Forth Programmer’s Handbook
Longer constructs should be structured like this:
<code to generate flag>__if
___<true clause> then
<code to generate flag>__if
___<true clause> else
___<false clause> then
6.2.4 do…loop Structures
In do…loop constructs that occupy no more than one line, two spaces should be used both before and after each do or loop.
<code to calculate limits>__do__xxx__loop__
Longer constructs should be structured like this:
<code to calculate limits>__do
___<body> loop
The longer +loop constructs should be structured like this:
<code to calculate limits>__do
___<body>
<incremental value>_+loop
6.2.5 begin…while…repeat Structures
In begin…while…repeat constructs that occupy that occupy no more than one line, two spaces should be used both before and after each begin, while, or repeat.
__begin__<flag code>__while__<body>__repeat__
188 Programming Style
Forth Programmer’s Handbook
Longer constructs:
begin__<short flag code>__while
___<body> repeat begin
___<long flag code> while
___<body> repeat
6.2.6 begin…until…again Structures
In begin…until and begin…again constructs that occupy no more than one line, two spaces should be used both before and after each begin, until, or again.
__begin__<body>__until __begin__<body>__again
Longer constructs:
begin
___<body> until begin
___<body> again
6.2.7 Block Comments
Block comments begin with \_. All text after the space is ignored until after the next new line. It would be possible to delimit block comments with parentheses, but the use of parentheses is reserved by convention for stack comments.
Precede each non-trivial definition with a block comment giving a clear and concise explanation of what the word does. Put more comments at the very
Programming Style 189
Forth Programmer’s Handbook
beginning of the file to describe external words which could be used from the User Interface.
6.2.8 Stack Comments
Stack comments begin with (_ and end with ). Use stack liberally within definitions. Try to structure each definition so that, when you put stack comments at the end of each line, the stack picture makes a nice pattern.
: name (stack before -- stack after)
___xxx xxx bar ( stack condition after the execution of bar)
___xxx xxx foo ( stack condition after the execution of foo)
___xxx xxx dup ( stack condition after the execution of dup)
6.2.9 Return Stack Comments
Return stack comments are also delimited with parentheses. In addition, the notation r: is used at the beginning of the return stack comment to differentiate it from a data stack comment.
Place return stack comments on any line that contains one or more words that cause the return stack to change. (This limitation is a practical one; it is often difficult to do otherwise due to lack of space.) The words >r and r> must be paired inside colon definitions and inside do…loop constructs.
: name ( stack before -- stack after )
___xxx >r ( r:addr )
___xxx r> ( r: )
6.2.10 Numbers
Hexadecimal numbers should be typed in a lower case. If a given number contains more the four digits, the number may be broken into groups of four digits with periods. For example:
190 Programming Style