#2102: Typeclass membership doesn't bring coercion superclass requirements into
scope
-------------------------------------------------+--------------------------
Reporter: ryani | Owner: chak
Type: bug | Status: closed
Priority: low | Milestone: 7.2.1
Component: Compiler (Type checker) | Version: 7.1
Resolution: fixed | Keywords: superclass
equalities
Testcase: indexed_types/should_compile/T2102 | Blockedby:
Difficulty: Unknown | Os:
Unknown/Multiple
Blocking: | Architecture:
Unknown/Multiple
Failure: Compile-time crash |
-------------------------------------------------+--------------------------
Changes (by simonpj):
* status: new => closed
* testcase: => indexed_types/should_compile/T2102
* resolution: => fixed
Comment:
Hurrah! We now have superclass equalities. I've added this example as a
test.
{{{
commit 940d1309e58382c889c2665227863fd790bdb21c
Author: Simon Peyton Jones <simo...@microsoft.com>
Date: Wed Jun 22 17:37:47 2011 +0100
Add equality superclasses
Hurrah. At last we can write
class (F a ~ b) => C a b where { ... }
This fruit of the fact that equalities are now values,
and all evidence is handled uniformly.
The main tricky point is that when translating to Core
an evidence variable 'v' is represented either as
either Var v
or Coercion (CoVar v)
depending on whether or not v is an equality. This leads
to a few annoying calls to 'varToCoreExpr'.
compiler/basicTypes/MkId.lhs | 4 +-
compiler/deSugar/DsExpr.lhs | 18 +++++++-
compiler/iface/BuildTyCl.lhs | 50 ++++++++++------------
compiler/typecheck/TcInstDcls.lhs | 85
+++++++++++++++++-------------------
compiler/typecheck/TcMType.lhs | 9 +----
compiler/types/Class.lhs | 21 ++++------
6 files changed, 92 insertions(+), 95 deletions(-)
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2102#comment:14>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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