X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment5.mdwn;h=3989928996c6042a1ba4b155236310aad4a6d5a5;hp=fee1d8334575bbdefdd4f8572b2aafc3f62e6531;hb=7b00a5a3dc3f7208f67ed5c87faf22b351e14b0c;hpb=74c28ae2bdc6692628a47f6bb383d0777256b930 diff --git a/assignment5.mdwn b/assignment5.mdwn index fee1d833..39899289 100644 --- a/assignment5.mdwn +++ b/assignment5.mdwn @@ -210,7 +210,7 @@ value to give back if the argument is the empty list. Ultimately, we might want to make use of our `'a option` technique, but for this assignment, just pick a strategy, no matter how clunky. -Be sure to test your proposals with simple lists. (You'll have to make_list +Be sure to test your proposals with simple lists. (You'll have to `make_list` the lists yourself; don't expect OCaml to magically translate between its native lists and the ones you buil.d) @@ -233,20 +233,20 @@ any auxiliary functions you need. Baby monads ----------- -Read the lecture notes for week 6, then 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 +Read the material on dividing by zero/towards monads from the end of lecture +notes for week 6 the start of lecture notes for week 7, then 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: (int -> int -> int) -> (int option) -> (int option) -> (int option) -so that `lift' (+) (Some 3) (Some 4)` will evalute to `Some 7`. +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'`: - let bind' (x: int option) (f: int -> (int option)) = - match x with None -> None | Some n -> f n;; + let bind' (u: int option) (f: int -> (int option)) = + match u with None -> None | Some x -> f x;;