You're quite right. GHC has a simple but non-performant representation
of type synonyms in types, so as to be able to generate good error
messages, In particular, the type
S t
where S is a type synonym defined by 'type S a = s', is represented as
SynNote (S t) (s [t/a])
That is, (S t) is represented by *both* its un-expanded and expanded
form.
The SynNote is ignored by unification, but the un-expanded form is
useful for error messages. Unfortunately, t is duplicated, as you can
see, and that leads to the behaviour you describe.
I don't see myself fixing this soon, at least partly because I can't see
an obvious way to fix it that doesn't lose error message behaviour.
I'm going to open a SourceForge bug for it. If anyone has good ideas,
let me know.
Simon
| -----Original Message-----
| From: [EMAIL PROTECTED]
[mailto:glasgow-haskell-bugs-
| [EMAIL PROTECTED] On Behalf Of Iavor Diatchki
| Sent: 17 February 2005 01:27
| To: [email protected]
| Subject: 'type' declarations
|
| hello,
| ghc seems to be having trouble with 'type' declarations.
| while compiling (i guess kind checking is the correct word here)
| the following program for a very long time, ghc (6.2) runs out of
300Mb of heap.
|
| module Test where
|
| type S = Maybe
| type S2 n = S (S n)
| type S4 n = S2 (S2 n)
| type S8 n = S4 (S4 n)
| type S16 n = S8 (S8 n)
| type S32 n = S16 (S16 n)
|
| type N64 n = S32 (S32 n)
|
| type N64' =
| S ( S ( S ( S ( S ( S ( S ( S (
| S ( S ( S ( S ( S ( S ( S ( S (
| S ( S ( S ( S ( S ( S ( S ( S (
| S ( S ( S ( S ( S ( S ( S ( S (
| S ( S ( S ( S ( S ( S ( S ( S (
| S ( S ( S ( S ( S ( S ( S ( S (
| S ( S ( S ( S ( S ( S ( S ( S (
| S ( S ( S ( S ( S ( S ( S ( S (
| Int
| ))))))))
| ))))))))
| ))))))))
| ))))))))
| ))))))))
| ))))))))
| ))))))))
| ))))))))
|
| if i remove the N64 definition things work. i guess something
| exponential is happening
| (substitution?).
|
| -iavor
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