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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Using a string as a binary operator
Newsgroups: comp.lang.ada
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Date: Thu, 16 Oct 2008 10:14:28 +0200
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Date: 2008-10-16T10:14:28+02:00
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On Wed, 15 Oct 2008 08:22:36 -0700 (PDT), Adam Beneschan wrote:

> Although it isn't always possible, I definitely prefer to set things
> up in an array or some sort of data structure when possible, rather
> than to rely on a 67-branch IF statement or even a CASE statement.

This is what I do in my parsers. I use an enumeration type for the
operations. For example:

   type Operations is
           (  Add, Sub, Mul, Div, Pow,    -- Infix operators
              Abs_Value, Plus, Minus,     -- Prefix operators
              Left_Bracket, Right_Bracket -- Brackets
           );

When the parser pops an operation from the stack of operations it calls the
corresponding primitive operation (of the stack type) that switches over
Operations value using plain case statement.

I don't define unary and binary operations separately, because with
subprograms supported the number of arguments will vary anyway. Then even
for +, I prefer to allow the parser to coalesce expressions like

  "+" ("+" (A, B), C)

into

  "+" (A, B, C)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de