jaja lang

[
	cb:
	node:

	node;"value".cb;!

	node;"left".nil=~[node;$"left".cb;visit;!node:]?
	node;"right".nil=~[node;$"right".cb;visit;!node:]?
]visit:

\d: d; "value" 4 ,
\e: e; "value" 5 ,
\f: f; "value" 6 ,
\g: g; "value" 7 ,

\b: b; "value" 2 , b;"left"d;, b;"right"e;,
\c: c; "value" 3 , c;"left"f;, c;"right"g;,

\a: a; "value" 1 , a;"left"b;, a;"right"c;,

a; ["value: "print;!println;!] visit;!



this program prints:

value: 1
value: 2
value: 4
value: 5
value: 3
value: 6
value: 7