[mercury-users] map__foldl2

Fergus Henderson fjh at cs.mu.OZ.AU
Thu Dec 16 23:04:32 AEDT 1999

On 14-Dec-1999, Warwick Harvey <wharvey at cs.monash.edu.au> wrote:
> Unfortunately, it seems one cannot do this kind of wrapping trick with 
> higher-order predicates if you want the result to work in multiple modes.  
> :-(

Yes, for that to work nicely, we'd need to be able to infer the modes
for higher-order terms, and for various reasons which have been discussed
on this list long ago, that's not easy.

There is a work-around, but it's not very elegant.  For an example,
see the code in the implementation section of library/exception.m,
where the multi-moded higher-order predicate `try' is implemented as a
wrapper around the multi-moded higher-order predicate `builtin_catch'.

Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at        |     -- the last words of T. S. Garp.
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