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Re: [Caml-list] Matching when
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Date: 2002-08-05 (16:13)
From: John Max Skaller <skaller@o...>
Subject: Re: [Caml-list] Matching when
Luc Maranget wrote:

>>What you are asking is ``pattern when expression'' to be a pattern.
>>Then your example would be parsed as
>>That is your example is to to be parsed as
>> Any              <-- pattern   | 
>>|                               | Pattern (or pat)
>> Int x when x > 0 <-- pattern   |
>>  ...             <-- right hand side
>>Modifications are really important because this would make patterns and
>>expression mutually recursive, which they are not at the moment.
The follwing code works in Felix [it prints "YES"]

#include <std.flx>

match (2,1) with
| ( (?x when x>=1), (?y when y >=1)) when x >=2 => { print "YES"; endl; }
| _ => { print "NO"; endl; }

wherein 'when' expressions are part of patterns, and as you can see,
can be nested within a pattern -- making the grammar for patterns
and expressions mutually recursive.

I'm curious as to what problems you perceive with
the mutual recursion.

John Max Skaller, mailto:skaller@ozemail.com.au
snail:10/1 Toxteth Rd, Glebe, NSW 2037, Australia.

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