for loop

interpreter.go

@@ -231,7 +231,6 @@ func (i *Interpreter) visitWhileStmt(w *WhileStmt) {
 		}
 
 		w.body.accept(i)
-
 	}
 }
 

parser.go

@@ -69,6 +69,7 @@ func (p *Parser) varDecl() Stmt {
 // statement ->  exprStmt
 //
 //	| whileStmt
+//	| forStmt
 //	| printStmt
 //	| blockStmt
 //	| breakStmt
@@ -95,6 +96,10 @@ func (p *Parser) statement() Stmt {
 		return p.whileStmt()
 	}
 
+	if p.match(FOR) {
+		return p.forStmt()
+	}
+
 	if p.match(BREAK) {
 		return p.breakStmt()
 	}
@@ -171,6 +176,60 @@ func (p *Parser) whileStmt() Stmt {
 	return &WhileStmt{cond, body}
 }
 
+// for -> "for" ( "(" ( varDecl | exprStmt | ";" ) expression? ";" expression  ")" )? statement
+func (p *Parser) forStmt() Stmt {
+
+	if p.check(LEFT_BRACE) {
+		return &WhileStmt{&Literal{true}, p.statement()}
+	}
+
+	p.consume(LEFT_PAREN, "Expect '(' after 'for'.")
+
+	var init Stmt
+
+	if p.match(SEMICOLON) {
+		init = nil
+	} else if p.match(VAR) {
+		init = p.varDecl()
+	} else {
+		init = p.exprStmt()
+	}
+
+	var cond Expr
+
+	if !p.check(SEMICOLON) {
+		cond = p.expression()
+	}
+
+	p.consume(SEMICOLON, "Expect ';' after for loop condition;")
+
+	var incr Expr
+
+	if !p.check(RIGHT_PAREN) {
+		incr = p.expression()
+	}
+
+	p.consume(RIGHT_PAREN, "Expect ')' after for clauses;")
+
+	var body = p.statement()
+
+	if incr != nil {
+		body = &BlockStmt{[]Stmt{body, &ExprStmt{incr}}}
+	}
+
+	if cond == nil {
+		cond = &Literal{true}
+	}
+
+	body = &WhileStmt{cond, body}
+
+	if init != nil {
+		body = &BlockStmt{[]Stmt{init, body}}
+	}
+
+	return body
+}
+
 // env -> "env" ";"
 func (p *Parser) envStmt() Stmt {
 	p.consume(SEMICOLON, "Expect ';' after 'env'.")

tests/for.lox

@@ -0,0 +1,36 @@
+
+print "full form -------------------------";
+for (var i = 0; i < 100; i = i + 20) print i;
+
+print "without init ----------------------";
+var n = 100;
+for (;n > 0; n = n - 20) print n;
+
+print "only cond -----------------------";
+
+var i = 1;
+for (;i < 100;) {
+    print i;
+    i = i + 10;
+}
+
+print "inf ---------------------------";
+
+var b = 0;
+for {
+    print b;
+    b = b + 5;
+    if (b > 10) break;
+
+    print "after break";
+}
+
+print "fibonachi ------------------------";
+var temp;
+var first = 0;
+
+for (var second = 1; first < 10000; second = temp + second) {
+    print first;
+    temp  = first;
+    first = second;
+}

tests/while.lox

@@ -12,17 +12,24 @@ var iterator = 100;
 
 {
     while (iterator < 100) {
+        {
             {
                 print iterator;
                 iterator = iterator + 2;
 
-            if (iterator > 50) {
+                if (iterator > 50) break;
-                break;
-            }
 
                 print "shoud not be printed after 50";
             }
+
+            print "OUTER also shoud not be printed after 50";
+
+        }
     }
 }
 
+while (iterator < 100) iterator = iterator + 2; 
+
+
+
 print iterator;