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author | Simon Peyton Jones <simonpj@microsoft.com> | 2012-06-13 17:21:09 +0100 |
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committer | Simon Peyton Jones <simonpj@microsoft.com> | 2012-06-13 17:21:09 +0100 |
commit | 5a8ac0f823c151c062a3f1903574030423bb255c (patch) | |
tree | 60c7bbe1091ddba9c404f8024928fcea83480523 /compiler/ghc.cabal.in | |
parent | 03f78f0686f048e75d671f2797c8684b71655c49 (diff) | |
download | haskell-5a8ac0f823c151c062a3f1903574030423bb255c.tar.gz |
Simplify the implementation of Implicit Parameters
This patch re-implements implicit parameters via a class
with a functional dependency:
class IP (n::Symbol) a | n -> a where
ip :: a
This definition is in the library module GHC.IP. Notice
how it use a type-literal, so we can have constraints like
IP "x" Int
Now all the functional dependency machinery works right to make
implicit parameters behave as they should.
Much special-case processing for implicit parameters can be removed
entirely. One particularly nice thing is not having a dedicated
"original-name cache" for implicit parameters (the nsNames field of
NameCache). But many other cases disappear:
* BasicTypes.IPName
* IPTyCon constructor in Tycon.TyCon
* CIPCan constructor in TcRnTypes.Ct
* IPPred constructor in Types.PredTree
Implicit parameters remain special in a few ways:
* Special syntax. Eg the constraint (IP "x" Int) is parsed
and printed as (?x::Int). And we still have local bindings
for implicit parameters, and occurrences thereof.
* A implicit-parameter binding (let ?x = True in e) amounts
to a local instance declaration, which we have not had before.
It just generates an implication contraint (easy), but when
going under it we must purge any existing bindings for
?x in the inert set. See Note [Shadowing of Implicit Parameters]
in TcSimplify
* TcMType.sizePred classifies implicit parameter constraints as size-0,
as before the change
There are accompanying patches to libraries 'base' and 'haddock'
All the work was done by Iavor Diatchki
Diffstat (limited to 'compiler/ghc.cabal.in')
-rw-r--r-- | compiler/ghc.cabal.in | 1 |
1 files changed, 0 insertions, 1 deletions
diff --git a/compiler/ghc.cabal.in b/compiler/ghc.cabal.in index bfd44384bb..4371bca95e 100644 --- a/compiler/ghc.cabal.in +++ b/compiler/ghc.cabal.in @@ -404,7 +404,6 @@ Library TcCanonical TcSMonad Class - IParam Coercion FamInstEnv FunDeps |