pulled in lisp koans for solving

https://github.com/google/lisp-koans

lisp-koans/koans/let.lisp

@@ -0,0 +1,62 @@
+;;; Copyright 2013 Google Inc.
+;;;
+;;; Licensed under the Apache License, Version 2.0 (the "License");
+;;; you may not use this file except in compliance with the License.
+;;; You may obtain a copy of the License at
+;;;
+;;;     http://www.apache.org/licenses/LICENSE-2.0
+;;;
+;;; Unless required by applicable law or agreed to in writing, software
+;;; distributed under the License is distributed on an "AS IS" BASIS,
+;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;;; See the License for the specific language governing permissions and
+;;; limitations under the License.
+
+(define-test let
+  ;; The LET form establishes a lexical extent within which new variables are
+  ;; created: a symbol that names a variable becomes bound to a value.
+  (let ((x 10)
+        (y 20))
+    (assert-equal ____ (+ x y))
+    ;; It is possible to shadow previously visible bindings.
+    (let ((y 30))
+      (assert-equal ____ (+ x y)))
+    (assert-equal ____ (+ x y)))
+  ;; Variables bound by LET have a default value of NIL.
+  (let (x)
+    (assert-equal ____ x)))
+
+(define-test let-versus-let*
+  ;; LET* is similar to LET, except the bindings are established sequentially,
+  ;; and a binding may use bindings that were established before it.
+  (let ((x 10)
+        (y 20))
+    (let ((x (+ y 100))
+          (y (+ x 100)))
+      (assert-equal ____ x)
+      (assert-equal ____ y))
+    (let* ((x (+ y 100))
+           (y (+ x 100)))
+      ;; Which X is used to compute the value of Y?
+      (assert-equal ____ x)
+      (assert-equal ____ y))))
+
+(define-test let-it-be-equal
+  ;; Fill in the LET and LET* to get the tests to pass.
+  (let ((a 1)
+        (b :two)
+        (c "Three"))
+    (let ((____ ____)
+          (____ ____)
+          (____ ____))
+      (assert-equal a 100)
+      (assert-equal b 200)
+      (assert-equal c "Jellyfish"))
+    (let* ((____ ____)
+           (____ ____)
+           ;; In this third binding, you are allowed to use the variables bound
+           ;; by the previous two LET* bindings.
+           (____ ____))
+      (assert-equal a 121)
+      (assert-equal b 200)
+      (assert-equal c (+ a (/ b a))))))