Parser: use 'error' token in error reporting rules

Summary:
It exempts us from 11 reduce/reduce conflicts and
12 shift/reduce conflicts.
Signed-off-by: Sergei Trofimovich <siarheit@google.com>

Reviewers: simonpj, mikeizbicki, austin, simonmar

Reviewed By: simonmar

Subscribers: carter, thomie

Differential Revision: https://phabricator.haskell.org/D571

compiler/parser/Parser.y

@@ -87,6 +87,12 @@ import TysWiredIn       ( unitTyCon, unitDataCon, tupleTyCon, tupleCon, nilDataC
 }
 
 {-
+-----------------------------------------------------------------------------
+14 Dec 2014
+
+Conflicts: 48 shift/reduce
+           1  reduce/reduce
+
 -----------------------------------------------------------------------------
 20 Nov 2014
 
@@ -1969,33 +1975,34 @@ exp10 :: { LHsExpr RdrName }
         | fexp                         { $1 }
 
         -- parsing error messages go below here
-        | '\\' apat apats opt_asig '->'              {% parseErrorSDoc (combineLocs $1 $5) $ text
+        | '\\' apat apats opt_asig '->' error        {% parseErrorSDoc (combineLocs $1 $5) $ text
                                                         "parse error in lambda: no expression after '->'"
                                                      }
-        | '\\'                                       {% parseErrorSDoc (getLoc $1) $ text
+        | '\\' error                                 {% parseErrorSDoc (getLoc $1) $ text
                                                         "parse error: naked lambda expression '\'"
                                                      }
-        | 'let' binds 'in'                           {% parseErrorSDoc (combineLocs $1 $2) $ text
+        | 'let' binds 'in' error                     {% parseErrorSDoc (combineLocs $1 $2) $ text
                                                         "parse error in let binding: missing expression after 'in'"
                                                      }
-        | 'let' binds                                {% parseErrorSDoc (combineLocs $1 $2) $ text
+        | 'let' binds error                          {% parseErrorSDoc (combineLocs $1 $2) $ text
                                                         "parse error in let binding: missing required 'in'"
                                                      }
-        | 'let'                                      {% parseErrorSDoc (getLoc $1) $ text
+        | 'let' error                                {% parseErrorSDoc (getLoc $1) $ text
                                                         "parse error: naked let binding"
                                                      }
-        | 'if' exp optSemi 'then' exp optSemi 'else' {% hintIf (combineLocs $1 $5) "else clause empty" }
-        | 'if' exp optSemi 'then' exp optSemi        {% hintIf (combineLocs $1 $5) "missing required else clause" }
-        | 'if' exp optSemi 'then'                    {% hintIf (combineLocs $1 $2) "then clause empty" }
-        | 'if' exp optSemi                           {% hintIf (combineLocs $1 $2) "missing required then and else clauses" }
-        | 'if'                                       {% hintIf (getLoc $1) "naked if statement" }
-        | 'case' exp 'of'                            {% parseErrorSDoc (combineLocs $1 $2) $ text
+        | 'if' exp optSemi 'then' exp optSemi
+          'else' error                               {% hintIf (combineLocs $1 $5) "else clause empty" }
+        | 'if' exp optSemi 'then' exp optSemi error  {% hintIf (combineLocs $1 $5) "missing required else clause" }
+        | 'if' exp optSemi 'then' error              {% hintIf (combineLocs $1 $2) "then clause empty" }
+        | 'if' exp optSemi error                     {% hintIf (combineLocs $1 $2) "missing required then and else clauses" }
+        | 'if' error                                 {% hintIf (getLoc $1) "naked if statement" }
+        | 'case' exp 'of' error                      {% parseErrorSDoc (combineLocs $1 $2) $ text
                                                         "parse error in case statement: missing list after '->'"
                                                      }
-        | 'case' exp                                 {% parseErrorSDoc (combineLocs $1 $2) $ text
+        | 'case' exp error                           {% parseErrorSDoc (combineLocs $1 $2) $ text
                                                         "parse error in case statement: missing required 'of'"
                                                      }
-        | 'case'                                     {% parseErrorSDoc (getLoc $1) $ text
+        | 'case' error                               {% parseErrorSDoc (getLoc $1) $ text
                                                         "parse error: naked case statement"
                                                      }
 optSemi :: { ([Located a],Bool) }