From cda79cfc847a84c3cac158684530c8aabc462814 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Mon, 30 Apr 2018 21:59:01 +0200
Subject: [PATCH] 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               |  2 +-
 lib/function.gi              |  3 +++
 tst/testinstall/callfunc.tst | 16 ++++++++++++----
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/lib/function.g b/lib/function.g
index fde53d9fb7..7604174d0d 100644
--- a/lib/function.g
+++ b/lib/function.g
@@ -243,7 +243,7 @@ DeclareOperationKernel( "NumberArgumentsFunction", [IS_OBJECT], NARG_FUNC );
 ##  </ManSection>
 ##  <#/GAPDoc>
 ##
-BIND_GLOBAL( "NamesLocalVariablesFunction", NAMS_FUNC );
+DeclareOperationKernel( "NamesLocalVariablesFunction", [IS_OBJECT], NAMS_FUNC );
 
 
 #############################################################################
diff --git a/lib/function.gi b/lib/function.gi
index d587e68c06..bb02952abd 100644
--- a/lib/function.gi
+++ b/lib/function.gi
@@ -63,6 +63,9 @@ end);
 InstallMethod(DisplayString, "for a function, using string stream", [IsFunction],
 function(fun)
     local  s, stream;
+    if TNUM_OBJ(fun) <> T_FUNCTION then
+      TryNextMethod();
+    fi;
     s := "";
     stream := OutputTextString(s, true);
     PrintTo(stream, fun);
diff --git a/tst/testinstall/callfunc.tst b/tst/testinstall/callfunc.tst
index b833333578..0345f1b5cf 100644
--- a/tst/testinstall/callfunc.tst
+++ b/tst/testinstall/callfunc.tst
@@ -29,12 +29,20 @@ 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"]);
+function( arg... ) ... end
+gap> Display(o);
+<object>
 
 # test dispatch through interpreter / IntrFuncCallEnd
 gap> o();
@@ -109,7 +117,7 @@ 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,[]);;