[mercury-users] overloading predicates/functions

[Fergus Henderson]

On 03-Oct-1999, Michael Day <mikeday at corplink.com.au> wrote:
> 
> Is it possible to overload predicates or functions in Mercury by the type
> of their arguments, as well as the arity?

Yes, so long as the predicates or functions in question reside in
different modules, or different sub-modules.

> If not, how do people normally cope with functions that need to take
> several possible types, but not *every* possible type? By creating
> multiple names with suffixes like _float, _string, etc?

There's three alternatives:

	- use multiple names with suffixes
	  (e.g. io__write_string, io__write_float in library/io.m)

	- use ad-hoc overloading, and put overloaded versions
	  that would have the same module, name, and arity
	  into sub-modules
	  (e.g. see extras/complex_numbers)

	- use type classes

-- 
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 128.250.37.3        |     -- the last words of T. S. Garp.
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