File:  [gforth] / gforth / compat / assert.fs
Revision 1.1: download - view: text, annotated - select for diffs
Wed Apr 29 17:09:46 1998 UTC (24 years, 2 months ago) by anton
Branches: MAIN
CVS tags: v0-7-0, v0-6-2, v0-6-1, v0-6-0, v0-5-0, v0-4-0, HEAD
tables are in the image again
added assert.fs defer.fs exception.fs vocabulary.fs to the compat directory

    1: \ assertions
    2: 
    3: \ This file is in the public domain. NO WARRANTY.
    4: 
    5: \    It is a good idea to make your programs self-checking, in
    6: \ particular, if you use an assumption (e.g., that a certain field of a
    7: \ data structure is never zero) that may become wrong during maintenance.
    8: \ Gforth supports assertions for this purpose. They are used like this:
    9: 
   10: \      assert( FLAG )
   11: 
   12: \    The code between `assert(' and `)' should compute a flag, that
   13: \ should be true if everything is alright and false otherwise. It should
   14: \ not change anything else on the stack. The overall stack effect of the
   15: \ assertion is `( -- )'. E.g.
   16: 
   17: \      assert( 1 1 + 2 = ) \ what we learn in school
   18: \      assert( dup 0<> ) \ assert that the top of stack is not zero
   19: \      assert( false ) \ this code should not be reached
   20: 
   21: \    The need for assertions is different at different times. During
   22: \ debugging, we want more checking, in production we sometimes care more
   23: \ for speed. Therefore, assertions can be turned off, i.e., the assertion
   24: \ becomes a comment. Depending on the importance of an assertion and the
   25: \ time it takes to check it, you may want to turn off some assertions and
   26: \ keep others turned on. Gforth provides several levels of assertions for
   27: \ this purpose:
   28: 
   29: \ `assert0('       --         gforth       ``assert-zero''
   30: \    important assertions that should always be turned on
   31: 
   32: \ `assert1('       --         gforth       ``assert-one''
   33: \    normal assertions; turned on by default
   34: 
   35: \ `assert2('       --         gforth       ``assert-two''
   36: \    debugging assertions
   37: 
   38: \ `assert3('       --         gforth       ``assert-three''
   39: \    slow assertions that you may not want to turn on in normal debugging;
   40: \ you would turn them on mainly for thorough checking
   41: 
   42: \ `assert('       --         gforth       ``assert(''
   43: \    equivalent to assert1(
   44: 
   45: \ `)'       --         gforth       ``close-paren''
   46: \    end an assertion
   47: 
   48: \    `Assert(' is the same as `assert1('. The variable `assert-level'
   49: \ specifies the highest assertions that are turned on. I.e., at the
   50: \ default `assert-level' of one, `assert0(' and `assert1(' assertions
   51: \ perform checking, while `assert2(' and `assert3(' assertions are
   52: \ treated as comments.
   53: 
   54: \    Note that the `assert-level' is evaluated at compile-time, not at
   55: \ run-time. I.e., you cannot turn assertions on or off at run-time, you
   56: \ have to set the `assert-level' appropriately before compiling a piece
   57: \ of code. You can compile several pieces of code at several
   58: \ `assert-level's (e.g., a trusted library at level 1 and newly written
   59: \ code at level 3).
   60: 
   61: \ `assert-level'       -- a-addr         gforth       ``assert-level''
   62: \    all assertions above this level are turned off
   63: 
   64: \ The program uses the following words
   65: \ from CORE :
   66: \ Variable ! : @ > IF POSTPONE THEN ; immediate 0= 
   67: \ from BLOCK-EXT :
   68: \ \ 
   69: \ from EXCEPTION-EXT :
   70: \ abort" 
   71: \ from FILE :
   72: \ ( 
   73: 
   74: variable assert-level ( -- a-addr ) \ gforth
   75: \ all assertions above this level are turned off
   76: 1 assert-level !
   77: 
   78: : assertn ( n -- ) \ gforth assert-n
   79:     \ this is internal (it is not immediate)
   80:     assert-level @ >
   81:     if
   82: 	POSTPONE (
   83:     then ;
   84: 
   85: : assert0( ( -- ) \ gforth assert-zero
   86:     \ important assertions that should always be turned on
   87:     0 assertn ; immediate
   88: : assert1( ( -- ) \ gforth assert-one
   89:     \ normal assertions; turned on by default
   90:     1 assertn ; immediate
   91: : assert2( ( -- ) \ gforth assert-two
   92:     \ debugging assertions
   93:     2 assertn ; immediate
   94: : assert3( ( -- ) \ gforth assert-three
   95:     \ slow assertions that you may not want to turn on in normal debugging;
   96:     \ you would turn them on mainly for thorough checking
   97:     3 assertn ; immediate
   98: : assert( ( -- ) \ gforth
   99:     \ equivalent to assert1(
  100:     POSTPONE assert1( ; immediate
  101: 
  102: : (endassert) ( flag -- ) \ gforth-internal
  103:     \ inline argument sourcepos
  104:     0= abort" assertion failed" ;
  105: 
  106: : ) ( -- ) \ gforth	close-paren
  107:     \ end an assertion
  108:     POSTPONE (endassert) ; immediate

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