#5910: Holes with other constraints
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Reporter: xnyhps | Owner:
Type: feature request | Status: new
Priority: high | Milestone: 7.8.1
Component: Compiler (Type checker) | Version: 7.5
Keywords: holes | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Other
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonpj@…):
commit 8a9a7a8c42da3adb603f319a74e304af5e1b2128
{{{
Author: Simon Peyton Jones <simo...@microsoft.com>
Date: Mon Sep 17 13:31:14 2012 +0100
Add type "holes", enabled by -XTypeHoles, Trac #5910
This single commit combines a lot of work done by
Thijs Alkemade <thijsalkem...@gmail.com>, plus a slew
of subsequent refactoring by Simon PJ.
The basic idea is
* Add a new expression form "_", a hole, standing for a not-yet-
written expression
* Give a useful error message that
(a) gives the type of the hole
(b) gives the types of some enclosing value bindings that
mention the hole
Driven by this goal I did a LOT of refactoring in TcErrors, which in
turn
allows us to report enclosing value bindings for other errors, not
just
holes. (Thijs rightly did not attempt this!)
The major data type change is a new form of constraint
data Ct = ...
| CHoleCan {
cc_ev :: CtEvidence,
cc_hole_ty :: TcTauType,
cc_depth :: SubGoalDepth }
I'm still in two minds about whether this is the best plan. Another
possibility would be to have a predicate type for holes, somthing like
class Hole a where
holeValue :: a
It works the way it is, but there are some annoying special cases for
CHoleCan (just grep for "CHoleCan").
compiler/deSugar/Coverage.lhs | 1 +
compiler/deSugar/DsExpr.lhs | 2 +
compiler/hsSyn/HsExpr.lhs | 3 +
compiler/main/DynFlags.hs | 4 +-
compiler/rename/RnExpr.lhs | 11 +-
compiler/typecheck/Inst.lhs | 31 ++--
compiler/typecheck/TcBinds.lhs | 90 ++++----
compiler/typecheck/TcCanonical.lhs | 9 +-
compiler/typecheck/TcEnv.lhs | 21 ++-
compiler/typecheck/TcErrors.lhs | 443
++++++++++++++++++++++--------------
compiler/typecheck/TcExpr.lhs | 9 +
compiler/typecheck/TcHsSyn.lhs | 3 +
compiler/typecheck/TcMType.lhs | 14 +-
compiler/typecheck/TcRnMonad.lhs | 35 ++-
compiler/typecheck/TcRnTypes.lhs | 96 +++++---
compiler/typecheck/TcRules.lhs | 28 ++-
compiler/typecheck/TcSMonad.lhs | 36 ++--
compiler/typecheck/TcSimplify.lhs | 110 ++++------
compiler/typecheck/TcUnify.lhs | 2 -
compiler/types/Type.lhs | 18 +-
20 files changed, 565 insertions(+), 401 deletions(-)
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5910#comment:21>
GHC <http://www.haskell.org/ghc/>
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