Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!tut.cis.ohio-state.edu!ukma!ukecc!agollum
From: agollum@engr.uky.edu (Kenneth Herron)
Newsgroups: comp.lang.pascal
Subject: Re: Procedures or Functions as parameters
Summary: Here's a way
Message-ID: <2425@ukecc.engr.uky.edu>
Date: 10 Jun 88 04:53:09 GMT
References: <213@lafcol.UUCP> <2165@ucdavis.ucdavis.edu> <1240@csuna.UUCP>
Reply-To: agollum@engr.uky.edu (Kenneth Herron)
Followup-To: comp.lang.pascal
Distribution: na
Organization: Way down south in the land of Basketball
Lines: 58

>>>Has anyone tried to pass procedures or functions as parameters within
>>>user written procedures? 
>If you
>look carefully at the manual for Turbo (Appendix B p 532) you'll see it
>clearly stated that procedural or functional parameters are not allowed
>in Turbo.

(Actually it's page 520)

Well, the database toolbox SORT unit manages it.  It's kinda tricky
though...let's see how well I can describe it without violating their
copyright on the source code :-)

1) Define your procedures/functions like this:

{$F+}  {this is required}
Procedure Foo;
begin
[...]
end; {foo}

Function Bar(var X, Y: byte): boolean;
begin
[...]
end; {bar}
{$F-}

2) Declare a pointer like this
   var
      GluePtr: Pointer;  { generic pointer type }

3) Declare a function or procedure like this, with GluePtr declared
   outside it:
 
{$F+}
procedure CallProc;
inline($FF/$1E/GluePtr);  {CALL DWORD PTR GluePtr}
 
function CallFunc(var x, y: byte):boolean;
inline($FF/$1E/GluePtr);  {CALL DWORD PTR GluePtr}
{$F-}

   Note the actual parameter list should exactly match the parameter
   list of the function/procedure pointed to by GluePtr.
   You'll need to declare a different CallProc (with different names,
   natch) for a procedure with a different paramater list.  Same for
   CallFunc.

4) Call the darn thing like this:

GluePtr := @Foo;   {Foo is a procedure with no arguments}
CallProc;          {Foo will be executed}

GluePtr := @Bar;   {Bar is a procedure with two byte args, boolean return}
if CallFunc(x,y) then...

For a more real-world example, check out the toolbox.

Kenneth Herron