Fix fast call type checker and add error message to pointer accessor …

…outside closure

checker/checker.go

@@ -327,8 +327,16 @@ func (v *visitor) FunctionNode(node *ast.FunctionNode) reflect.Type {
 	if f, ok := v.types[node.Name]; ok {
 		if fn, ok := isFuncType(f.Type); ok {
 
-			if !isInterface(fn) && fn.IsVariadic() && fn.NumOut() == 1 {
-				rest := fn.In(fn.NumIn() - 1)
+			inputParamsCount := 1 // for functions
+			if f.Method {
+				inputParamsCount = 2 // for methods
+			}
+
+			if !isInterface(fn) &&
+				fn.IsVariadic() &&
+				fn.NumIn() == inputParamsCount &&
+				fn.NumOut() == 1 {
+				rest := fn.In(fn.NumIn() - 1) // function has only one param for functions and two for methods
 				if rest.Kind() == reflect.Slice && rest.Elem().Kind() == reflect.Interface {
 					node.Fast = true
 				}
@@ -499,6 +507,10 @@ func (v *visitor) ClosureNode(node *ast.ClosureNode) reflect.Type {
 }
 
 func (v *visitor) PointerNode(node *ast.PointerNode) reflect.Type {
+	if len(v.collections) == 0 {
+		panic(v.error(node, "cannot use pointer accessor outside closure"))
+	}
+
 	collection := v.collections[len(v.collections)-1]
 
 	if t, ok := indexType(collection); ok {

expr_test.go

@@ -419,6 +419,24 @@ func TestOperator_interface(t *testing.T) {
 	require.Equal(t, true, output)
 }
 
+func TestExpr_readme_example(t *testing.T) {
+	env := map[string]interface{}{
+		"greet":   "Hello, %v!",
+		"names":   []string{"world", "you"},
+		"sprintf": fmt.Sprintf,
+	}
+
+	code := `sprintf(greet, names[0])`
+
+	program, err := expr.Compile(code, expr.Env(env))
+	require.NoError(t, err)
+
+	output, err := expr.Run(program, env)
+	require.NoError(t, err)
+
+	require.Equal(t, "Hello, world!", output)
+}
+
 func TestExpr(t *testing.T) {
 	env := &mockEnv{
 		Any:     "any",

parser/parser.go

@@ -77,6 +77,7 @@ type parser struct {
 	current Token
 	pos     int
 	err     *file.Error
+	closure bool
 }
 
 type Tree struct {
@@ -217,12 +218,18 @@ func (p *parser) parsePrimary() Node {
 		return p.parsePostfixExpression(expr)
 	}
 
-	if token.Is(Operator, "#") || token.Is(Operator, ".") {
-		if token.Is(Operator, "#") {
-			p.next()
+	if p.closure {
+		if token.Is(Operator, "#") || token.Is(Operator, ".") {
+			if token.Is(Operator, "#") {
+				p.next()
+			}
+			node := &PointerNode{Base: Loc(token.Location)}
+			return p.parsePostfixExpression(node)
+		}
+	} else {
+		if token.Is(Operator, "#") || token.Is(Operator, ".") {
+			p.error("cannot use pointer accessor outside closure")
 		}
-		node := &PointerNode{Base: Loc(token.Location)}
-		return p.parsePostfixExpression(node)
 	}
 
 	return p.parsePrimaryExpression()
@@ -353,7 +360,9 @@ func (p *parser) parseClosure() Node {
 	token := p.current
 	p.expect(Bracket, "{")
 
+	p.closure = true
 	node := p.parseExpression(0)
+	p.closure = false
 
 	p.expect(Bracket, "}")
 	return &ClosureNode{

parser/parser_test.go

@@ -265,6 +265,11 @@ foo({.bar})
 a map key must be a quoted string, a number, a identifier, or an expression enclosed in parentheses (unexpected token Operator(".")) (1:6)
  | foo({.bar})
  | .....^
+
+.foo
+cannot use pointer accessor outside closure (1:1)
+ | .foo
+ | ^
 `
 
 func TestParse_error(t *testing.T) {