#2431: Allow empty case analysis
-------------------------------------------+--------------------------------
Reporter: RalfHinze | Owner:
Type: feature request | Status: closed
Priority: low | Milestone: _|_
Component: Compiler | Version: 6.8.3
Resolution: fixed | Keywords: empty case
analysis
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Difficulty: Unknown
Testcase: deSugar/should_compile/T2431 | Blockedby:
Blocking: | Related:
-------------------------------------------+--------------------------------
Changes (by simonpj):
* status: new => closed
* testcase: => deSugar/should_compile/T2431
* resolution: => fixed
Comment:
Here it is:
{{{
commit 3671e674757c8f82ec1f0ea9b7c1ed56340b55bc
Author: Simon Peyton Jones <[email protected]>
Date: Fri Jan 4 10:27:38 2013 +0000
Allow empty case expressions (and lambda-case) with -XEmptyCase
The main changes are:
* Parser accepts empty case alternatives
* Renamer checks that -XEmptyCase is on in that case
* (Typechecker is pretty much unchanged.)
* Desugarer desugars empty case alternatives, esp:
- Match.matchWrapper and Match.match now accept empty eqns
- New function matchEmpty deals with the empty case
- See Note [Empty case alternatives] in Match
This patch contains most of the work, but it's a bit mixed up
with a refactoring of MatchGroup that I did at the same time
(next commit).
compiler/deSugar/DsExpr.lhs | 13 +-------
compiler/deSugar/DsUtils.lhs | 2 +-
compiler/deSugar/Match.lhs | 55
++++++++++++++++++++++++++++---------
compiler/deSugar/MatchCon.lhs | 3 +-
compiler/deSugar/MatchLit.lhs | 2 +-
compiler/main/DynFlags.hs | 4 ++-
compiler/parser/Parser.y.pp | 2 +
compiler/rename/RnBinds.lhs | 18 ++++++++++--
docs/users_guide/glasgow_exts.xml | 38 +++++++++++++++++++++++++
9 files changed, 106 insertions(+), 31 deletions(-)
}}}
but it also needs the follow up
{{{
commit a8941e2a4fe3b000e6c085701e0c015c5316c6ee
Author: Simon Peyton Jones <[email protected]>
Date: Fri Jan 4 10:30:14 2013 +0000
Refactor HsExpr.MatchGroup
* Make MatchGroup into a record, and use the record fields
* Split the type field into two: mg_arg_tys and mg_res_ty
This makes life much easier for the desugarer when the
case alterantives are empty
A little bit of this change unavoidably ended up in the preceding
commit about empty case alternatives
compiler/deSugar/Coverage.lhs | 12 ++++++------
compiler/deSugar/DsArrows.lhs | 13 ++++++-------
compiler/deSugar/DsExpr.lhs | 8 ++++----
compiler/deSugar/DsGRHSs.lhs | 14 +++++++-------
compiler/deSugar/DsMeta.hs | 10 +++++-----
compiler/hsSyn/HsExpr.lhs | 28 +++++++++++++---------------
compiler/hsSyn/HsUtils.lhs | 2 +-
compiler/parser/RdrHsSyn.lhs | 8 ++++----
compiler/rename/RnBinds.lhs | 4 ++--
compiler/rename/RnExpr.lhs | 2 +-
compiler/rename/RnTypes.lhs | 2 +-
compiler/typecheck/TcArrows.lhs | 9 ++++++---
compiler/typecheck/TcBinds.lhs | 4 ++--
compiler/typecheck/TcHsSyn.lhs | 7 ++++---
compiler/typecheck/TcMatches.lhs | 14 ++++++++------
15 files changed, 70 insertions(+), 67 deletions(-)
}}}
and
{{{
commit 74d401860d6a28244b9a12fca844fe14a6a04274
Author: Simon Peyton Jones <[email protected]>
Date: Fri Jan 4 10:30:53 2013 +0000
Switch on -XEmptyCase when renaming derived declarations
Compiler-generated code can have empty cases
>---------------------------------------------------------------
compiler/typecheck/TcDeriv.lhs | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2431#comment:14>
GHC <http://www.haskell.org/ghc/>
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