+ ((lambda (z) (+ 2 z)) (* y x)))
+ 67) ; exit code modulos at 256
+(test-prog '(if ((lambda (x) (= x 2)) 1) 0 (- 32 1)) 31)
+
+(test-prog-stdout '(if (= 3 2) 1 (let () (print "hello world!") 0)) "hello world!")
+
+(test-prog '((lambda (x y) (+ x y)) 1 2) 3)
+(test-prog '((lambda (x) (+ ((lambda (y) (+ y 1)) 3) x)) 2) 6)
+
+ ; passing closures about
+(test-prog '((lambda (z) ((lambda (x) (x 1)) (lambda (y) (+ z y)))) 2) 3)