import BasicTypes
import DataCon
import SrcLoc
+import Util( dropTail )
import Outputable
import FastString
-- because in this context we never use
-- the PatGuard or ParStmt variant
[LStmt id] -- "do":one or more stmts
- (LHsExpr id) -- The body; the last expression in the
- -- 'do' of [ body | ... ] in a list comp
- (SyntaxExpr id) -- The 'return' function, see Note
- -- [Monad Comprehensions]
PostTcType -- Type of the whole expression
| ExplicitList -- syntactic list
= sep [hang (ptext (sLit "let")) 2 (pprBinds binds),
hang (ptext (sLit "in")) 2 (ppr expr)]
-ppr_expr (HsDo do_or_list_comp stmts body _ _) = pprDo do_or_list_comp stmts body
+ppr_expr (HsDo do_or_list_comp stmts _) = pprDo do_or_list_comp stmts
ppr_expr (ExplicitList _ exprs)
= brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
HsPar {} -> pp_as_was
HsBracket {} -> pp_as_was
HsBracketOut _ [] -> pp_as_was
- HsDo sc _ _ _ _
+ HsDo sc _ _
| isListCompExpr sc -> pp_as_was
_ -> parens pp_as_was
-- The SyntaxExprs in here are used *only* for do-notation and monad
-- comprehensions, which have rebindable syntax. Otherwise they are unused.
data StmtLR idL idR
- = BindStmt (LPat idL)
+ = LastStmt -- Always the last Stmt in ListComp, MonadComp, PArrComp, DoExpr, MDoExpr
+ -- Not used for GhciStmt, PatGuard, which scope over other stuff
+ (LHsExpr idR)
+ (SyntaxExpr idR) -- The return operator, used only for MonadComp
+ -- See Note [Monad Comprehensions]
+ | BindStmt (LPat idL)
(LHsExpr idR)
(SyntaxExpr idR) -- The (>>=) operator
(SyntaxExpr idR) -- The fail operator
-- ParStmts only occur in a list/monad comprehension
| ParStmt [([LStmt idL], [idR])]
- (SyntaxExpr idR) -- polymorphic `mzip` for monad comprehensions
+ (SyntaxExpr idR) -- Polymorphic `mzip` for monad comprehensions
(SyntaxExpr idR) -- The `>>=` operator
- (SyntaxExpr idR) -- polymorphic `return` operator
+ (SyntaxExpr idR) -- Polymorphic `return` operator
+ -- with type (forall a. a -> m a)
-- See notes [Monad Comprehensions]
-- After renaming, the ids are the binders bound by the stmts and used
-- because the Id may be *polymorphic*, but
-- the returned thing has to be *monomorphic*,
-- so they may be type applications
+
+ , recS_ret_ty :: PostTcType -- The type of of do { stmts; return (a,b,c) }
+ -- With rebindable syntax the type might not
+ -- be quite as simple as (m (tya, tyb, tyc)).
}
deriving (Data, Typeable)
\end{code}
Note [Monad Comprehensions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Monad comprehensions require seperate functions like 'return' and '>>=' for
-desugaring. These functions are stored in the 'HsDo' expression and the
-statements used in monad comprehensions. For example, the 'return' of the
-'HsDo' expression is used to lift the body of the monad comprehension:
+Monad comprehensions require separate functions like 'return' and
+'>>=' for desugaring. These functions are stored in the statements
+used in monad comprehensions. For example, the 'return' of the 'LastStmt'
+expression is used to lift the body of the monad comprehension:
[ body | stmts ]
=>
ppr stmt = pprStmt stmt
pprStmt :: (OutputableBndr idL, OutputableBndr idR) => (StmtLR idL idR) -> SDoc
+pprStmt (LastStmt expr _) = ppr expr
pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext (sLit "<-"), ppr expr]
pprStmt (LetStmt binds) = hsep [ptext (sLit "let"), pprBinds binds]
pprStmt (ExprStmt expr _ _ _) = ppr expr
pprBy Nothing = empty
pprBy (Just e) = ptext (sLit "by") <+> ppr e
-pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
-pprDo DoExpr stmts body = ptext (sLit "do") <+> ppr_do_stmts stmts body
-pprDo GhciStmt stmts body = ptext (sLit "do") <+> ppr_do_stmts stmts body
-pprDo MDoExpr stmts body = ptext (sLit "mdo") <+> ppr_do_stmts stmts body
-pprDo ListComp stmts body = brackets $ pprComp stmts body
-pprDo PArrComp stmts body = pa_brackets $ pprComp stmts body
-pprDo MonadComp stmts body = brackets $ pprComp stmts body
-pprDo _ _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
+pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> SDoc
+pprDo DoExpr stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
+pprDo GhciStmt stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
+pprDo MDoExpr stmts = ptext (sLit "mdo") <+> ppr_do_stmts stmts
+pprDo ListComp stmts = brackets $ pprComp stmts
+pprDo PArrComp stmts = pa_brackets $ pprComp stmts
+pprDo MonadComp stmts = brackets $ pprComp stmts
+pprDo _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
-ppr_do_stmts :: OutputableBndr id => [LStmt id] -> LHsExpr id -> SDoc
+ppr_do_stmts :: OutputableBndr id => [LStmt id] -> SDoc
-- Print a bunch of do stmts, with explicit braces and semicolons,
-- so that we are not vulnerable to layout bugs
-ppr_do_stmts stmts body
- = lbrace <+> pprDeeperList vcat ([ppr s <> semi | s <- stmts] ++ [ppr body])
+ppr_do_stmts stmts
+ = lbrace <+> pprDeeperList vcat ([ppr s <> semi | s <- stmts])
<+> rbrace
ppr_lc_stmts :: OutputableBndr id => [LStmt id] -> [SDoc]
ppr_lc_stmts stmts = [ppr s <> comma | s <- stmts]
-pprComp :: OutputableBndr id => [LStmt id] -> LHsExpr id -> SDoc
-pprComp quals body -- Prints: body | qual1, ..., qualn
- = hang (ppr body <+> char '|') 2 (interpp'SP quals)
+pprComp :: OutputableBndr id => [LStmt id] -> SDoc
+pprComp quals -- Prints: body | qual1, ..., qualn
+ | not (null quals)
+ , L _ (LastStmt body _) <- last quals
+ = hang (ppr body <+> char '|') 2 (interpp'SP (dropTail 1 quals))
+ | otherwise
+ = pprPanic "pprComp" (interpp'SP quals)
\end{code}
%************************************************************************
data HsStmtContext id
= ListComp
- | DoExpr
- | GhciStmt -- A command-line Stmt in GHCi pat <- rhs
- | MDoExpr -- Recursive do-expression
| MonadComp
| PArrComp -- Parallel array comprehension
+
+ | DoExpr -- do { ... }
+ | MDoExpr -- mdo { ... } ie recursive do-expression
+
+ | GhciStmt -- A command-line Stmt in GHCi pat <- rhs
| PatGuard (HsMatchContext id) -- Pattern guard for specified thing
| ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
| TransformStmtCtxt (HsStmtContext id) -- A branch of a transform stmt
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