Sean Leather wrote:
I can see what's going on: it can't tell that the "a" I am writing there
is the same "a" that's in the type specification, but is there any way that
I can make it identify "a" with the "a" in the specification for nextPtr?
Lexically scoped type variables:
http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#scoped-type-variables
And if you require H98+FFI only, you can also use the following:
ptrSizeOf = sizeOf . asTypeOf undefined . unsafePerformIO . peek
The asTypeOf function is the H98 way of handling many scoped type
variable issues. It never evaluates its second argument so the
unsafePerformIO is perfectly safe since the peek will never be evaluated
either (and, heck, the whole argument to sizeOf won't be evaluated either).
--
Live well,
~wren
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