Adding break and continue for for loops. (#197)

* Add break and continue

* tweak the example for brievety

ast/ast.go

@@ -139,6 +139,11 @@ func (b Base) PrettyPrint(ps *PrintState) *PrintState {
 	return ps.Print(b.Literal())
 }
 
+// Break or continue statement.
+type ControlExpression struct {
+	Base
+}
+
 type ReturnStatement struct {
 	Base
 	ReturnValue Node

eval/eval.go

@@ -220,12 +220,14 @@ func (s *State) evalInternal(node any) object.Object { //nolint:funlen,gocyclo,g
 	case *ast.StringLiteral:
 		return object.String{Value: node.Literal()}
 
+	case *ast.ControlExpression:
+		return object.ReturnValue{Value: object.NULL, ControlType: node.Type()}
 	case *ast.ReturnStatement:
 		if node.ReturnValue == nil {
-			return object.ReturnValue{Value: object.NULL}
+			return object.ReturnValue{Value: object.NULL, ControlType: token.RETURN}
 		}
 		val := s.evalInternal(node.ReturnValue)
-		return object.ReturnValue{Value: val}
+		return object.ReturnValue{Value: val, ControlType: token.RETURN}
 	case *ast.Builtin:
 		return s.evalBuiltin(node)
 	case *ast.FunctionLiteral:
@@ -694,9 +696,24 @@ func (s *State) evalForInteger(fe *ast.ForExpression, start *object.Integer, end
 		if name != "" {
 			s.env.Set(name, object.Integer{Value: int64(i)})
 		}
-		lastEval = s.evalInternal(fe.Body)
-		if rt := lastEval.Type(); rt == object.RETURN || rt == object.ERROR {
-			return lastEval
+		nextEval := s.evalInternal(fe.Body)
+		switch nextEval.Type() {
+		case object.ERROR:
+			return nextEval
+		case object.RETURN:
+			r := nextEval.(object.ReturnValue)
+			switch r.ControlType {
+			case token.BREAK:
+				return lastEval
+			case token.CONTINUE:
+				continue
+			case token.RETURN:
+				return r
+			default:
+				return s.Errorf("for loop unexpected control type %s", r.ControlType.String())
+			}
+		default:
+			lastEval = nextEval
 		}
 	}
 	return lastEval
@@ -750,9 +767,25 @@ func (s *State) evalForList(fe *ast.ForExpression, list object.Object, name stri
 			return s.NewError("for list element is nil")
 		}
 		s.env.Set(name, v)
-		lastEval = s.evalInternal(fe.Body)
-		if rt := lastEval.Type(); rt == object.RETURN || rt == object.ERROR {
-			return lastEval
+		// Copy pasta from evalForInteger. hard to share control flow.
+		nextEval := s.evalInternal(fe.Body)
+		switch nextEval.Type() {
+		case object.ERROR:
+			return nextEval
+		case object.RETURN:
+			r := nextEval.(object.ReturnValue)
+			switch r.ControlType {
+			case token.BREAK:
+				return lastEval
+			case token.CONTINUE:
+				continue
+			case token.RETURN:
+				return r
+			default:
+				return s.Errorf("for loop unexpected control type %s", r.ControlType.String())
+			}
+		default:
+			lastEval = nextEval
 		}
 	}
 	return lastEval

eval/eval_api.go

@@ -9,6 +9,7 @@ import (
 	"grol.io/grol/lexer"
 	"grol.io/grol/object"
 	"grol.io/grol/parser"
+	"grol.io/grol/token"
 	"grol.io/grol/trie"
 )
 
@@ -18,7 +19,7 @@ import (
 // runtime: goroutine stack exceeds 1000000000-byte limit
 // fatal error: stack overflow. Was 250k but adding a log
 // in Error() makes it go over that (somehow).
-const DefaultMaxDepth = 195_000
+const DefaultMaxDepth = 150_000
 
 type State struct {
 	Out        io.Writer
@@ -114,6 +115,9 @@ func (s *State) Eval(node any) object.Object {
 	s.depth--
 	// unwrap return values only at the top.
 	if returnValue, ok := result.(object.ReturnValue); ok {
+		if returnValue.ControlType != token.RETURN {
+			return s.Errorf("unexpected control type %v outside of for loops", returnValue.ControlType)
+		}
 		return returnValue.Value
 	}
 	return result

examples/for.gr

@@ -14,13 +14,14 @@
 
 for 3 {println("this will be printed 3 times")}
 
-for i = -2:5 {println("i is",i)}
+// Also demonstrates break, loop ends when i > 3 instead of continuing to 36
+for i = -2:37 {println("i is",i); if i >= 3 {break}}
 
 // like first() iterating over maps produces key-value pairs (maps with keys `key` and `value`)
 for kv = {"c":3,"a":1,"b":2} {println("key",kv.key,"value",kv.value)}
 
 // iterating over arrays
 for v = [2,-5,7] {println("v",v)}
 
-// For strings iterations is on runes
-for c = "ab😀" {println("rune",c)}
+// For strings iterations is on runes - demonstrate continue (skip the "b")
+for c = "ab😀" {if c=="b" {continue} println("rune",c)}

examples/pi2.gr

@@ -9,5 +9,5 @@ f = func(i, n, prod) {
 	}
 	self(i+1, n, prod*(1-1./(2*i)))
 }
-n = 194_990 // close to 195_000 default limit.
+n = 149_990 // close to 150_000 default limit.
 f(1, n, 1)

object/object.go

@@ -507,7 +507,8 @@ func (e Error) Inspect() string {
 }
 
 type ReturnValue struct {
-	Value Object
+	Value       Object
+	ControlType token.Type
 }
 
 func (rv ReturnValue) JSON(w io.Writer) error {

parser/parser.go

@@ -75,6 +75,8 @@ func New(l *lexer.Lexer) *Parser {
 	p.registerPrefix(token.LPAREN, p.parseGroupedExpression)
 	p.registerPrefix(token.IF, p.parseIfExpression)
 	p.registerPrefix(token.FOR, p.parseForExpression)
+	p.registerPrefix(token.BREAK, p.parseControlExpression)
+	p.registerPrefix(token.CONTINUE, p.parseControlExpression)
 	p.registerPrefix(token.FUNC, p.parseFunctionLiteral)
 	p.registerPrefix(token.STRING, p.parseStringLiteral)
 	p.registerPrefix(token.LEN, p.parseBuiltin)
@@ -500,6 +502,12 @@ func (p *Parser) parseInfixExpression(left ast.Node) ast.Node {
 	return expression
 }
 
+func (p *Parser) parseControlExpression() ast.Node {
+	expression := &ast.ControlExpression{}
+	expression.Token = p.curToken
+	return expression
+}
+
 func (p *Parser) parseForExpression() ast.Node {
 	expression := &ast.ForExpression{}
 	expression.Token = p.curToken

token/token.go

@@ -128,6 +128,8 @@ const (
 	ELSE
 	RETURN
 	FOR
+	BREAK
+	CONTINUE
 	// Macro magic.
 	MACRO
 	QUOTE