config/lang: add modulo

config/lang/ast/arithmetic_op.go

@@ -9,4 +9,5 @@ const (
 	ArithmeticOpSub
 	ArithmeticOpMul
 	ArithmeticOpDiv
+	ArithmeticOpMod
 )

config/lang/builtins.go

@@ -77,6 +77,8 @@ func builtinIntMath() ast.Function {
 					result *= arg
 				case ast.ArithmeticOpDiv:
 					result /= arg
+				case ast.ArithmeticOpMod:
+					result = result % arg
 				}
 			}
 

config/lang/check_types.go

@@ -131,6 +131,11 @@ func (tc *typeCheckArithmetic) TypeCheck(v *TypeCheck) (ast.Node, error) {
 		}
 	}
 
+	// Modulo doesn't work for floats
+	if mathType == ast.TypeFloat && tc.n.Op == ast.ArithmeticOpMod {
+		return nil, fmt.Errorf("modulo cannot be used with floats")
+	}
+
 	// Return type
 	v.StackPush(mathType)
 

config/lang/eval_test.go

@@ -71,6 +71,14 @@ func TestEval(t *testing.T) {
 			ast.TypeString,
 		},
 
+		{
+			"foo ${42%4}",
+			nil,
+			false,
+			"foo 2",
+			ast.TypeString,
+		},
+
 		{
 			"foo ${42.0+1.0}",
 			nil,

config/lang/lex.go

@@ -180,6 +180,9 @@ func (x *parserLex) lexModeInterpolation(yylval *parserSymType) int {
 		case '/':
 			yylval.token = &parserToken{Value: ast.ArithmeticOpDiv}
 			return ARITH_OP
+		case '%':
+			yylval.token = &parserToken{Value: ast.ArithmeticOpMod}
+			return ARITH_OP
 		default:
 			x.backup()
 			return x.lexId(yylval)