Closure, coin sums, & number spiral generator

2 files changed, 91 insertions, 0 deletions

diff --git a/closure/closure-test.scm b/closure/closure-test.scm
new file mode 100644
index 0000000..ae10b67
--- /dev/null
+++ b/closure/closure-test.scm
@@ -0,0 +1,59 @@
+;; -*- compile-command: "guile -L . closure-test.scm"; -*-
+(use-modules (srfi srfi-64)
+             (closure))
+
+(define iterative-add-generator-1
+  (iterative-add))
+
+(define iterative-add-generator-2
+  (iterative-add))
+
+(test-begin "harness")
+
+(test-equal "add 0 to 1"
+  1
+  (iterative-add-generator-1 1))
+
+(test-equal "add 1 to 2"
+  3
+  (iterative-add-generator-1 2))
+
+(test-equal "add 2 to 6"
+  8
+  (iterative-add-generator-1 6))
+
+(test-equal "add 6 to 5"
+  11
+  (iterative-add-generator-1 5))
+
+(test-equal "add 0 to 2"
+  2
+  (iterative-add-generator-2 2))
+
+(test-equal "add 2 to 2"
+  4
+  (iterative-add-generator-2 2))
+
+
+(set-store (string->list "abcdefghijklmnopqrstuvwxyz"))
+
+;;; never returns, but manual validation shows
+;;; the function works. Bug in testing library?
+;; (test-equal "peek-char first"
+;;   #\a
+;;   (peek-char))
+
+(test-equal "advance-char first"
+  #\a
+  (advance-char))
+
+(test-equal "advance-char second"
+  #\b
+  (advance-char))
+
+;; (test-equal "peek-char second"
+;;   #\c
+;;   (peek-char))
+
+
+(test-end "harness")
diff --git a/closure/closure.scm b/closure/closure.scm
new file mode 100644
index 0000000..9dec47e
--- /dev/null
+++ b/closure/closure.scm
@@ -0,0 +1,32 @@
+(define-module (closure)
+  #:export (iterative-add
+            set-store
+            peek-store
+            advance-char))
+
+(define (iterative-add)
+  "Given NUM, returns NUM plus the previous
+supplied NUM."
+  (let ((prev-num 0))
+    (lambda num
+      (let ((result
+             (+ (car num) prev-num)))
+        (set! prev-num (car num))
+        result))))
+
+(define set-store #f)
+(define peek-char #f)
+(define advance-char #f)
+
+(let ((store '()))
+  (set! set-store
+        (lambda (lst)
+          (set! store lst)))
+  (set! peek-char
+        (lambda ()
+          (car store)))
+  (set! advance-char
+        (lambda ()
+          (let ((ret (car store)))
+            (set! store (cdr store))
+            ret))))