for-generator example

examples/for-generator.ks

@@ -0,0 +1,19 @@
+use std.*;
+
+let generator = fn(()) {
+	print "yielding 1";
+	yield "1";
+	print "yielding 2";
+	yield "2";
+	print "yielding stop";
+	yield "stop";
+	print "yielding 3";
+	yield "3";
+};
+
+for value in generator() {
+	print value;
+  #if value == "stop" {
+    #break;
+  #}
+};

std/lib.ks

@@ -93,3 +93,17 @@ impl float64 as Parse = (
 const parse = forall[T] {
   (T as Parse).parse
 };
+
+const generator_handler = forall[T] {
+  (.handle = T -> () with ()) :: type
+};
+
+impl syntax @"syntax".for_loop = macro (.value_pattern, .generator, .body) => `(
+  with (.handle = $value_pattern => $body) :: generator_handler[_];
+  $generator
+);
+
+impl syntax @"syntax".@"yield" = macro (.value) => `(
+  (current generator_handler[_]).handle $value
+);
+

std/syntax.ks

@@ -15,9 +15,10 @@ syntax_module {
   # syntax break_with_value <- 2 = "break" value;
   # syntax break_without_value <- 2 = "break";
   # syntax continue_impl <- 2 = "continue";
+  syntax yield <- 2 = "yield" value;
 
   # syntax loop_impl <- 3 = "loop" "{" body "}";
-  # syntax for_loop <- 3 = "for" value_pattern "in" generator "{" body "}";
+  syntax for_loop <- 3 = "for" value_pattern "in" generator "{" body "}";
   syntax @"builtin macro impl_cast" <- 4 = "impl" value "as" target "=" impl;
   syntax @"builtin macro impl_syntax" <- 4 = "impl" "syntax" def "=" impl;
   syntax @"builtin macro let" <- 4 = "let" pattern "=" value;