[project @ 2001-10-25 02:13:10 by sof]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcClassDcl.lhs

diff --git a/ghc/compiler/typecheck/TcClassDcl.lhs b/ghc/compiler/typecheck/TcClassDcl.lhs
index 90b17fd..82d5ebb 100644 (file)
--- a/ghc/compiler/typecheck/TcClassDcl.lhs
+++ b/ghc/compiler/typecheck/TcClassDcl.lhs
@@ -53,7 +53,7 @@ import Var            ( TyVar )
 import VarSet          ( mkVarSet, emptyVarSet )
 import CmdLineOpts
 import ErrUtils                ( dumpIfSet )
-import Util            ( count )
+import Util            ( count, isSingleton, lengthIs, equalLength )
 import Maybes          ( seqMaybe, maybeToBool )
 \end{code}
 
@@ -122,7 +122,7 @@ tcClassDecl1 rec_env
        -- The renamer has already checked that the context mentions
        -- only the type variable of the class decl.
        -- Context is already kind-checked
-    ASSERT( length context == length sc_sel_names )
+    ASSERT( equalLength context sc_sel_names )
     tcHsTheta context                                          `thenTc` \ sc_theta ->
 
        -- CHECK THE CLASS SIGNATURES,
@@ -193,7 +193,7 @@ checkDefaultBinds clas ops (Just mbs)
       where
        n_generic    = count (maybeToBool . maybeGenericMatch) matches
        none_generic = n_generic == 0
-       all_generic  = n_generic == length matches
+       all_generic  = matches `lengthIs` n_generic
 \end{code}
 
 
@@ -262,7 +262,7 @@ checkValidClass cls
     doptsTc Opt_GlasgowExts                            `thenTc` \ gla_exts ->
 
        -- Check that the class is unary, unless GlaExs
-    checkTc (arity > 0)                (nullaryClassErr cls)   `thenTc_`
+    checkTc (not (null tyvars))                (nullaryClassErr cls)   `thenTc_`
     checkTc (gla_exts || unary) (classArityErr cls)    `thenTc_`
 
        -- Check the super-classes
@@ -278,8 +278,7 @@ checkValidClass cls
 
   where
     (tyvars, theta, _, op_stuff) = classBigSig cls
-    arity      = length tyvars
-    unary      = arity == 1
+    unary      = isSingleton tyvars
     no_generics = null [() | (_, GenDefMeth) <- op_stuff]
 
     check_op (sel_id, dm)