[mercury-users] Pred defns

Lee Naish lee at cs.mu.OZ.AU
Fri Apr 3 17:43:38 AEST 1998

Peter Schachte wrote:
>On Fri, 3 Apr 1998, Lee Naish wrote:
>> Perhaps Peter would prefer it if postfix operator were used as I
>> suggested (to emphasise the accumulator id rather than the syntactic
>> gloop).  There is an added advantage with ':=' - the accumulator id is
>> on the left of the assignment operator, like most languages, eg:
>> 	map__set(map#, Key1, Value1, map#:=),
>But since map# and := sensible separate things, it would be tempting to
>leave a space between the # and the :=, leading to nothing good.

This argument can be leveled at pretty much every operator with more
than one character.  After a few syntax error messages I think most
programmers would get the hang of it.

>when you do an assignment, you'd /need/ to leave a space between the # and
>the := or nothing good would come of it.  I find this more worrying. 

I'm not sure its good to have a special := construct as well as a
general update accumulator construct - the general purpose one alone is
probably better.  I think a := construct will confuse novices a great
deal - they will try to use it to assign to variables (perhaps I'm being
unduely influenced by my current teaching load :-).


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