Improve and test support for custom functions

* NamesLocalVariablesFunction actually is a kernel operation, mark it as such
* fix a crash caused by infinite recursion when trying to display a function
  which is not a `T_FUNCTION`
* add tests for installing custom methods for NameFunction,
  NamesLocalVariablesFunction, and NumberArgumentsFunction

lib/function.g

@@ -162,10 +162,10 @@ DeclareOperationKernel("NameFunction", [IS_OBJECT], NAME_FUNC);
 
 #############################################################################
 ##
-#F  SetNameFunction( <func>, <name> )  . . . . . . . .set  name of a function
+#O  SetNameFunction( <func>, <name> )  . . . . . . . .set  name of a function
 ##
 ##  <ManSection>
-##  <Func Name="SetNameFunction" Arg='func, name'/>
+##  <Oper Name="SetNameFunction" Arg='func, name'/>
 ##
 ##  <Description>
 ##  changes the name of a function. This only changes the name stored in
@@ -174,15 +174,12 @@ DeclareOperationKernel("NameFunction", [IS_OBJECT], NAME_FUNC);
 ##  </Description>
 ##  </ManSection>
 ##
-#T  If objects simulate functions this must become an operation, or an attribute
-#T  with the above
-##
 DeclareOperationKernel( "SetNameFunction", [IS_OBJECT, IS_STRING], SET_NAME_FUNC );
 
 
 #############################################################################
 ##
-#F  NumberArgumentsFunction( <func> )
+#O  NumberArgumentsFunction( <func> )
 ##
 ##  <#GAPDoc Label="NumberArgumentsFunction">
 ##  <ManSection>
@@ -216,7 +213,7 @@ DeclareOperationKernel( "NumberArgumentsFunction", [IS_OBJECT], NARG_FUNC );
 
 #############################################################################
 ##
-#F  NamesLocalVariablesFunction( <func> )
+#O  NamesLocalVariablesFunction( <func> )
 ##
 ##  <#GAPDoc Label="NamesLocalVariablesFunction">
 ##  <ManSection>
@@ -229,7 +226,7 @@ DeclareOperationKernel( "NumberArgumentsFunction", [IS_OBJECT], NARG_FUNC );
 ##  <A>func</A>, and the remaining ones are the local variables as given in
 ##  the <K>local</K> statement in <A>func</A>.
 ##  (The number of arguments can be computed with
-##  <Ref Func="NumberArgumentsFunction"/>.)
+##  <Ref Oper="NumberArgumentsFunction"/>.)
 ##  <P/>
 ##  <Example><![CDATA[
 ##  gap> NamesLocalVariablesFunction(function( a, b ) local c; return 1; end);
@@ -243,7 +240,7 @@ DeclareOperationKernel( "NumberArgumentsFunction", [IS_OBJECT], NARG_FUNC );
 ##  </ManSection>
 ##  <#/GAPDoc>
 ##
-BIND_GLOBAL( "NamesLocalVariablesFunction", NAMS_FUNC );
+DeclareOperationKernel( "NamesLocalVariablesFunction", [IS_OBJECT], NAMS_FUNC );
 
 
 #############################################################################
@@ -368,7 +365,7 @@ end);
 
 #############################################################################
 ##
-#F  CallFuncList( <func>, <args> )  . . . . . . . . . . . . . call a function
+#O  CallFuncList( <func>, <args> )  . . . . . . . . . . . . . call a function
 ##
 ##  <#GAPDoc Label="CallFuncList">
 ##  <ManSection>
@@ -389,7 +386,7 @@ end);
 ##  13
 ##  ]]></Example>
 ##  <P/>
-##  A more useful application of <Ref Func="CallFuncList"/> is for a function
+##  A more useful application of <Ref Oper="CallFuncList"/> is for a function
 ##  <C>g</C> that is called in the body of a function <C>f</C> with
 ##  (a sublist of) the arguments of <C>f</C>, where <C>f</C> has been defined
 ##  with a single formal argument <C>arg</C>
@@ -441,8 +438,6 @@ end);
 ##  </ManSection>
 ##  <#/GAPDoc>
 ##
-#T  If objects simulate functions this must become an operation.
-##
 UNBIND_GLOBAL("CallFuncList"); # was declared 2b defined
 DeclareOperationKernel( "CallFuncList", [IS_OBJECT, IS_LIST], CALL_FUNC_LIST );
 DeclareOperationKernel( "CallFuncListWrap", [IS_OBJECT, IS_LIST], CALL_FUNC_LIST_WRAP );

lib/function.gi

@@ -10,7 +10,7 @@
 ##  that they need to be in function.g
 ##
 
-InstallMethod( ViewString, "for a function", true, [IsFunction], 0,
+InstallMethod( ViewString, "for a function", [IsFunction and IsInternalRep],
 function(func)
     local  locks, nams, narg, i, isvarg, result;
     result := "";
@@ -60,7 +60,7 @@ function(func)
     return result;
 end);
 
-InstallMethod(DisplayString, "for a function, using string stream", [IsFunction],
+InstallMethod(DisplayString, "for a function, using string stream", [IsFunction and IsInternalRep],
 function(fun)
     local  s, stream;
     s := "";
@@ -71,7 +71,7 @@ function(fun)
     return MakeImmutable(s);
 end);
 
-InstallMethod(String, "for a function, with whitespace reduced", [IsFunction],
+InstallMethod(String, "for a function, with whitespace reduced", [IsFunction and IsInternalRep],
 function(fun)
     local  s, str;
     s := ShallowCopy(DisplayString(fun));

tst/testinstall/callfunc.tst

@@ -29,12 +29,25 @@ gap> ForAll([0..100], x -> CallFuncListWrap(swallow, List([1..x], y -> [y]) ) =
 true
 
 # test overloading CallFuncList
-gap> fam := NewFamily("XYZsFamily");;
-gap> cat := NewCategory("IsXYZ",IsObject);;
+gap> fam := NewFamily("CustomFunctionFamily");;
+gap> cat := NewCategory("IsCustomFunction", IsFunction);;
 gap> type := NewType(fam, cat and IsPositionalObjectRep);;
 gap> result := fail;;
 gap> InstallMethod(CallFuncList,[cat,IsList],function(func,args) result:=args; return args; end);
-gap> o := Objectify(type,[]);;
+gap> InstallMethod(NameFunction, [cat], f -> f![1]);
+gap> InstallMethod(NamesLocalVariablesFunction, [cat], f -> ["arg"]);
+gap> InstallMethod(NumberArgumentsFunction, [cat], f -> -1);
+
+#
+gap> o := Objectify(type,["myName"]);;
+gap> Display(o);
+<object>
+gap> NameFunction(o);
+"myName"
+gap> NamesLocalVariablesFunction(o);
+[ "arg" ]
+gap> NumberArgumentsFunction(o);
+-1
 
 # test dispatch through interpreter / IntrFuncCallEnd
 gap> o();
@@ -109,7 +122,7 @@ gap> CallFuncList(o, [1,2,3,4,5,6,7]);
 [ 1, 2, 3, 4, 5, 6, 7 ]
 
 # test overloading CallFuncList with a procedure call
-gap> cat2 := NewCategory("IsXYZ2",IsObject);;
+gap> cat2 := NewCategory("IsCustomFunction2",IsFunction);;
 gap> type2 := NewType(fam, cat2 and IsPositionalObjectRep);;
 gap> InstallMethod(CallFuncList,[cat2,IsList],function(func,args) result:=args; end);
 gap> o2 := Objectify(type2,[]);;