* Daniel Trstenjak
Hi Roman,
One issue with it in Haskell is that it'd lead to inconsistent semantics:
myEq x x = True
is not the same as
myEq x y = case y of x -> True
I don't think that it's inconsistent, because the 'case' defines a new name scope, like the function does for its arguments.
One should interpret consecutive function arguments as being in the nested scopes, too, rather than in one flat scope. Otherwise, in x = 2 f x ((x ==) -> True) = True the 'x' in the view pattern would refer to the global x, rather than the function parameter. (And it would, indeed, if you swap the patterns.) The same applies to scoped type variables. (Haskell2010 does not have either of these extensions, so there the two interpretations — nested scopes and one flat scope — are equivalent.)
Otherwise you would also expect a different behavior for:
x = 2
myEq x x = True
In fact, lots of Haskell newcomers are surprised that f 10 = 42 is not the same as n = 10 f n = 42 And this proposal further reinforces the impression that pattern-matching against a bound variable is interpreted as an equality test. Roman