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ass5: prime lift,bind,add
[lambda.git]
/
assignment5.mdwn
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b/assignment5.mdwn
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assignment5.mdwn
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assignment5.mdwn
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-127,19
+127,19
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Baby monads
-----------
Read the lecture notes for week 6, then write a
-----------
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
+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,
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
+`lift
'
` will have type
(int -> int -> int) -> (int option) -> (int option) -> (int option)
(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.
Don't worry about why you need to put `+` inside of parentheses.
-You should make use of `bind
` in your definition of `lift
`:
+You should make use of `bind
'` in your definition of `lift'
`:
- let bind (x: int option) (f: int -> (int option)) =
+ let bind
'
(x: int option) (f: int -> (int option)) =
match x with None -> None | Some n -> f n;;
match x with None -> None | Some n -> f n;;