Don't print parens around list comprehensions

[ghc-hetmet.git] / compiler / hsSyn / HsExpr.lhs

diff --git a/compiler/hsSyn/HsExpr.lhs b/compiler/hsSyn/HsExpr.lhs
index a5f5f30..44d9b43 100644 (file)
--- a/compiler/hsSyn/HsExpr.lhs
+++ b/compiler/hsSyn/HsExpr.lhs
@@ -285,8 +285,18 @@ pprLExpr :: OutputableBndr id => LHsExpr id -> SDoc
 pprLExpr (L _ e) = pprExpr e
 
 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
-pprExpr e | isAtomicHsExpr e = ppr_expr e      -- Never replace 'x' by "..."
-         | otherwise        = pprDeeper (ppr_expr e)
+pprExpr e | isAtomicHsExpr e || isQuietHsExpr e =            ppr_expr e
+          | otherwise                           = pprDeeper (ppr_expr e)
+
+isQuietHsExpr :: HsExpr id -> Bool
+-- Parentheses do display something, but it gives little info and
+-- if we go deeper when we go inside them then we get ugly things
+-- like (...)
+isQuietHsExpr (HsPar _) = True
+-- applications don't display anything themselves
+isQuietHsExpr (HsApp _ _) = True
+isQuietHsExpr (OpApp _ _ _ _) = True
+isQuietHsExpr _ = False
 
 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
 pprBinds b = pprDeeper (ppr b)
@@ -473,17 +483,19 @@ pprParendExpr expr
        -- I think that is usually (always?) right
     in
     case unLoc expr of
-      HsLit l          -> pp_as_was
-      HsOverLit l      -> pp_as_was
-      HsVar _          -> pp_as_was
-      HsIPVar _                -> pp_as_was
-      ExplicitList _ _  -> pp_as_was
-      ExplicitPArr _ _  -> pp_as_was
-      ExplicitTuple _ _        -> pp_as_was
-      HsPar _          -> pp_as_was
-      HsBracket _      -> pp_as_was
-      HsBracketOut _ []        -> pp_as_was
-      _                        -> parens pp_as_was
+      HsLit l             -> pp_as_was
+      HsOverLit l         -> pp_as_was
+      HsVar _             -> pp_as_was
+      HsIPVar _                   -> pp_as_was
+      ExplicitList _ _     -> pp_as_was
+      ExplicitPArr _ _     -> pp_as_was
+      ExplicitTuple _ _           -> pp_as_was
+      HsPar _             -> pp_as_was
+      HsBracket _         -> pp_as_was
+      HsBracketOut _ []           -> pp_as_was
+      HsDo sc _ _ _
+       | isListCompExpr sc -> pp_as_was
+      _                           -> parens pp_as_was
 
 isAtomicHsExpr :: HsExpr id -> Bool    -- A single token
 isAtomicHsExpr (HsVar {})     = True
@@ -684,11 +696,9 @@ pprMatch ctxt (Match pats maybe_ty grhss)
 
 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
 pprGRHSs ctxt (GRHSs grhss binds)
-  = pprDeeper
-    (vcat (map (pprGRHS ctxt . unLoc) grhss)
-      $$
-     if isEmptyLocalBinds binds then empty
-     else text "where" $$ nest 4 (pprBinds binds))
+  = vcat (map (pprGRHS ctxt . unLoc) grhss)
+ $$ if isEmptyLocalBinds binds then empty
+                               else text "where" $$ nest 4 (pprBinds binds)
 
 pprGRHS :: OutputableBndr id => HsMatchContext id -> GRHS id -> SDoc
 
@@ -928,7 +938,12 @@ data HsStmtContext id
 isDoExpr :: HsStmtContext id -> Bool
 isDoExpr DoExpr      = True
 isDoExpr (MDoExpr _) = True
-isDoExpr other       = False
+isDoExpr _           = False
+
+isListCompExpr :: HsStmtContext id -> Bool
+isListCompExpr ListComp = True
+isListCompExpr PArrComp = True
+isListCompExpr _        = False
 \end{code}
 
 \begin{code}