CODEWITHSUNDEEP
ocaml
asfe
asfe

Reputation: 63

Scope of variables in OCaml

When I have e.g.

type 'a inf_list = Cons of 'a * (unit -> inf_list);; 

(* inf_list starting at n*)
let rec num n = Cons (n, fun () -> num (n+1));;

How does the following work:

let Cons (cur, rest_l) = integers 1;; 

let x = cur;; 
let y = (rest_l());;

normally the format is let <variable/function-name> = <definition>.

Here it is let <type (x,y) = <expression>. So generally speaking how does this work?

Upvotes: 1

Views: 146

Answers (2)

Chris
Chris

Reputation: 36516

As an addendum to Jeffrey's answer, please note that the as keyword can be used to bind a name to a pattern.

In your case:

let Cons (cur, rest_l) as lst = integers 1;;

Where lst now refers to the entire inf_list value as well as binding names to its constituent values.

Upvotes: 1

Jeffrey Scofield
Jeffrey Scofield

Reputation: 66793

First of all, the form for let is let <pattern> = <expression>. You can have many things in a let besides variable and function names. A name is just one possible kind of pattern.

Second, the subexpression Cons (cur, rest_l) is not a type. It's a pattern that matches a value of type 'a inf_list. The head of the list will be bound to cur and the rest of the list will be bound to rest_l.

So your example has the expected form for a let. And it binds the two names cur and rest_l in the global scope.

Upvotes: 2

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