<p>See the <a href="#example">example</a> program to see comments in use in
+a real program.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="literals"></a>Literals</div>
<div class="doc_text">
- <p>There are three kinds of literal values in Stacker. Integer, Strings,
+ <p>There are three kinds of literal values in Stacker: Integers, Strings,
and Booleans. In each case, the stack operation is to simply push the
- value onto the stack. So, for example:<br/>
+ value on to the stack. So, for example:<br/>
<code> 42 " is the answer." TRUE </code><br/>
- will push three values onto the stack: the integer 42, the
- string " is the answer." and the boolean TRUE.</p>
+ will push three values on to the stack: the integer 42, the
+ string " is the answer.", and the boolean TRUE.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="words"></a>Words</div>
transformation he applies will affect the program.</p>
<p>Words in a definition come in two flavors: built-in and programmer
defined. Simply mentioning the name of a previously defined or declared
-programmer-defined word causes that words definition to be invoked. It
+programmer-defined word causes that word's stack actions to be invoked. It
is somewhat like a function call in other languages. The built-in
-words have various effects, described below.</p>
+words have various effects, described <a href="#builtins">below</a>.</p>
<p>Sometimes you need to call a word before it is defined. For this, you can
-use the <code>FORWARD</code> declaration. It looks like this</p>
+use the <code>FORWARD</code> declaration. It looks like this:</p>
<p><code>FORWARD name ;</code></p>
<p>This simply states to Stacker that "name" is the name of a definition
that is defined elsewhere. Generally it means the definition can be found
<p>The built-in words of the Stacker language are put in several groups
depending on what they do. The groups are as follows:</p>
<ol>
- <li><em>Logical</em>These words provide the logical operations for
+ <li><em>Logical</em>: These words provide the logical operations for
comparing stack operands.<br/>The words are: < > <= >=
= <> true false.</li>
- <li><em>Bitwise</em>These words perform bitwise computations on
+ <li><em>Bitwise</em>: These words perform bitwise computations on
their operands. <br/> The words are: << >> XOR AND NOT</li>
- <li><em>Arithmetic</em>These words perform arithmetic computations on
+ <li><em>Arithmetic</em>: These words perform arithmetic computations on
their operands. <br/> The words are: ABS NEG + - * / MOD */ ++ -- MIN MAX</li>
<li><em>Stack</em>These words manipulate the stack directly by moving
- its elements around.<br/> The words are: DROP DUP SWAP OVER ROT DUP2 DROP2 PICK TUCK</li>
- <li><em>Memory</em>These words allocate, free and manipulate memory
+ its elements around.<br/> The words are: DROP DROP2 NIP NIP2 DUP DUP2
+ SWAP SWAP2 OVER OVER2 ROT ROT2 RROT RROT2 TUCK TUCK2 PICK SELECT ROLL</li>
+ <li><em>Memory</em>These words allocate, free, and manipulate memory
areas outside the stack.<br/>The words are: MALLOC FREE GET PUT</li>
- <li><em>Control</em>These words alter the normal left to right flow
+ <li><em>Control</em>: These words alter the normal left to right flow
of execution.<br/>The words are: IF ELSE ENDIF WHILE END RETURN EXIT RECURSE</li>
- <li><em>I/O</em> These words perform output on the standard output
+ <li><em>I/O</em>: These words perform output on the standard output
and input on the standard input. No other I/O is possible in Stacker.
<br/>The words are: SPACE TAB CR >s >d >c <s <d <c.</li>
</ol>
<li><em>b</em> - a boolean truth value</li>
<li><em>w</em> - a normal integer valued word.</li>
<li><em>s</em> - a pointer to a string value</li>
- <li><em>p</em> - a pointer to a malloc's memory block</li>
+ <li><em>p</em> - a pointer to a malloc'd memory block</li>
</ol>
</div>
-<div class="doc_text">
-<table class="doc_table" >
-<tr class="doc_table"><td colspan="4">Definition Of Operation Of Built In Words</td></tr>
-<tr class="doc_table"><td colspan="4">LOGICAL OPERATIONS</td></tr>
-<tr class="doc_table"><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
-<tr class="doc_table"><td><</td>
- <td>LT</td>
- <td>w1 w2 -- b</td>
- <td>Two values (w1 and w2) are popped off the stack and
+<div class="doc_text" >
+ <table class="doc_table" style="border: 2px solid blue; border-collapse: collapse;" >
+<tr class="doc_table"><td colspan="4" style="border: 2px solid blue">Definition Of Operation Of Built In Words</td></tr>
+<tr class="doc_table"><td colspan="4" style="border: 2px solid blue"><b>LOGICAL OPERATIONS</b></td></tr>
+<tr class="doc_table">
+ <td style="border: 2px solid blue"><u>Word</u></td>
+ <td style="border: 2px solid blue"><u>Name</u></td>
+ <td style="border: 2px solid blue"><u>Operation</u></td>
+ <td style="border: 2px solid blue"><u>Description</u></td>
+</tr>
+<tr class="doc_table"><td style="border: 2px solid blue"><</td>
+ <td style="border: 2px solid blue">LT</td>
+ <td style="border: 2px solid blue">w1 w2 -- b</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack and
compared. If w1 is less than w2, TRUE is pushed back on
the stack, otherwise FALSE is pushed back on the stack.</td>
</tr>
-<tr><td>></td>
- <td>GT</td>
- <td>w1 w2 -- b</td>
- <td>Two values (w1 and w2) are popped off the stack and
+<tr><td style="border: 2px solid blue">></td>
+ <td style="border: 2px solid blue">GT</td>
+ <td style="border: 2px solid blue">w1 w2 -- b</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack and
compared. If w1 is greater than w2, TRUE is pushed back on
the stack, otherwise FALSE is pushed back on the stack.</td>
</tr>
-<tr><td>>=</td>
- <td>GE</td>
- <td>w1 w2 -- b</td>
- <td>Two values (w1 and w2) are popped off the stack and
+<tr><td style="border: 2px solid blue">>=</td>
+ <td style="border: 2px solid blue">GE</td>
+ <td style="border: 2px solid blue">w1 w2 -- b</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack and
compared. If w1 is greater than or equal to w2, TRUE is
pushed back on the stack, otherwise FALSE is pushed back
on the stack.</td>
</tr>
-<tr><td><=</td>
- <td>LE</td>
- <td>w1 w2 -- b</td>
- <td>Two values (w1 and w2) are popped off the stack and
+<tr><td style="border: 2px solid blue"><=</td>
+ <td style="border: 2px solid blue">LE</td>
+ <td style="border: 2px solid blue">w1 w2 -- b</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack and
compared. If w1 is less than or equal to w2, TRUE is
pushed back on the stack, otherwise FALSE is pushed back
on the stack.</td>
</tr>
-<tr><td>=</td>
- <td>EQ</td>
- <td>w1 w2 -- b</td>
- <td>Two values (w1 and w2) are popped off the stack and
+<tr><td style="border: 2px solid blue">=</td>
+ <td style="border: 2px solid blue">EQ</td>
+ <td style="border: 2px solid blue">w1 w2 -- b</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack and
compared. If w1 is equal to w2, TRUE is
pushed back on the stack, otherwise FALSE is pushed back
</td>
</tr>
-<tr><td><></td>
- <td>NE</td>
- <td>w1 w2 -- b</td>
- <td>Two values (w1 and w2) are popped off the stack and
+<tr><td style="border: 2px solid blue"><></td>
+ <td style="border: 2px solid blue">NE</td>
+ <td style="border: 2px solid blue">w1 w2 -- b</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack and
compared. If w1 is equal to w2, TRUE is
pushed back on the stack, otherwise FALSE is pushed back
</td>
</tr>
-<tr><td>FALSE</td>
- <td>FALSE</td>
- <td> -- b</td>
- <td>The boolean value FALSE (0) is pushed onto the stack.</td>
-</tr>
-<tr><td>TRUE</td>
- <td>TRUE</td>
- <td> -- b</td>
- <td>The boolean value TRUE (-1) is pushed onto the stack.</td>
-</tr>
-<tr><td colspan="4">BITWISE OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
-<tr><td><<</td>
- <td>SHL</td>
- <td>w1 w2 -- w1<<w2</td>
- <td>Two values (w1 and w2) are popped off the stack. The w2
+<tr><td style="border: 2px solid blue">FALSE</td>
+ <td style="border: 2px solid blue">FALSE</td>
+ <td style="border: 2px solid blue"> -- b</td>
+ <td style="border: 2px solid blue">The boolean value FALSE (0) is pushed on to the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue">TRUE</td>
+ <td style="border: 2px solid blue">TRUE</td>
+ <td style="border: 2px solid blue"> -- b</td>
+ <td style="border: 2px solid blue">The boolean value TRUE (-1) is pushed on to the stack.</td>
+</tr>
+<tr><td colspan="4"><b>BITWISE OPERATORS</b></td></tr>
+<tr>
+ <td style="border: 2px solid blue"><u>Word</u></td>
+ <td style="border: 2px solid blue"><u>Name</u></td>
+ <td style="border: 2px solid blue"><u>Operation</u></td>
+ <td style="border: 2px solid blue"><u>Description</u></td>
+</tr>
+<tr><td style="border: 2px solid blue"><<</td>
+ <td style="border: 2px solid blue">SHL</td>
+ <td style="border: 2px solid blue">w1 w2 -- w1<<w2</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack. The w2
operand is shifted left by the number of bits given by the
w1 operand. The result is pushed back to the stack.</td>
</tr>
-<tr><td>>></td>
- <td>SHR</td>
- <td>w1 w2 -- w1>>w2</td>
- <td>Two values (w1 and w2) are popped off the stack. The w2
+<tr><td style="border: 2px solid blue">>></td>
+ <td style="border: 2px solid blue">SHR</td>
+ <td style="border: 2px solid blue">w1 w2 -- w1>>w2</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack. The w2
operand is shifted right by the number of bits given by the
w1 operand. The result is pushed back to the stack.</td>
</tr>
-<tr><td>OR</td>
- <td>OR</td>
- <td>w1 w2 -- w2|w1</td>
- <td>Two values (w1 and w2) are popped off the stack. The values
+<tr><td style="border: 2px solid blue">OR</td>
+ <td style="border: 2px solid blue">OR</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2|w1</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack. The values
are bitwise OR'd together and pushed back on the stack. This is
not a logical OR. The sequence 1 2 OR yields 3 not 1.</td>
</tr>
-<tr><td>AND</td>
- <td>AND</td>
- <td>w1 w2 -- w2&w1</td>
- <td>Two values (w1 and w2) are popped off the stack. The values
+<tr><td style="border: 2px solid blue">AND</td>
+ <td style="border: 2px solid blue">AND</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2&w1</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack. The values
are bitwise AND'd together and pushed back on the stack. This is
not a logical AND. The sequence 1 2 AND yields 0 not 1.</td>
</tr>
-<tr><td>XOR</td>
- <td>XOR</td>
- <td>w1 w2 -- w2^w1</td>
- <td>Two values (w1 and w2) are popped off the stack. The values
+<tr><td style="border: 2px solid blue">XOR</td>
+ <td style="border: 2px solid blue">XOR</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2^w1</td>
+ <td style="border: 2px solid blue">Two values (w1 and w2) are popped off the stack. The values
are bitwise exclusive OR'd together and pushed back on the stack.
For example, The sequence 1 3 XOR yields 2.</td>
</tr>
-<tr><td colspan="4">ARITHMETIC OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
-<tr><td>ABS</td>
- <td>ABS</td>
- <td>w -- |w|</td>
- <td>One value s popped off the stack; its absolute value is computed
- and then pushed onto the stack. If w1 is -1 then w2 is 1. If w1 is
+<tr><td colspan="4"><b>ARITHMETIC OPERATORS</b></td></tr>
+<tr>
+ <td style="border: 2px solid blue"><u>Word</u></td>
+ <td style="border: 2px solid blue"><u>Name</u></td>
+ <td style="border: 2px solid blue"><u>Operation</u></td>
+ <td style="border: 2px solid blue"><u>Description</u></td>
+</tr>
+<tr><td style="border: 2px solid blue">ABS</td>
+ <td style="border: 2px solid blue">ABS</td>
+ <td style="border: 2px solid blue">w -- |w|</td>
+ <td style="border: 2px solid blue">One value s popped off the stack; its absolute value is computed
+ and then pushed on to the stack. If w1 is -1 then w2 is 1. If w1 is
1 then w2 is also 1.</td>
</tr>
-<tr><td>NEG</td>
- <td>NEG</td>
- <td>w -- -w</td>
- <td>One value is popped off the stack which is negated and then
- pushed back onto the stack. If w1 is -1 then w2 is 1. If w1 is
+<tr><td style="border: 2px solid blue">NEG</td>
+ <td style="border: 2px solid blue">NEG</td>
+ <td style="border: 2px solid blue">w -- -w</td>
+ <td style="border: 2px solid blue">One value is popped off the stack which is negated and then
+ pushed back on to the stack. If w1 is -1 then w2 is 1. If w1 is
1 then w2 is -1.</td>
</tr>
-<tr><td> + </td>
- <td>ADD</td>
- <td>w1 w2 -- w2+w1</td>
- <td>Two values are popped off the stack. Their sum is pushed back
- onto the stack</td>
-</tr>
-<tr><td> - </td>
- <td>SUB</td>
- <td>w1 w2 -- w2-w1</td>
- <td>Two values are popped off the stack. Their difference is pushed back
- onto the stack</td>
-</tr>
-<tr><td> * </td>
- <td>MUL</td>
- <td>w1 w2 -- w2*w1</td>
- <td>Two values are popped off the stack. Their product is pushed back
- onto the stack</td>
-</tr>
-<tr><td> / </td>
- <td>DIV</td>
- <td>w1 w2 -- w2/w1</td>
- <td>Two values are popped off the stack. Their quotient is pushed back
- onto the stack</td>
-</tr>
-<tr><td>MOD</td>
- <td>MOD</td>
- <td>w1 w2 -- w2%w1</td>
- <td>Two values are popped off the stack. Their remainder after division
- of w1 by w2 is pushed back onto the stack</td>
-</tr>
-<tr><td> */ </td>
- <td>STAR_SLAH</td>
- <td>w1 w2 w3 -- (w3*w2)/w1</td>
- <td>Three values are popped off the stack. The product of w1 and w2 is
- divided by w3. The result is pushed back onto the stack.</td>
-</tr>
-<tr><td> ++ </td>
- <td>INCR</td>
- <td>w -- w+1</td>
- <td>One value is popped off the stack. It is incremented by one and then
- pushed back onto the stack.</td>
-</tr>
-<tr><td> -- </td>
- <td>DECR</td>
- <td>w -- w-1</td>
- <td>One value is popped off the stack. It is decremented by one and then
- pushed back onto the stack.</td>
-</tr>
-<tr><td>MIN</td>
- <td>MIN</td>
- <td>w1 w2 -- (w2<w1?w2:w1)</td>
- <td>Two values are popped off the stack. The larger one is pushed back
- onto the stack.</td>
-</tr>
-<tr><td>MAX</td>
- <td>MAX</td>
- <td>w1 w2 -- (w2>w1?w2:w1)</td>
- <td>Two values are popped off the stack. The larger value is pushed back
- onto the stack.</td>
-</tr>
-<tr><td colspan="4">STACK MANIPULATION OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
-<tr><td>DROP</td>
- <td>DROP</td>
- <td>w -- </td>
- <td>One value is popped off the stack.</td>
-</tr>
-<tr><td>DROP2</td>
- <td>DROP2</td>
- <td>w1 w2 -- </td>
- <td>Two values are popped off the stack.</td>
-</tr>
-<tr><td>NIP</td>
- <td>NIP</td>
- <td>w1 w2 -- w2</td>
- <td>The second value on the stack is removed from the stack. That is,
+<tr><td style="border: 2px solid blue"> + </td>
+ <td style="border: 2px solid blue">ADD</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2+w1</td>
+ <td style="border: 2px solid blue">Two values are popped off the stack. Their sum is pushed back
+ on to the stack</td>
+</tr>
+<tr><td style="border: 2px solid blue"> - </td>
+ <td style="border: 2px solid blue">SUB</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2-w1</td>
+ <td style="border: 2px solid blue">Two values are popped off the stack. Their difference is pushed back
+ on to the stack</td>
+</tr>
+<tr><td style="border: 2px solid blue"> * </td>
+ <td style="border: 2px solid blue">MUL</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2*w1</td>
+ <td style="border: 2px solid blue">Two values are popped off the stack. Their product is pushed back
+ on to the stack</td>
+</tr>
+<tr><td style="border: 2px solid blue"> / </td>
+ <td style="border: 2px solid blue">DIV</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2/w1</td>
+ <td style="border: 2px solid blue">Two values are popped off the stack. Their quotient is pushed back
+ on to the stack</td>
+</tr>
+<tr><td style="border: 2px solid blue">MOD</td>
+ <td style="border: 2px solid blue">MOD</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2%w1</td>
+ <td style="border: 2px solid blue">Two values are popped off the stack. Their remainder after division
+ of w1 by w2 is pushed back on to the stack</td>
+</tr>
+<tr><td style="border: 2px solid blue"> */ </td>
+ <td style="border: 2px solid blue">STAR_SLAH</td>
+ <td style="border: 2px solid blue">w1 w2 w3 -- (w3*w2)/w1</td>
+ <td style="border: 2px solid blue">Three values are popped off the stack. The product of w1 and w2 is
+ divided by w3. The result is pushed back on to the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue"> ++ </td>
+ <td style="border: 2px solid blue">INCR</td>
+ <td style="border: 2px solid blue">w -- w+1</td>
+ <td style="border: 2px solid blue">One value is popped off the stack. It is incremented by one and then
+ pushed back on to the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">DECR</td>
+ <td style="border: 2px solid blue">w -- w-1</td>
+ <td style="border: 2px solid blue">One value is popped off the stack. It is decremented by one and then
+ pushed back on to the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue">MIN</td>
+ <td style="border: 2px solid blue">MIN</td>
+ <td style="border: 2px solid blue">w1 w2 -- (w2<w1?w2:w1)</td>
+ <td style="border: 2px solid blue">Two values are popped off the stack. The larger one is pushed back
+ on to the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue">MAX</td>
+ <td style="border: 2px solid blue">MAX</td>
+ <td style="border: 2px solid blue">w1 w2 -- (w2>w1?w2:w1)</td>
+ <td style="border: 2px solid blue">Two values are popped off the stack. The larger value is pushed back
+ on to the stack.</td>
+</tr>
+<tr><td colspan="4"><b>STACK MANIPULATION OPERATORS</b></td></tr>
+<tr>
+ <td style="border: 2px solid blue"><u>Word</u></td>
+ <td style="border: 2px solid blue"><u>Name</u></td>
+ <td style="border: 2px solid blue"><u>Operation</u></td>
+ <td style="border: 2px solid blue"><u>Description</u></td>
+</tr>
+<tr><td style="border: 2px solid blue">DROP</td>
+ <td style="border: 2px solid blue">DROP</td>
+ <td style="border: 2px solid blue">w -- </td>
+ <td style="border: 2px solid blue">One value is popped off the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue">DROP2</td>
+ <td style="border: 2px solid blue">DROP2</td>
+ <td style="border: 2px solid blue">w1 w2 -- </td>
+ <td style="border: 2px solid blue">Two values are popped off the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue">NIP</td>
+ <td style="border: 2px solid blue">NIP</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2</td>
+ <td style="border: 2px solid blue">The second value on the stack is removed from the stack. That is,
a value is popped off the stack and retained. Then a second value is
popped and the retained value is pushed.</td>
</tr>
-<tr><td>NIP2</td>
- <td>NIP2</td>
- <td>w1 w2 w3 w4 -- w3 w4</td>
- <td>The third and fourth values on the stack are removed from it. That is,
+<tr><td style="border: 2px solid blue">NIP2</td>
+ <td style="border: 2px solid blue">NIP2</td>
+ <td style="border: 2px solid blue">w1 w2 w3 w4 -- w3 w4</td>
+ <td style="border: 2px solid blue">The third and fourth values on the stack are removed from it. That is,
two values are popped and retained. Then two more values are popped and
the two retained values are pushed back on.</td>
</tr>
-<tr><td>DUP</td>
- <td>DUP</td>
- <td>w1 -- w1 w1</td>
- <td>One value is popped off the stack. That value is then pushed onto
+<tr><td style="border: 2px solid blue">DUP</td>
+ <td style="border: 2px solid blue">DUP</td>
+ <td style="border: 2px solid blue">w1 -- w1 w1</td>
+ <td style="border: 2px solid blue">One value is popped off the stack. That value is then pushed on to
the stack twice to duplicate the top stack vaue.</td>
</tr>
-<tr><td>DUP2</td>
- <td>DUP2</td>
- <td>w1 w2 -- w1 w2 w1 w2</td>
- <td>The top two values on the stack are duplicated. That is, two vaues
+<tr><td style="border: 2px solid blue">DUP2</td>
+ <td style="border: 2px solid blue">DUP2</td>
+ <td style="border: 2px solid blue">w1 w2 -- w1 w2 w1 w2</td>
+ <td style="border: 2px solid blue">The top two values on the stack are duplicated. That is, two vaues
are popped off the stack. They are alternately pushed back on the
stack twice each.</td>
</tr>
-<tr><td>SWAP</td>
- <td>SWAP</td>
- <td>w1 w2 -- w2 w1</td>
- <td>The top two stack items are reversed in their order. That is, two
- values are popped off the stack and pushed back onto the stack in
+<tr><td style="border: 2px solid blue">SWAP</td>
+ <td style="border: 2px solid blue">SWAP</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2 w1</td>
+ <td style="border: 2px solid blue">The top two stack items are reversed in their order. That is, two
+ values are popped off the stack and pushed back on to the stack in
the opposite order they were popped.</td>
</tr>
-<tr><td>SWAP2</td>
- <td>SWAP2</td>
- <td>w1 w2 w3 w4 -- w3 w4 w2 w1</td>
- <td>The top four stack items are swapped in pairs. That is, two values
+<tr><td style="border: 2px solid blue">SWAP2</td>
+ <td style="border: 2px solid blue">SWAP2</td>
+ <td style="border: 2px solid blue">w1 w2 w3 w4 -- w3 w4 w2 w1</td>
+ <td style="border: 2px solid blue">The top four stack items are swapped in pairs. That is, two values
are popped and retained. Then, two more values are popped and retained.
- The values are pushed back onto the stack in the reverse order but
+ The values are pushed back on to the stack in the reverse order but
in pairs.</p>
</tr>
-<tr><td>OVER</td>
- <td>OVER</td>
- <td>w1 w2-- w1 w2 w1</td>
- <td>Two values are popped from the stack. They are pushed back
- onto the stack in the order w1 w2 w1. This seems to cause the
+<tr><td style="border: 2px solid blue">OVER</td>
+ <td style="border: 2px solid blue">OVER</td>
+ <td style="border: 2px solid blue">w1 w2-- w1 w2 w1</td>
+ <td style="border: 2px solid blue">Two values are popped from the stack. They are pushed back
+ on to the stack in the order w1 w2 w1. This seems to cause the
top stack element to be duplicated "over" the next value.</td>
</tr>
-<tr><td>OVER2</td>
- <td>OVER2</td>
- <td>w1 w2 w3 w4 -- w1 w2 w3 w4 w1 w2</td>
- <td>The third and fourth values on the stack are replicated onto the
+<tr><td style="border: 2px solid blue">OVER2</td>
+ <td style="border: 2px solid blue">OVER2</td>
+ <td style="border: 2px solid blue">w1 w2 w3 w4 -- w1 w2 w3 w4 w1 w2</td>
+ <td style="border: 2px solid blue">The third and fourth values on the stack are replicated on to the
top of the stack</td>
</tr>
-<tr><td>ROT</td>
- <td>ROT</td>
- <td>w1 w2 w3 -- w2 w3 w1</td>
- <td>The top three values are rotated. That is, three value are popped
- off the stack. They are pushed back onto the stack in the order
+<tr><td style="border: 2px solid blue">ROT</td>
+ <td style="border: 2px solid blue">ROT</td>
+ <td style="border: 2px solid blue">w1 w2 w3 -- w2 w3 w1</td>
+ <td style="border: 2px solid blue">The top three values are rotated. That is, three value are popped
+ off the stack. They are pushed back on to the stack in the order
w1 w3 w2.</td>
</tr>
-<tr><td>ROT2</td>
- <td>ROT2</td>
- <td>w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td>
- <td>Like ROT but the rotation is done using three pairs instead of
+<tr><td style="border: 2px solid blue">ROT2</td>
+ <td style="border: 2px solid blue">ROT2</td>
+ <td style="border: 2px solid blue">w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td>
+ <td style="border: 2px solid blue">Like ROT but the rotation is done using three pairs instead of
three singles.</td>
</tr>
-<tr><td>RROT</td>
- <td>RROT</td>
- <td>w1 w2 w3 -- w2 w3 w1</td>
- <td>Reverse rotation. Like ROT, but it rotates the other way around.
+<tr><td style="border: 2px solid blue">RROT</td>
+ <td style="border: 2px solid blue">RROT</td>
+ <td style="border: 2px solid blue">w1 w2 w3 -- w2 w3 w1</td>
+ <td style="border: 2px solid blue">Reverse rotation. Like ROT, but it rotates the other way around.
Essentially, the third element on the stack is moved to the top
of the stack.</td>
</tr>
-<tr><td>RROT2</td>
- <td>RROT2</td>
- <td>w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td>
- <td>Double reverse rotation. Like RROT but the rotation is done using
+<tr><td style="border: 2px solid blue">RROT2</td>
+ <td style="border: 2px solid blue">RROT2</td>
+ <td style="border: 2px solid blue">w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td>
+ <td style="border: 2px solid blue">Double reverse rotation. Like RROT but the rotation is done using
three pairs instead of three singles. The fifth and sixth stack
elements are moved to the first and second positions</td>
</tr>
-<tr><td>TUCK</td>
- <td>TUCK</td>
- <td>w1 w2 -- w2 w1 w2</td>
- <td>Similar to OVER except that the second operand is being
+<tr><td style="border: 2px solid blue">TUCK</td>
+ <td style="border: 2px solid blue">TUCK</td>
+ <td style="border: 2px solid blue">w1 w2 -- w2 w1 w2</td>
+ <td style="border: 2px solid blue">Similar to OVER except that the second operand is being
replicated. Essentially, the first operand is being "tucked"
in between two instances of the second operand. Logically, two
values are popped off the stack. They are placed back on the
stack in the order w2 w1 w2.</td>
</tr>
-<tr><td>TUCK2</td>
- <td>TUCK2</td>
- <td>w1 w2 w3 w4 -- w3 w4 w1 w2 w3 w4</td>
- <td>Like TUCK but a pair of elements is tucked over two pairs.
+<tr><td style="border: 2px solid blue">TUCK2</td>
+ <td style="border: 2px solid blue">TUCK2</td>
+ <td style="border: 2px solid blue">w1 w2 w3 w4 -- w3 w4 w1 w2 w3 w4</td>
+ <td style="border: 2px solid blue">Like TUCK but a pair of elements is tucked over two pairs.
That is, the top two elements of the stack are duplicated and
inserted into the stack at the fifth and positions.</td>
</tr>
-<tr><td>PICK</td>
- <td>PICK</td>
- <td>x0 ... Xn n -- x0 ... Xn x0</td>
- <td>The top of the stack is used as an index into the remainder of
+<tr><td style="border: 2px solid blue">PICK</td>
+ <td style="border: 2px solid blue">PICK</td>
+ <td style="border: 2px solid blue">x0 ... Xn n -- x0 ... Xn x0</td>
+ <td style="border: 2px solid blue">The top of the stack is used as an index into the remainder of
the stack. The element at the nth position replaces the index
(top of stack). This is useful for cycling through a set of
values. Note that indexing is zero based. So, if n=0 then you
get the second item on the stack. If n=1 you get the third, etc.
Note also that the index is replaced by the n'th value. </td>
</tr>
-<tr><td>SELECT</td>
- <td>SELECT</td>
- <td>m n X0..Xm Xm+1 .. Xn -- Xm</td>
- <td>This is like PICK but the list is removed and you need to specify
+<tr><td style="border: 2px solid blue">SELECT</td>
+ <td style="border: 2px solid blue">SELECT</td>
+ <td style="border: 2px solid blue">m n X0..Xm Xm+1 .. Xn -- Xm</td>
+ <td style="border: 2px solid blue">This is like PICK but the list is removed and you need to specify
both the index and the size of the list. Careful with this one,
the wrong value for n can blow away a huge amount of the stack.</td>
</tr>
-<tr><td>ROLL</td>
- <td>ROLL</td>
- <td>x0 x1 .. xn n -- x1 .. xn x0</td>
- <td><b>Not Implemented</b>. This one has been left as an exercise to
- the student. If you can implement this one you understand Stacker
- and probably a fair amount about LLVM since this is one of the
- more complicated Stacker operations. See the StackerCompiler.cpp
- file in the projects/Stacker/lib/compiler directory. The operation
- of ROLL is like a generalized ROT. That is ROLL with n=1 is the
- same as ROT. The n value (top of stack) is used as an index to
- select a value up the stack that is <em>moved</em> to the top of
- the stack. See the implementations of PICk and SELECT to get
- some hints.<p>
-</tr>
-<tr><td colspan="4">MEMORY OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
-<tr><td>MALLOC</td>
- <td>MALLOC</td>
- <td>w1 -- p</td>
- <td>One value is popped off the stack. The value is used as the size
+<tr><td style="border: 2px solid blue">ROLL</td>
+ <td style="border: 2px solid blue">ROLL</td>
+ <td style="border: 2px solid blue">x0 x1 .. xn n -- x1 .. xn x0</td>
+ <td style="border: 2px solid blue"><b>Not Implemented</b>. This one has been left as an exercise to
+ the student. See <a href="#exercise">Exercise</a>. ROLL requires
+ a value, "n", to be on the top of the stack. This value specifies how
+ far into the stack to "roll". The n'th value is <em>moved</em> (not
+ copied) from its location and replaces the "n" value on the top of the
+ stack. In this way, all the values between "n" and x0 roll up the stack.
+ The operation of ROLL is a generalized ROT. The "n" value specifies
+ how much to rotate. That is, ROLL with n=1 is the same as ROT and
+ ROLL with n=2 is the same as ROT2.</td>
+</tr>
+<tr><td colspan="4"><b>MEMORY OPERATORS</b></td></tr>
+<tr>
+ <td style="border: 2px solid blue"><u>Word</u></td>
+ <td style="border: 2px solid blue"><u>Name</u></td>
+ <td style="border: 2px solid blue"><u>Operation</u></td>
+ <td style="border: 2px solid blue"><u>Description</u></td>
+</tr>
+<tr><td style="border: 2px solid blue">MALLOC</td>
+ <td style="border: 2px solid blue">MALLOC</td>
+ <td style="border: 2px solid blue">w1 -- p</td>
+ <td style="border: 2px solid blue">One value is popped off the stack. The value is used as the size
of a memory block to allocate. The size is in bytes, not words.
The memory allocation is completed and the address of the memory
- block is pushed onto the stack.</td>
+ block is pushed on to the stack.</td>
</tr>
-<tr><td>FREE</td>
- <td>FREE</td>
- <td>p -- </td>
- <td>One pointer value is popped off the stack. The value should be
+<tr><td style="border: 2px solid blue">FREE</td>
+ <td style="border: 2px solid blue">FREE</td>
+ <td style="border: 2px solid blue">p -- </td>
+ <td style="border: 2px solid blue">One pointer value is popped off the stack. The value should be
the address of a memory block created by the MALLOC operation. The
associated memory block is freed. Nothing is pushed back on the
stack. Many bugs can be created by attempting to FREE something
the stack (for the FREE at the end) and that every use of the
pointer is preceded by a DUP to retain the copy for FREE.</td>
</tr>
-<tr><td>GET</td>
- <td>GET</td>
- <td>w1 p -- w2 p</td>
- <td>An integer index and a pointer to a memory block are popped of
+<tr><td style="border: 2px solid blue">GET</td>
+ <td style="border: 2px solid blue">GET</td>
+ <td style="border: 2px solid blue">w1 p -- w2 p</td>
+ <td style="border: 2px solid blue">An integer index and a pointer to a memory block are popped of
the block. The index is used to index one byte from the memory
block. That byte value is retained, the pointer is pushed again
and the retained value is pushed. Note that the pointer value
s essentially retained in its position so this doesn't count
as a "use ptr" in the FREE idiom.</td>
</tr>
-<tr><td>PUT</td>
- <td>PUT</td>
- <td>w1 w2 p -- p </td>
- <td>An integer value is popped of the stack. This is the value to
+<tr><td style="border: 2px solid blue">PUT</td>
+ <td style="border: 2px solid blue">PUT</td>
+ <td style="border: 2px solid blue">w1 w2 p -- p </td>
+ <td style="border: 2px solid blue">An integer value is popped of the stack. This is the value to
be put into a memory block. Another integer value is popped of
the stack. This is the indexed byte in the memory block. A
pointer to the memory block is popped off the stack. The
pushed back on the stack so this doesn't count as a "use ptr"
in the FREE idiom.</td>
</tr>
-<tr><td colspan="4">CONTROL FLOW OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
-<tr><td>RETURN</td>
- <td>RETURN</td>
- <td> -- </td>
- <td>The currently executing definition returns immediately to its caller.
+<tr><td colspan="4"><b>CONTROL FLOW OPERATORS</b></td></tr>
+<tr>
+ <td style="border: 2px solid blue"><u>Word</u></td>
+ <td style="border: 2px solid blue"><u>Name</u></td>
+ <td style="border: 2px solid blue"><u>Operation</u></td>
+ <td style="border: 2px solid blue"><u>Description</u></td>
+</tr>
+<tr><td style="border: 2px solid blue">RETURN</td>
+ <td style="border: 2px solid blue">RETURN</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">The currently executing definition returns immediately to its caller.
Note that there is an implicit <code>RETURN</code> at the end of each
definition, logically located at the semi-colon. The sequence
<code>RETURN ;</code> is valid but redundant.</td>
</tr>
-<tr><td>EXIT</td>
- <td>EXIT</td>
- <td>w1 -- </td>
- <td>A return value for the program is popped off the stack. The program is
+<tr><td style="border: 2px solid blue">EXIT</td>
+ <td style="border: 2px solid blue">EXIT</td>
+ <td style="border: 2px solid blue">w1 -- </td>
+ <td style="border: 2px solid blue">A return value for the program is popped off the stack. The program is
then immediately terminated. This is normally an abnormal exit from the
program. For a normal exit (when <code>MAIN</code> finishes), the exit
code will always be zero in accordance with UNIX conventions.</td>
</tr>
-<tr><td>RECURSE</td>
- <td>RECURSE</td>
- <td> -- </td>
- <td>The currently executed definition is called again. This operation is
+<tr><td style="border: 2px solid blue">RECURSE</td>
+ <td style="border: 2px solid blue">RECURSE</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">The currently executed definition is called again. This operation is
needed since the definition of a word doesn't exist until the semi colon
is reacher. Attempting something like:<br/>
<code> : recurser recurser ; </code><br/> will yield and error saying that
to:<br/>
<code> : recurser RECURSE ; </code></td>
</tr>
-<tr><td>IF (words...) ENDIF</td>
- <td>IF (words...) ENDIF</td>
- <td>b -- </td>
- <td>A boolean value is popped of the stack. If it is non-zero then the "words..."
+<tr><td style="border: 2px solid blue">IF (words...) ENDIF</td>
+ <td style="border: 2px solid blue">IF (words...) ENDIF</td>
+ <td style="border: 2px solid blue">b -- </td>
+ <td style="border: 2px solid blue">A boolean value is popped of the stack. If it is non-zero then the "words..."
are executed. Otherwise, execution continues immediately following the ENDIF.</td>
</tr>
-<tr><td>IF (words...) ELSE (words...) ENDIF</td>
- <td>IF (words...) ELSE (words...) ENDIF</td>
- <td>b -- </td>
- <td>A boolean value is popped of the stack. If it is non-zero then the "words..."
+<tr><td style="border: 2px solid blue">IF (words...) ELSE (words...) ENDIF</td>
+ <td style="border: 2px solid blue">IF (words...) ELSE (words...) ENDIF</td>
+ <td style="border: 2px solid blue">b -- </td>
+ <td style="border: 2px solid blue">A boolean value is popped of the stack. If it is non-zero then the "words..."
between IF and ELSE are executed. Otherwise the words between ELSE and ENDIF are
executed. In either case, after the (words....) have executed, execution continues
immediately following the ENDIF. </td>
</tr>
-<tr><td>WHILE (words...) END</td>
- <td>WHILE (words...) END</td>
- <td>b -- b </td>
- <td>The boolean value on the top of the stack is examined. If it is non-zero then the
+<tr><td style="border: 2px solid blue">WHILE (words...) END</td>
+ <td style="border: 2px solid blue">WHILE (words...) END</td>
+ <td style="border: 2px solid blue">b -- b </td>
+ <td style="border: 2px solid blue">The boolean value on the top of the stack is examined. If it is non-zero then the
"words..." between WHILE and END are executed. Execution then begins again at the WHILE where another
boolean is popped off the stack. To prevent this operation from eating up the entire
- stack, you should push onto the stack (just before the END) a boolean value that indicates
+ stack, you should push on to the stack (just before the END) a boolean value that indicates
whether to terminate. Note that since booleans and integers can be coerced you can
use the following "for loop" idiom:<br/>
<code>(push count) WHILE (words...) -- END</code><br/>
the top of stack is decremented to 0 at which the WHILE test fails and control is
transfered to the word after the END.</td>
</tr>
-<tr><td colspan="4">INPUT & OUTPUT OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
-<tr><td>SPACE</td>
- <td>SPACE</td>
- <td> -- </td>
- <td>A space character is put out. There is no stack effect.</td>
-</tr>
-<tr><td>TAB</td>
- <td>TAB</td>
- <td> -- </td>
- <td>A tab character is put out. There is no stack effect.</td>
-</tr>
-<tr><td>CR</td>
- <td>CR</td>
- <td> -- </td>
- <td>A carriage return character is put out. There is no stack effect.</td>
-</tr>
-<tr><td>>s</td>
- <td>OUT_STR</td>
- <td> -- </td>
- <td>A string pointer is popped from the stack. It is put out.</td>
-</tr>
-<tr><td>>d</td>
- <td>OUT_STR</td>
- <td> -- </td>
- <td>A value is popped from the stack. It is put out as a decimal integer.</td>
-</tr>
-<tr><td>>c</td>
- <td>OUT_CHR</td>
- <td> -- </td>
- <td>A value is popped from the stack. It is put out as an ASCII character.</td>
-</tr>
-<tr><td><s</td>
- <td>IN_STR</td>
- <td> -- s </td>
- <td>A string is read from the input via the scanf(3) format string " %as". The
- resulting string is pushed onto the stack.</td>
-</tr>
-<tr><td><d</td>
- <td>IN_STR</td>
- <td> -- w </td>
- <td>An integer is read from the input via the scanf(3) format string " %d". The
- resulting value is pushed onto the stack</td>
-</tr>
-<tr><td><c</td>
- <td>IN_CHR</td>
- <td> -- w </td>
- <td>A single character is read from the input via the scanf(3) format string
- " %c". The value is converted to an integer and pushed onto the stack.</td>
-</tr>
-<tr><td>DUMP</td>
- <td>DUMP</td>
- <td> -- </td>
- <td>The stack contents are dumped to standard output. This is useful for
+<tr><td colspan="4"><b>INPUT & OUTPUT OPERATORS</b></td></tr>
+<tr>
+ <td style="border: 2px solid blue"><u>Word</u></td>
+ <td style="border: 2px solid blue"><u>Name</u></td>
+ <td style="border: 2px solid blue"><u>Operation</u></td>
+ <td style="border: 2px solid blue"><u>Description</u></td>
+</tr>
+<tr><td style="border: 2px solid blue">SPACE</td>
+ <td style="border: 2px solid blue">SPACE</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">A space character is put out. There is no stack effect.</td>
+</tr>
+<tr><td style="border: 2px solid blue">TAB</td>
+ <td style="border: 2px solid blue">TAB</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">A tab character is put out. There is no stack effect.</td>
+</tr>
+<tr><td style="border: 2px solid blue">CR</td>
+ <td style="border: 2px solid blue">CR</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">A carriage return character is put out. There is no stack effect.</td>
+</tr>
+<tr><td style="border: 2px solid blue">>s</td>
+ <td style="border: 2px solid blue">OUT_STR</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">A string pointer is popped from the stack. It is put out.</td>
+</tr>
+<tr><td style="border: 2px solid blue">>d</td>
+ <td style="border: 2px solid blue">OUT_STR</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">A value is popped from the stack. It is put out as a decimal integer.</td>
+</tr>
+<tr><td style="border: 2px solid blue">>c</td>
+ <td style="border: 2px solid blue">OUT_CHR</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">A value is popped from the stack. It is put out as an ASCII character.</td>
+</tr>
+<tr><td style="border: 2px solid blue"><s</td>
+ <td style="border: 2px solid blue">IN_STR</td>
+ <td style="border: 2px solid blue"> -- s </td>
+ <td style="border: 2px solid blue">A string is read from the input via the scanf(3) format string " %as". The
+ resulting string is pushed on to the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue"><d</td>
+ <td style="border: 2px solid blue">IN_STR</td>
+ <td style="border: 2px solid blue"> -- w </td>
+ <td style="border: 2px solid blue">An integer is read from the input via the scanf(3) format string " %d". The
+ resulting value is pushed on to the stack</td>
+</tr>
+<tr><td style="border: 2px solid blue"><c</td>
+ <td style="border: 2px solid blue">IN_CHR</td>
+ <td style="border: 2px solid blue"> -- w </td>
+ <td style="border: 2px solid blue">A single character is read from the input via the scanf(3) format string
+ " %c". The value is converted to an integer and pushed on to the stack.</td>
+</tr>
+<tr><td style="border: 2px solid blue">DUMP</td>
+ <td style="border: 2px solid blue">DUMP</td>
+ <td style="border: 2px solid blue"> -- </td>
+ <td style="border: 2px solid blue">The stack contents are dumped to standard output. This is useful for
debugging your definitions. Put DUMP at the beginning and end of a definition
to see instantly the net effect of the definition.</td>
</tr>
<div class="doc_text">
<p>The following fully documented program highlights many features of both
the Stacker language and what is possible with LLVM. The program has two modes
-of operations. If you provide numeric arguments to the program, it checks to see
-if those arguments are prime numbers, prints out the results. Without any
-aruments, the program prints out any prime numbers it finds between 1 and one
-million (there's a log of them!). The source code comments below tell the
+of operation. If you provide numeric arguments to the program, it checks to see
+if those arguments are prime numbers and prints out the results. Without any
+arguments, the program prints out any prime numbers it finds between 1 and one
+million (there's a lot of them!). The source code comments below tell the
remainder of the story.
</p>
</div>
: exit_loop FALSE;
################################################################################
-# This definition tryies an actual division of a candidate prime number. It
+# This definition tries an actual division of a candidate prime number. It
# determines whether the division loop on this candidate should continue or
# not.
# STACK<:
# STACK<:
# p - the prime number to check
# STACK>:
-# yn - boolean indiating if its a prime or not
+# yn - boolean indicating if its a prime or not
# p - the prime number checked
################################################################################
: try_harder
under the LLVM "projects" directory. You will need to obtain the LLVM sources
to find it (either via anonymous CVS or a tarball. See the
<a href="GettingStarted.html">Getting Started</a> document).</p>
-<p>Under the "projects" directory there is a directory named "stacker". That
+<p>Under the "projects" directory there is a directory named "Stacker". That
directory contains everything, as follows:</p>
<ul>
<li><em>lib</em> - contains most of the source code
<p>See projects/Stacker/test/*.st</p>
</p></div>
<!-- ======================================================================= -->
+<div class="doc_subsection"> <a name="exercise">Exercise</a></div>
+<div class="doc_text">
+<p>As you may have noted from a careful inspection of the Built-In word
+definitions, the ROLL word is not implemented. This word was left out of
+Stacker on purpose so that it can be an exercise for the student. The exercise
+is to implement the ROLL functionality (in your own workspace) and build a test
+program for it. If you can implement ROLL, you understand Stacker and probably
+a fair amount about LLVM since this is one of the more complicated Stacker
+operations. The work will almost be completely limited to the
+<a href="#compiler">compiler</a>.
+<p>The ROLL word is already recognized by both the lexer and parser but ignored
+by the compiler. That means you don't have to futz around with figuring out how
+to get the keyword recognized. It already is. The part of the compiler that
+you need to implement is the <code>ROLL</code> case in the
+<code>StackerCompiler::handle_word(int)</code> method.</p> See the implementations
+of PICk and SELECT in the same method to get some hints about how to complete
+this exercise.<p>
+<p>Good luck!</p>
+</div>
+<!-- ======================================================================= -->
+<div class="doc_subsection"> <a name="todo">Things Remaining To Be Done</a></div>
+<div class="doc_text">
+<p>The initial implementation of Stacker has several deficiencies. If you're
+interested, here are some things that could be implemented better:</p>
+<ol>
+ <li>Write an LLVM pass to compute the correct stack depth needed by the
+ program. Currently the stack is set to a fixed number which means programs
+ with large numbers of definitions might fail.</li>
+ <li>Enhance to run on 64-bit platforms like SPARC. Right now the size of a
+ pointer on 64-bit machines will cause incorrect results because of the 32-bit
+ size of a stack element currently supported. This feature was not implemented
+ because LLVM needs a union type to be able to support the different sizes
+ correctly (portably and efficiently).</li>
+ <li>Write an LLVM pass to optimize the use of the global stack. The code
+ emitted currently is somewhat wasteful. It gets cleaned up a lot by existing
+ passes but more could be done.</li>
+ <li>Add -O -O1 -O2 and -O3 optimization switches to the compiler driver to
+ allow LLVM optimization without using "opt."</li>
+ <li>Make the compiler driver use the LLVM linking facilities (with IPO) before
+ depending on GCC to do the final link.</li>
+ <li>Clean up parsing. It doesn't handle errors very well.</li>
+ <li>Rearrange the StackerCompiler.cpp code to make better use of inserting
+ instructions before a block's terminating instruction. I didn't figure this
+ technique out until I was nearly done with LLVM. As it is, its a bad example
+ of how to insert instructions!</li>
+ <li>Provide for I/O to arbitrary files instead of just stdin/stdout.</li>
+ <li>Write additional built-in words; with inspiration from FORTH</li>
+ <li>Write additional sample Stacker programs.</li>
+ <li>Add your own compiler writing experiences and tips in the
+ <a href="#lessons">Lessons I Learned About LLVM</a> section.</li>
+</ol>
+</div>
+<!-- ======================================================================= -->
<hr>
<div class="doc_footer">
<address><a href="mailto:rspencer@x10sys.com">Reid Spencer</a></address>
projects / oota-llvm.git / blobdiff