adding lisp-interpreter

lisp-interpreter/tests/code/permute.scm

@@ -0,0 +1,21 @@
+(define (brute max-length set)
+  (define (permute n)
+    (define str (make-string n))
+    (define (iter d)
+      (if (= d n)
+        (begin 
+          (display str)
+          (display " "))
+        (do ((i 0 (+ i 1)))
+          ((= i (string-length set)) 'done)
+           (begin
+             (string-set! str d (string-ref set i))
+             (iter (+ d 1))))))
+      (iter 0))
+
+    (do ((len 0 (+ len 1)))
+      ((> len max-length) 'done)
+      (permute len)))
+
+(brute 4 "abcd")
+(newline)