CODEWITHSUNDEEP
syntaxfunctional-programmingocaml
obla
obla

Reputation: 123

'==' type and pattern matching - wait for the other recursive calls and do nothing on a case

I have two questions concerning OCaml. Firstly, what does the == means when defining a type.

For example you can see at the end of this page the following code:

type compteur == int;;

Then what is the difference with:

type compteur = int;;

Moreover I have an other question concerning pattern matching. How to say that you want to return nothing on a case.

For example let's say I have a function f that returns a boolean:

let rec f v = function 
     | t when t<v -> true
     | t when t > v -> f (t-1)
     | t when t = v -> (* here a code to say that you do nothing, and wait for the other recursive call *)

Upvotes: 2

Views: 79

Answers (1)

sepp2k
sepp2k

Reputation: 370122

type compteur == int is a syntax error. The only valid way to define a type alias is with =, not ==. It's just a typo on the page you linked.

How to say that you want to return nothing on a case.

The only way to return nothing from a function would be to exit the program, raise an exception or loop (or recur) infinitely. Otherwise a function always returns a value.

here a code to say that you do nothing, and wait for the other recursive call

What other recursive call? In the case that t = v only the code for that case will run. There is no other code to wait on.

Upvotes: 3

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