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Add atom_length/2

--- a/builtins.c

+++ b/builtins.c

@@ -54,6 +54,7 @@

 BuiltinProto(builtinassertz);

 BuiltinProto(builtinretractone);

 BuiltinProto(builtinabolish);

+BuiltinProto(builtinatomlength);

 int compareterms(Term *, Term *);

@@ -151,6 +152,8 @@

 		return builtinretractone;

 	if(Match(L"abolish", 1))

 		return builtinabolish;

+	if(Match(L"atom_length", 2))

+		return builtinatomlength;

 	return nil;

 }

@@ -1107,4 +1110,25 @@

 		}

 	}

 	return 1;

+}

+

+int

+builtinatomlength(Term *goal, Binding **bindings, Module *module)

+{

+	USED(module);

+	Term *atom = goal->children;

+	Term *length = atom->next;

+	

+	if(atom->tag == VariableTerm)

+		Throw(instantiationerror());

+	if(atom->tag != AtomTerm)

+		Throw(typeerror(L"atom", atom));

+	if(length->tag != VariableTerm && length->tag != IntegerTerm)

+		Throw(typeerror(L"integer", length));

+	if(length->tag == IntegerTerm && length->ival < 0)

+		Throw(domainerror(L"not_less_than_zero", length));

+

+	int len = runestrlen(atom->text);

+	Term *reallength = mkinteger(len);

+	return unify(length, reallength, bindings);

 }

\ No newline at end of file