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Index > Compiler Internals > [SUG] Extended syntax for 'match' directive

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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
It's not a rare occasion that sequence of match directives emulates if/else chain using some tricks. Probably match could be modified to accept the following syntax (as an example I took fragment of Win32AX.Inc pushd macro):
Code:
match {; pattern and matching sequence are both absent, that indicates alternative behavior
  =addr var,value \{; here they go
    if +var relativeto 0 | +var relativeto $
      push var
    else
      lea edx,[var]
      push edx
    end if \}
  =double [var],value \{; this will be tried only if previous pair doesn't match
    push dword [var+4]
    push dword [var] \}
  =double =ptr var,value \{; next match to try
    push dword [var+4]
    push dword [var] \}
  =double num,value \{ \local ..high,..low; you've probably got the idea
    virtual at 0
      dq num
      load ..low dword from 0
      load ..high dword from 4
    end virtual
    push ..high
    push ..low \}
  \{ \local ..continue; brace alone means final 'else'
    if value eqtype ''
      call ..continue
      db value,0
    ..continue:
    else
      push value
    end if \}
}    
As a shortcut for single if/else I think about something like this (from Win32A.Inc):
Code:
struc TCHAR [val] { common match any, val \{ . db val \} \{ . db ? \} }
; That was only to show my suggestion, I know that using default argument value, it could be reduced to
struc TCHAR [val=?] { common . db val }    
I'll research into that; meanwhile, your comments are welcome.
Post 05 Jul 2013, 07:18
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Tomasz Grysztar
Assembly Artist


Joined: 16 Jun 2003
Posts: 7709
Location: Kraków, Poland
Tomasz Grysztar
I've been thinking about some kind of elsematch directive ever since I introduced match. But I never decided on a good name for it... and since it was possible to manage (though not as elegantly) with match alone, I repeatedly dropped it from my "to do" list.

What I had in mind would look a bit like this:
Code:
match =addr var,value {
; ...
} elsematch =double [var],value {
; ...
}    
Post 05 Jul 2013, 08:36
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