diff options
| author | Simon Peyton Jones <simonpj@microsoft.com> | 2017-09-21 17:35:11 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2017-09-25 11:07:23 +0100 |
| commit | 3c74a51232813eb733b27c43c94ce005112a0ddb (patch) | |
| tree | 2b571b2641f76166f74c3c7601d649267387c3d1 /compiler/prelude/TysWiredIn.hs | |
| parent | b3ae47caf2f23cfd2c22c29dbfca646493ffe469 (diff) | |
| download | haskell-3c74a51232813eb733b27c43c94ce005112a0ddb.tar.gz | |
Deal with large extra-contraints wildcards
For reasons explained in TcHsType
Note [Extra-constraint holes in partial type signatures],
if we had
f :: (_) => blahs
and the '_' was filled in by more than a 62-tuple of contraints,
GHC crashed.
The same Note explains the hacky solution I have adopted to
evade this. Maybe there is some better way, but I couldn't
see one that didn't involve a great deal of work. And the problem
is a very narrow one! If the hack bites us we'll need to think
again.
Diffstat (limited to 'compiler/prelude/TysWiredIn.hs')
| -rw-r--r-- | compiler/prelude/TysWiredIn.hs | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/compiler/prelude/TysWiredIn.hs b/compiler/prelude/TysWiredIn.hs index f4e055f376..01579830f8 100644 --- a/compiler/prelude/TysWiredIn.hs +++ b/compiler/prelude/TysWiredIn.hs @@ -621,12 +621,13 @@ Note [How tuples work] See also Note [Known-key names] in PrelNames - Given constraints: the superclasses automatically become available - Wanted constraints: there is a built-in instance instance (c1,c2) => (c1,c2) - - Currently just go up to 16; beyond that + See TcInteract.matchCTuple + - Currently just go up to 62; beyond that you have to use manual nesting - Their OccNames look like (%,,,%), so they can easily be distinguished from term tuples. But (following Haskell) we - pretty-print saturated constraint tuples with round parens; see - BasicTypes.tupleParens. + pretty-print saturated constraint tuples with round parens; + see BasicTypes.tupleParens. * In quite a lot of places things are restrcted just to BoxedTuple/UnboxedTuple, and then we used BasicTypes.Boxity to distinguish |