1 files changed, 24 insertions, 0 deletions
diff --git a/monad/stack.scm b/monad/stack.scm
new file mode 100644
index 0000000..8d25303
--- /dev/null
+++ b/monad/stack.scm
@@ -0,0 +1,24 @@
+(define-module (monad stack)
+  #:export (pop peek push)
+  #:use-module (monad)
+  #:use-module (monad state))
+
+;;; Simple stateful stack module for showing the state monad
+;;; in action. These functions assume that they are in a
+;;; (state list) monad. But dynamic types!
+
+;;; TODO test these for empty stack
+
+(define (pop)
+  (do st <- (get)
+      let top = (car st)
+      (put (cdr st))
+      (return-state top)))
+
+(define (peek)
+  (do st <- (get)
+      (return-state (car st))))
+
+(define (push v)
+  (do st <- (get)
+      (put (cons v st))))