X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=exercises%2F_assignment7.mdwn;h=793a15e46c8715b5f99f5ac833f5c6e59fc96456;hp=cd798ab078ad9b86f986a8f40d396a487b579c3b;hb=a7f15a6a8100c10bde1cf7b97a02660a3d00b9d9;hpb=ef351afc1578508e294f73be1c2f2445463d6383

diff --git a/exercises/_assignment7.mdwn b/exercises/_assignment7.mdwn
index cd798ab0..793a15e4 100644
--- a/exercises/_assignment7.mdwn
+++ b/exercises/_assignment7.mdwn
@@ -1,25 +1,18 @@
-# Assignment 6 (week 7)
+## Baby monads
 
-## Evaluation order in Combinatory Logic
+(Depends on lecture notes for safe division by zero.)
 
-1. Give a term that the lazy evaluators (either the Haskell evaluator,
-or the lazy version of the OCaml evaluator) do not evaluate all the
-way to a normal form, i.e., that contains a redex somewhere inside of
-it after it has been reduced.
+Write a function `lift'` that generalized the correspondence between +
+and `add'`: that is, `lift'` takes any two-place operation on integers
+and returns a version that takes arguments of type `int option`
+instead, returning a result of `int option`.  In other words, `lift'`
+will have type:
 
-<!-- reduce3 (FA (K, FA (I, I))) -->
+	(int -> int -> int) -> (int option) -> (int option) -> (int option)
 
+so that `lift' (+) (Some 3) (Some 4)` will evalute to `Some 7`.
+Don't worry about why you need to put `+` inside of parentheses.
+You should make use of `bind'` in your definition of `lift'`:
 
-2. One of the 
-[[criteria we established for classifying reduction strategies|
-topics/week3_evaluation_order]]
-strategies is whether they reduce subexpressions hidden under lambdas.
-That is, for a term like `(\x y. x z) (\x. x)`, do we reduce to
-`\y.(\x.x) z` and stop, or do we reduce further to `\y.z`?  Explain
-what the corresponding question would be for CL. Using either the
-OCaml CL evaluator or the Haskell evaluator developed in the wiki
-notes, prove that the evaluator does reduce expressions inside of
-"functional" CL expressions.  Then provide a modified evaluator that
-does not perform reductions in those positions.
-
-<!-- just add early no-op cases for Ka and Sab -->
+	let bind' (u: int option) (f: int -> (int option)) =
+		match u with None -> None | Some x -> f x;;