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| author | Richard Eisenberg <rae@richarde.dev> | 2019-09-25 12:28:40 +0100 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2019-10-03 12:17:30 -0400 |
| commit | 6655ec734a51eda91273585d8d8e3d5d308a6628 (patch) | |
| tree | 1f23c2d5e338b214add96b32899f303a7fcf3fc7 /compiler/parser | |
| parent | 67bf734c6c118aa7caa06875f253defe8b7dd271 (diff) | |
| download | haskell-6655ec734a51eda91273585d8d8e3d5d308a6628.tar.gz | |
Improve documentation around empty tuples/lists
This patch also changes the way we handle empty lists, simplifying
them somewhat. See Note [Empty lists]. Previously, we had to
special-case empty lists in the type-checker. Now no more!
Finally, this patch improves some documentation around the ir_inst
field used in the type-checker.
This breaks a test case, but I really think the problem is #17251,
not really related to this patch.
Test case: typecheck/should_compile/T13680
Diffstat (limited to 'compiler/parser')
| -rw-r--r-- | compiler/parser/Parser.y | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/compiler/parser/Parser.y b/compiler/parser/Parser.y index 21737b46e6..997f497510 100644 --- a/compiler/parser/Parser.y +++ b/compiler/parser/Parser.y @@ -259,6 +259,8 @@ from the Haskell98 data constructor for a tuple. Shift resolves in favor of sysdcon, which is good because a tuple section will get rejected if -XTupleSections is not specified. +See also Note [ExplicitTuple] in GHC.Hs.Expr. + ------------------------------------------------------------------------------- state 408 contains 1 shift/reduce conflicts. @@ -2934,6 +2936,9 @@ texp :: { ECP } amms (mkHsViewPatPV (comb2 $1 $>) $1 $3) [mu AnnRarrow $2] } -- Always at least one comma or bar. +-- Though this can parse just commas (without any expressions), it won't +-- in practice, because (,,,) is parsed as a name. See Note [ExplicitTuple] +-- in GHC.Hs.Expr. tup_exprs :: { forall b. DisambECP b => PV ([AddAnn],SumOrTuple b) } : texp commas_tup_tail { runECP_PV $1 >>= \ $1 -> @@ -2978,6 +2983,7 @@ tup_tail :: { forall b. DisambECP b => PV [Located (Maybe (Located b))] } -- The rules below are little bit contorted to keep lexps left-recursive while -- avoiding another shift/reduce-conflict. +-- Never empty. list :: { forall b. DisambECP b => SrcSpan -> PV (Located b) } : texp { \loc -> runECP_PV $1 >>= \ $1 -> mkHsExplicitListPV loc [$1] } @@ -3399,6 +3405,7 @@ con_list : con { sL1 $1 [$1] } | con ',' con_list {% addAnnotation (gl $1) AnnComma (gl $2) >> return (sLL $1 $> ($1 : unLoc $3)) } +-- See Note [ExplicitTuple] in GHC.Hs.Expr sysdcon_nolist :: { Located DataCon } -- Wired in data constructors : '(' ')' {% ams (sLL $1 $> unitDataCon) [mop $1,mcp $2] } | '(' commas ')' {% ams (sLL $1 $> $ tupleDataCon Boxed (snd $2 + 1)) @@ -3407,6 +3414,7 @@ sysdcon_nolist :: { Located DataCon } -- Wired in data constructors | '(#' commas '#)' {% ams (sLL $1 $> $ tupleDataCon Unboxed (snd $2 + 1)) (mo $1:mc $3:(mcommas (fst $2))) } +-- See Note [Empty lists] in GHC.Hs.Expr sysdcon :: { Located DataCon } : sysdcon_nolist { $1 } | '[' ']' {% ams (sLL $1 $> nilDataCon) [mos $1,mcs $2] } |