[mercury-users] discriminated union question

[Peter Ross]

On Wed, Apr 11, 2001 at 04:52:57PM -0400, Terrence Brannon wrote:
> :- type pair(T1, T2)
>         --->    T1 - T2.
> 
> What is the "-" sign doing here? What does it mean? It doesn't mean
> subtraction does it?
> 
The Mercury parser converts T1 - T2 to '-'(T1, T2) which is valid term.
In other words the infix operators are just syntactic sugar.

Later on the type checker will decide from context whether the term is
the function '-'(A,B) which subtracts two numbers or the constructor
'-'(A,B) for a data term.

Hope this helps,
Pete
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