Use do-notation

diff --git a/compiler/rename/RnSource.lhs b/compiler/rename/RnSource.lhs
index c86b626..27de40f 100644 (file)
--- a/compiler/rename/RnSource.lhs
+++ b/compiler/rename/RnSource.lhs
@@ -500,17 +500,18 @@ rnSrcDerivDecl (DerivDecl ty)
 rnHsRuleDecl :: RuleDecl RdrName -> RnM (RuleDecl Name, FreeVars)
 rnHsRuleDecl (HsRule rule_name act vars lhs _fv_lhs rhs _fv_rhs)
   = bindPatSigTyVarsFV (collectRuleBndrSigTys vars)    $
-
     bindLocatedLocalsFV doc (map get_var vars)         $ \ ids ->
-    mapFvRn rn_var (vars `zip` ids)            `thenM` \ (vars', fv_vars) ->
+    do { (vars', fv_vars) <- mapFvRn rn_var (vars `zip` ids)
+               -- NB: The binders in a rule are always Ids
+               --     We don't (yet) support type variables
 
-    rnLExpr lhs                                        `thenM` \ (lhs', fv_lhs') ->
-    rnLExpr rhs                                        `thenM` \ (rhs', fv_rhs') ->
+       ; (lhs', fv_lhs') <- rnLExpr lhs
+       ; (rhs', fv_rhs') <- rnLExpr rhs
 
-    checkValidRule rule_name ids lhs' fv_lhs'  `thenM_`
+       ; checkValidRule rule_name ids lhs' fv_lhs'
 
-    returnM (HsRule rule_name act vars' lhs' fv_lhs' rhs' fv_rhs',
-            fv_vars `plusFV` fv_lhs' `plusFV` fv_rhs')
+       ; return (HsRule rule_name act vars' lhs' fv_lhs' rhs' fv_rhs',
+                 fv_vars `plusFV` fv_lhs' `plusFV` fv_rhs') }
   where
     doc = text "In the transformation rule" <+> ftext rule_name