eval: add len

README.md

@@ -9,9 +9,8 @@
 - Destructuring assignment
 - `maptable`
 - `coerce`
-- `len`
 - `mac`
-- `\``
+- `````
 - `w/link`
 - `aform`
 - ...

eval/eval.go

@@ -26,6 +26,7 @@ func RootEnv() ast.Env {
 		"pr":    evalPr,
 		"table": evalTable,
 		"type":  evalType,
+		"len":   evalLen,
 	}
 
 	for k, v := range prims {
@@ -453,6 +454,33 @@ func evalType(l []*ast.AST) (*ast.AST, error) {
 	return l[0].Type(), nil
 }
 
+func evalLen(l []*ast.AST) (*ast.AST, error) {
+	err := checkArity(l, 1, "len")
+
+	if err != nil {
+		return nil, err
+	}
+
+	cnt := 0
+	elem := l[0]
+
+	switch elem.Tag {
+	case ast.Quoted:
+		// TODO: error handling
+		cnt = len(elem.Val.(*ast.AST).Val.([]*ast.AST))
+	case ast.String:
+		cnt = len(elem.Val.(string))
+	case ast.Table:
+		cnt = len(elem.Val.(map[*ast.AST]*ast.AST))
+	default:
+		return nil, fmt.Errorf("Cannot get length of %s", elem.Pretty())
+	}
+
+	res := ast.AST{ast.Num, float64(cnt)}
+
+	return &res, nil
+}
+
 func evalSymbolList(l []*ast.AST, e ast.Env) (*ast.AST, error) {
 	sym := l[0].Val.(string)