On Wed, Sep 2, 2009 at 11:24 PM, aditya siram
Hi all, Recently I wrote a function that takes a unique identifier that I called 'id'. I then tried to apply the 'id' function to it and GHC did not like that. But it should.
For example in 'test' I have told the compiler that the id argument is an Int. So type inference should be able to determine the first 'id' in 'id id' couldn't possibly be an Int, but it complains. So I explicitly told the compiler the type of 'id' in test1 - this didn't work either. The final function 'test3' works as expected. Is there something I am not understand about the way type inference is supposed to work?
test :: Int -> Int test id = id id
test1 :: Int -> Int test1 id = idFunc id where idFunc :: a -> a idFunc = id
test2 :: Int -> Int test2 myid@id = id myid
test3 :: Int -> Int test3 id = Prelude.id id
How is the compiler supposed to differentiate between the situation where you really mean `id id` (and it type checks properly) and where you've mistakenly written `id id` (but it doesn't type check)? If that doesn't make you realise then think of it as your `id` shadowing the Prelude's, and that happens irrespective of the types. /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe