parser: handle operator methods and fix them in vdoc

vlib/bignum/bignum.v

@@ -176,7 +176,7 @@ pub fn (a Number) clone() Number {
 	return b
 }
 ////////////////////////////////////////////////////////////
-pub fn factorial(nn bignum.Number) bignum.Number {
+pub fn factorial(nn Number) Number {
 	mut n := nn.clone()
 	mut a := nn.clone()
 	n.dec()
@@ -190,6 +190,6 @@ pub fn factorial(nn bignum.Number) bignum.Number {
 	return a
 }
 
-pub fn fact(n int) bignum.Number {
+pub fn fact(n int) Number {
 	return factorial( bignum.from_int(n) )
 }

vlib/v/gen/cgen.v

@@ -350,6 +350,9 @@ fn (g mut Gen) gen_fn_decl(it ast.FnDecl) {
 			name = g.table.get_type_symbol(it.receiver.typ).name + '_' + name
 		}
 		name = name.replace('.', '__')
+		if name.starts_with('_op_') {
+			name = op_to_fn_name(name)
+		}
 		// type_name := g.table.type_to_str(it.typ)
 		type_name := g.typ(it.typ)
 		g.write('$type_name ${name}(')
@@ -949,3 +952,25 @@ fn (g &Gen) sort_structs(types []table.TypeSymbol) []table.TypeSymbol {
 	}
 	return types_sorted
 }
+
+fn op_to_fn_name(name string) string {
+	return match name {
+		'+'{
+			'_op_plus'
+		}
+		'-'{
+			'_op_minus'
+		}
+		'*'{
+			'_op_mul'
+		}
+		'/'{
+			'_op_div'
+		}
+		'%'{
+			'_op_mod'
+		}
+		else {
+			'bad op $name'}
+	}
+}

vlib/v/parser/fn.v

@@ -99,6 +99,10 @@ fn (p mut Parser) fn_decl() ast.FnDecl {
 		// TODO high
 		name = p.check_name()
 	}
+	if p.tok.kind in [.plus, .minus, .mul, .div, .mod] {
+		name = p.tok.kind.str() // op_to_fn_name()
+		p.next()
+	}
 	// <T>
 	if p.tok.kind == .lt {
 		p.next()