Louis Wasserman wrote:
I'd like to see something resembling as-patterns in type signatures.
Specifically, there are cases where I'm inclined to use
(m ~ pat) in a type context when m isn't otherwise constrained, just so I
can use m as an abbreviation for pat. To reduce these cases, I'd like to
see the syntax m...@pat allowed for use in type signatures, with m becoming
simply an alias for pat. Thoughts?
I've added a ticket here <http://hackage.haskell.org/trac/ghc/ticket/3545>.
+1.
I've often wanted this when doing type-level programming. Another nice
thing this suggests is the ability to use underscore as a pattern for
when you know the compiler will infer the type but it's too complex to
want to write out (e.g. while experimenting). With x...@_ you could even
share the complex type in multiple places, since x will be bound to some
actual type rather than being universally quantified. (Of course, ISTR
someone's suggested the underscores in the past and had it rejected. Alas.)
--
Live well,
~wren
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