On Aug 23, 2012, at 10:32 PM, wren ng thornton wrote:
Now, be careful of something here. The reason this fails is because we're
compiling Haskell to System Fc, which is a Church-style lambda calculus
(i.e., it explicitly incorporates types into the term language). It is this
fact of being
System Fc has another name: GHC Core. You can read it by running 'ghc
-ddump-ds' (or, if you want to see the much later results after
optimization, -ddump-simpl):
For example:
NonGADT.hs:
{-# LANGUAGE TypeFamilies, ExistentialQuantification, GADTs #-}
module NonGADT where
data T a = (a ~ ())
On 8/22/12 5:23 PM, Matthew Steele wrote:
So my next question is: why does unpacking the newtype via pattern matching
suddenly limit it to a single monomorphic type?
Some Haskell code:
foo :: (forall a. a - Int) - Bool
foo fn = ...
newtype IntFn a = IntFn (a - Int)
bar1 ::
| This compiles just fine, as I would expect. But now let's say I want
| to change it to make IntFn a newtype:
|
| newtype IntFn a = IntFn (a - Int)
|
| bar :: (forall a. (FooClass a) = IntFn a) - Bool
| bar (IntFn fn) = foo fn
The easiest way is to imagine transforming the
Quoting Matthew Steele mdste...@alum.mit.edu:
{-# LANGUAGE Rank2Types #-}
class FooClass a where ...
foo :: (forall a. (FooClass a) = a - Int) - Bool
foo fn = ...
newtype IntFn a = IntFn (a - Int)
bar :: (forall a. (FooClass a) = IntFn a) - Bool
bar (IntFn fn)
On Aug 22, 2012, at 3:02 PM, Lauri Alanko wrote:
Quoting Matthew Steele mdste...@alum.mit.edu:
{-# LANGUAGE Rank2Types #-}
class FooClass a where ...
foo :: (forall a. (FooClass a) = a - Int) - Bool
foo fn = ...
newtype IntFn a = IntFn (a - Int)
bar :: (forall
On Wed, Aug 22, 2012 at 10:13 PM, Matthew Steele mdste...@alum.mit.edu wrote:
On Aug 22, 2012, at 3:02 PM, Lauri Alanko wrote:
Quoting Matthew Steele mdste...@alum.mit.edu:
{-# LANGUAGE Rank2Types #-}
class FooClass a where ...
foo :: (forall a. (FooClass a) = a - Int) - Bool
Quoting Matthew Steele mdste...@alum.mit.edu:
1) bar ifn = case ifn of IntFn fn - foo fn
2) bar ifn = foo (case ifn of IntFn fn - fn)
I can't help feeling like maybe I am missing some small but
important piece from my mental model of how rank-2 types work.
As SPJ suggested, translation to
On Aug 22, 2012, at 4:32 PM, Erik Hesselink wrote:
On Wed, Aug 22, 2012 at 10:13 PM, Matthew Steele mdste...@alum.mit.edu
wrote:
On Aug 22, 2012, at 3:02 PM, Lauri Alanko wrote:
Quoting Matthew Steele mdste...@alum.mit.edu:
{-# LANGUAGE Rank2Types #-}
class FooClass a where ...
