Commit 2346de44 authored by eir@cis.upenn.edu's avatar eir@cis.upenn.edu

Fix #1476 by making splice patterns work.

Unfortunately, splice patterns in brackets still do not work
because we don't run splices in brackets. Without running a pattern
splice, we can't know what variables it binds, so we're stuck.

This is still a substantial improvement, and it may be the best
we can do. Still must document new behavior.
parent d627c5cf
......@@ -440,10 +440,12 @@ rnPatAndThen mk (TuplePat pats boxed _)
; pats' <- rnLPatsAndThen mk pats
; return (TuplePat pats' boxed []) }
rnPatAndThen _ (SplicePat splice)
= do { -- XXX How to deal with free variables?
; (pat, _) <- liftCps $ rnSplicePat splice
; return pat }
rnPatAndThen mk (SplicePat splice)
= do { eith <- liftCpsFV $ rnSplicePat splice
; case eith of -- See Note [rnSplicePat] in RnSplice
Left not_yet_renamed -> rnPatAndThen mk not_yet_renamed
Right already_renamed -> return already_renamed }
rnPatAndThen mk (QuasiQuotePat qq)
= do { pat <- liftCps $ runQuasiQuotePat qq
-- Wrap the result of the quasi-quoter in parens so that we don't
......
......@@ -206,13 +206,40 @@ rnSpliceType splice k
}
; return (unLoc hs_ty3, fvs) }
----------------------
rnSplicePat :: HsSplice RdrName -> RnM (Pat Name, FreeVars)
\end{code}
Note [rnSplicePat]
~~~~~~~~~~~~~~~~~~
Renaming a pattern splice is a bit tricky, because we need the variables
bound in the pattern to be in scope in the RHS of the pattern. This scope
management is effectively done by using continuation-passing style in
RnPat, through the CpsRn monad. We don't wish to be in that monad here
(it would create import cycles and generally conflict with renaming other
splices), so we really want to return a (Pat RdrName) -- the result of
running the splice -- which can then be further renamed in RnPat, in
the CpsRn monad.
The problem is that if we're renaming a splice within a bracket, we
*don't* want to run the splice now. We really do just want to rename
it to an HsSplice Name. Of course, then we can't know what variables
are bound within the splice, so pattern splices within brackets aren't
all that useful.
In any case, when we're done in rnSplicePat, we'll either have a
Pat RdrName (the result of running a top-level splice) or a Pat Name
(the renamed nested splice). Thus, the awkward return type of
rnSplicePat.
\begin{code}
-- | Rename a splice pattern. See Note [rnSplicePat]
rnSplicePat :: HsSplice RdrName -> RnM ( Either (Pat RdrName) (Pat Name)
, FreeVars)
rnSplicePat splice
= rnSpliceGen False run_pat_splice pend_pat_splice splice
where
pend_pat_splice rn_splice@(HsSplice n e)
= (PendingRnPatSplice (PendSplice n e), SplicePat rn_splice)
= (PendingRnPatSplice (PendSplice n e), Right $ SplicePat rn_splice)
run_pat_splice (HsSplice _ expr')
= do { expr <- getHooked runRnSpliceHook return >>= ($ expr')
......@@ -227,10 +254,7 @@ rnSplicePat splice
; pat <- runMetaP zonked_q_expr
; showSplice "pattern" expr (ppr pat)
; (pat', fvs) <- checkNoErrs $
rnPat ThPatSplice pat $ \pat' -> return (pat', emptyFVs)
; return (unLoc pat', fvs) }
; return (Left $ unLoc pat, emptyFVs) }
----------------------
rnSpliceDecl :: SpliceDecl RdrName -> RnM (SpliceDecl Name, FreeVars)
......
......@@ -11,6 +11,7 @@ import Kind
rnSpliceType :: HsSplice RdrName -> PostTc Name Kind
-> RnM (HsType Name, FreeVars)
rnSplicePat :: HsSplice RdrName -> RnM (Pat Name, FreeVars)
rnSplicePat :: HsSplice RdrName -> RnM ( Either (Pat RdrName) (Pat Name)
, FreeVars )
rnSpliceDecl :: SpliceDecl RdrName -> RnM (SpliceDecl Name, FreeVars)
\end{code}
......@@ -344,5 +344,5 @@ test('T8100', normal, compile, ['-v0'])
test('T9064', normal, compile, ['-v0'])
test('T9209', normal, compile_fail, ['-v0'])
test('T7484', normal, compile_fail, ['-v0'])
test('T1476', expect_broken(1476), compile, ['-v0'])
test('T1476', normal, compile, ['-v0'])
test('T1476b', normal, compile_fail, ['-v0'])
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