--- a/midterm/src/stack.agda.replace	Thu Oct 26 15:04:10 2017 +0900
+++ b/midterm/src/stack.agda.replace	Fri Oct 27 17:06:15 2017 +0900
@@ -1,5 +1,12 @@
+record Stack {a t : Set} (stackImpl : Set) : Set  where
+field
+stack : stackImpl
+push  : stackImpl -> a -> (stackImpl -> t) -> t
+pop   : stackImpl -> (stackImpl -> Maybe a -> t) -> t
+open Stack
+
 pushStack : {a t : Set} -> Stack a -> a -> (Stack t -> t) -> t
 pushStack {a} {t} s0 d next = (push s0) (stack s0) d (\s1 -> next (record {stack = s1} ))
 
 popStack : {a t : Set} -> Stack a -> (Stack t -> t) -> t
-popStack {a} {t} s0 next = (pop s0) (stack s0) (\s1 -> next s0)
\ No newline at end of file
+popStack {a} {t} s0 next = (pop s0) (stack s0) (\s1 -> next s0)