Added support for LFE (Lisp Flavored Erlang).

samples/LFE/church.lfe

@@ -0,0 +1,111 @@
+;; Copyright (c) 2013 Duncan McGreggor <oubiwann@cogitat.io>
+;;
+;; 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.
+
+;; File    : church.lfe
+;; Author  : Duncan McGreggor
+;; Purpose : Demonstrating church numerals from the lambda calculus
+
+;; The code below was used to create the section of the user guide here:
+;;    http://lfe.github.io/user-guide/recursion/5.html
+;;
+;; Here is some example usage:
+;;
+;; > (slurp '"church.lfe")
+;; #(ok church)
+;; > (zero)
+;; #Fun<lfe_eval.10.53503600>
+;; > (church->int1 (zero))
+;; 0
+;; > (church->int1 (three))
+;; 3
+;; > (church->int1 (five))
+;; 5
+;; > (church->int2 #'five/0)
+;; 5
+;; > (church->int2 (lambda () (get-church 25)))
+;; 25
+
+(defmodule church
+  (export all))
+
+(defun zero ()
+  (lambda (s)
+    (lambda (x) x)))
+
+(defun one ()
+  (lambda (s)
+    (lambda (x)
+      (funcall s x))))
+
+(defun two ()
+  (lambda (s)
+    (lambda (x)
+      (funcall s
+        (funcall s x)))))
+
+(defun three ()
+  (lambda (s)
+    (lambda (x)
+      (funcall s
+        (funcall s
+          (funcall s x))))))
+
+(defun four ()
+  (lambda (s)
+    (lambda (x)
+      (funcall s
+        (funcall s
+          (funcall s
+            (funcall s x)))))))
+
+(defun five ()
+  (get-church 5))
+
+(defun int-successor (n)
+  (+ n 1))
+
+(defun church->int1 (church-numeral)
+  "
+  Converts a called church numeral to an integer, e.g.:
+  > (church->int1 (five))
+  "
+  (funcall
+    (funcall church-numeral #'int-successor/1) 0))
+
+(defun church->int2 (church-numeral)
+  "
+  Converts a non-called church numeral to an integer, e.g.:
+  > (church->int2 #'five/0)
+  "
+  (funcall
+    (funcall
+      (funcall church-numeral) #'int-successor/1) 0))
+
+(defun church-successor (church-numeral)
+  (lambda (s)
+    (lambda (x)
+      (funcall s
+        (funcall
+          (funcall church-numeral s) x)))))
+
+(defun get-church (church-numeral count limit)
+  (cond ((== count limit) church-numeral)
+        ((/= count limit)
+         (get-church
+           (church-successor church-numeral)
+           (+ 1 count)
+           limit))))
+
+(defun get-church (integer)
+  (get-church (zero) 0 integer))