Re: Semantics of Irrefutable Pattern Matching

[Simon L Peyton Jones]

Namrata asks...

| So, when x1' + x2' is evaluated,
| Is (1,2) pattern matched against (a,b) twice -- once for x1' and once
| for x2' ??

The translation you give (correctly I think) expresses the required
*semantics*.  But the translation is not the required *implementation*.  A
compiler can do anything to improve runtime, provided it maintains the
defined semantics.  In particular, a good compiler will spot the optimsation
you indicate, and match only once.

Simon