ueforth/site/common.html

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<h5>Null Terminated Strings</h5>
<p>
As null terminated strings are used throughout C interfaces,
their use is supported in Forth by way of several non-standard
words with the convention of using Z/z to refer to such strings
in names and stack comments.
</p>
<pre>
Z" ( "string" -- z ) Creates a null terminated string on the heap
Z&gt;S ( z -- a n ) Convert a null terminated string to a counted string
S&gt;Z ( a n -- z ) Conver a counted string string to null terminated (copies string to heap)
</pre>

<h5>Raw Strings</h5>
<p>
Raw strings are provided better support using a string
for the duration of the current command, without consuming heap memory.
</p>
<pre>
R" ( "string" -- a n ) Creates a temporary counted string
R| ( string| -- a n ) Creates a temporary counted string ending with |
</pre>

<h5>Utilities</h5>
<pre>
DUMP ( a n -- ) Dump a memory region
SEE ( "name" -- ) Attempt to decompile a word
VARIABLE ECHO -- Determines if commands are echoed
REMAINING ( -- n ) Bytes remaining in Forth heap.
DUMP-FILE ( data data# fn fn# -- ) Write contents of a file throws on error.
</pre>

<h5>Vocabularies</h5>
<p>
{{FORTH}} uses a hybrid of Forth-79 and Forth-83 style vocabularies.
By default vocabularies chain to the vocabulary in which they were defined,
as in Forth-79. However, like Forth-83, <code>ALSO</code>
can be used to add vocabularies to a vocabulary stack of which
<code>CONTEXT @</code> is the first item.
The word <code>ONLY</code> clears the vocabulary stack, but as there is
no separate ONLY vocabulary, it also sets <code>CONTEXT</code>
to the <code>FORTH</code> vocabulary.
The word <code>SEALED</code> modifies the most recently defined vocabulary
such that it does not chain. Note, this must be done before words are added to it.
</p>
<pre>
VOCABULARY ( "name" ) Create a vocabulary with the current vocabulary as parent
FORTH ( -- ) Make the FORTH vocabulary the context vocabulary
DEFINITIONS ( -- ) Make the context vocabulary the current vocabulary
VLIST ( -- ) List the words in the context vocabulary (not chains)
WORDS ( -- ) List the words in the context vocabulary (including chains)
TRANSFER ( "name" ) Move a word from its current dictionary to the current vocabulary
                    Useful for "hiding" built-in words
TRANSFER{ ..words.. }TRANSFER ( -- ) Transfer multiple words to the current vocabulary
ALSO ( -- ) Duplicate the vocabulary at the top of the vocabulary stack
PREVIOUS ( -- ) Drop the vocabulary at the top of the vocabulary stack
ONLY ( -- ) Reset context stack to one item, the FORTH dictionary
            Non-standard, as there's no distinct ONLY vocabulary
ORDER ( -- ) Print the vocabulary search order
SEALED ( -- ) Alter the last vocabulary defined so it doesn't chain
</pre>

<h5>Interpret Time Conditions</h5>
<p>
<code>[IF]</code>, <code>[ELSE]</code>, and <code>[THEN]</code> can be used
to selectively compile. Used in tandem with <code>DEFINED?</code> they can
be used to handle the absence of modules gracefully.
Nesting is supported.
</p>
<pre>
DEFINED? ( "name" -- xt|0 ) Check if a word exists (works at compile time too).
[IF] ( f -- ) Conditionally interpret the text the follows.
[ELSE] ( -- ) Interpret time ELSE.
[THEN] ( -- ) Interpret time THEN.
</pre>

<h5>Floating-Point</h5>
<p><b>Requires v7.0.6.5+</b></p>
<p>
Single precision floating-point support is available as a work in progress.
While initially left out in the name of minimalism,
hardware support for floating-point argues some advantages to limited support.
</p>
<p>
Floating point is kept on a separate stack.
</p>
<p>
<b>NOTE: Tasks currently don't correctly support floating point.</b>
A single floating point stack is shared by all tasks.
</p>
<pre>
FLOAT OPCODES
-------------
DOFLIT ( --- ) Puts a float from the next cell onto float stack.
FP@ ( -- a )
FP! ( a -- )
SF@ ( a -- r ) Single precision load
SF! ( r a -- ) Single precision store
FDUP ( r -- r r )
FNIP ( ra rb -- rb )
FDROP ( r -- )
FOVER ( ra rb -- ra rb ra )
FSWAP ( ra rb -- rb ra )
F0&lt; ( r -- f )
F0= ( r -- f )
F+ ( r r -- r )
F- ( r r -- r )
F* ( r r -- r )
F/ ( r r -- r )
1/F ( r -- r )
S&gt;F ( n -- r )
F&gt;S ( r -- n )

HIGH LEVEL
----------
F= ( r r -- f )
F&lt; ( r r -- f )
F&gt; ( r r -- f )
F&lt;= ( r r -- f )
F&gt;= ( r r -- f )
F&lt;&gt; ( r r -- f )

SFLOAT ( -- 4 )
SFLOATS ( n -- n*4 )
SFLOAT+ ( a -- a+4 )
SF, ( r -- )

AFLITERAL ( r -- )
FLITERAL ( r -- ) IMMEDIATE

FCONSTANT ( r "name" )
FVARIABLE ( "name" )

PI ( -- r )

FSQRT ( r r -- r )

F.S ( -- ) Print float stack.
</pre>

<h5>Locals</h5>

<p>
Locals allow named word local parameters and values.
</p>

<pre>
Syntax:
  { local1 local2 .. -- comment }
or
  { local1 local2 .. }

Locals are ordered to match the stack, examples:
: 2OVER { a b c d } a b c d a b ;
: MAX { a b -- biggest } a b &lt; IF b ELSE a THEN ;

( Equivalent with DO and FOR )
: POW2 { n } 1 { s } n FOR AFT s 2* to s THEN NEXT s ;
: POW2 { n } 1 { s } n 0 DO s 2* to s LOOP s ;
</pre>

<p>
Capabilities and limitations:
<ul>
  <li>Support for locals referenced inside DO and FOR loops - OK</li>
  <li>Support for multiple {} uses in one definition - OK</li>
  <li>Support for TO and +TO to modify a local</li>
  <li>Locals mixed with raw return stack operations (<code>&gt;R R&gt;</code>) - NOT OK</li>
  <li>Locals defined inside a DO or FOR loop - NOT OK</li>
  <li>The low level ANSForth word <code>(LOCAL)</code> is also supported.</li>
</ul>
</p>