title: Conditional compilation
description:

 So far, let this message be here. Probably later I will
 write something better (mlg).


 Subject: Re: Conditional compilation
 Date: Fri, 26 Oct 2001 01:48:52 +0400
 From: "Michael L.Gassanenko" <m_l_g3@yahoo.com>
 Organization: St.Petersburg University
 Newsgroups: comp.lang.forth

Jeff Penn wrote:
>
> I have been cleaning up an application which uses conditional compilation.
> To avoid [IF]/[ELSE]/[THEN] from cluttering up source files I use a 'make'
> file to compile the application:
>
> \ ** Options section **
> TRUE  CONSTANT i
> i 0=  CONSTANT j  \ i and j mutually exclusive
> FALSE CONSTANT k
>
> \ ** Compilation section **
>
> [UNDEFINED] tools  [IF]  INCLUDE tools.4  [THEN]
>
> j  [IF]  INCLUDE appa.4  [THEN]
>
> i  [IF]  INCLUDE appi.4  INCLUDE appx.4
> [ELSE]
>   k  [IF]  INCLUDE appjk.4  INCLUDE appy.4
>   [ELSE]   INCLUDE appj.4  INCLUDE appx.4
>   [THEN]
> [THEN]
>
> This clutters up the compilation section of the make file.
>
> Using a technique suggested in the "Forth Programmer's Handbook" I came up
> with this:
>
> \ ** Options section **
> TRUE               CONSTANT i  \ j if FALSE
> FALSE i INVERT AND CONSTANT k
>
> : \def?   ( -- )  POSTPONE [DEFINED]  IF POSTPONE \ THEN  ; IMMEDIATE
> : \-def?  ( -- )  POSTPONE [UNDEFINED]  IF POSTPONE \ THEN  ; IMMEDIATE
>
> : \i  ( -- )  i INVERT  IF  POSTPONE \  THEN  ; IMMEDIATE
> : \j  ( -- )  i         IF  POSTPONE \  THEN  ; IMMEDIATE
>
> : \k   ( -- )  k INVERT  IF  POSTPONE \  THEN  ; IMMEDIATE
> : \-k  ( -- )  k         IF  POSTPONE \  THEN  ; IMMEDIATE
>
> \ ** Compilation section **
>
> \def? tools  INCLUDE tools.4
>
> \j     INCLUDE appa.4
>
> \i     INCLUDE appi.4
> \j \-k INCLUDE appj.4
> \j \k  INCLUDE appjk.4
>    \-k INCLUDE appx.4
> \j \k  INCLUDE appy.4
>
> Which unclutters the compilation section, at the expense of the options
> section.
>
> Is this more readable?.
>
> Is there a better way to define \i \j \k & \-k which isn't too complicated?.

1) When I see \i , I think: is it skip-if-i-is-true,
or is it do-if-i-is-true-else-skip ?

I used names like board: and pc: .

: OPTION
     CREATE , IMMEDIATE DOES> @ 0= IF [COMPILE] \ THEN
;

FALSE OPTION pc:
TRUE  OPTION brd:
TRUE  OPTION dbg:

More complicated:

: OPTIONS
    DUP OPTION 0= OPTION
;

FALSE OPTIONS pc:  ~pc:
TRUE  OPTIONS brd: ~brd:
TRUE  OPTIONS dbg: ~dbg:

Or, alternatively:

: ~
    ' >BODY @ IF [COMPILE] \ THEN
; IMMEDIATE

  pc:  ~ dbg:     INCLUDE ...
~ pc:  ~ dbg:     INCLUDE ...

2) the notation like

  pc:   dbg:     INCLUDE fn1
  brd:  dbg:     INCLUDE fn2

is indeed more readable.

 -- --
I used this scheme in real projects, and what followed
things like dbg: was not INCLUDEs. There were magic numbers,
code fragments, etc., but I do not remember any INCLUDEs.

 -- --
 disclaimer:
I used definitions like

 : pc: [COMPILE] \ ; IMMEDIATE
 \ : pc:             ; IMMEDIATE

and did not try the code that I posted here.

Best regards, Michael Gassanenko
 --
the right question is half the answer