CODEWITHSUNDEEP
exceptionstreamtry-catchocaml
user0
user0

Reputation: 195

OCaml Streams: exception handling or Option types?

To handle exceptional cases in OCaml, it is often possible to choose to either catch exceptions or to use the type 'a option. If I understand correctly, both choices are possible for Streams thanks to the functions Stream.next (raises an exception) and Stream.peek/Stream.junk (return 'a option).

Is there any difference between

match Stream.peek t with
| None -> ***
| Some c -> Stream.junk t; *****

and

try
  let c = Stream.next t in *****
with Stream.Failure -> ***

where t is a variable of type 'a stream and *** and ***** are some sequences of expressions?

Edit 2020-12-03

Since OCaml 4.02, it is also possible to write the above as

match Stream.next t with
| c -> *****
| exception Stream.Failure -> ***

which may be preferable if further pattern matching is to be done on c, e.g.,

match Stream.next t with
| [] -> *****
| a::b -> *******
| exception Stream.Failure -> ***

(source: Xavier Leroy's slides What's new in OCaml 4.02).

Upvotes: 1

Views: 339

Answers (1)

Jeffrey Scofield
Jeffrey Scofield

Reputation: 66823

There is no difference in behavior, as you note.

The version with an option type will cons up some more data, as it has to create Some x for each value returned. This will be a minor effect in general because OCaml is excellent at garbage collecting short-lived values.

I personally like using options because of the parallelism between the two cases. But using peek and junk seems quite a bit clunkier than just having a function that returns an option. So for this case I might use the exception-based handling.

In other words, it's a judgement call (in my opinion).

Upvotes: 2

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