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Compare with Seq instead of Gen.

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Drup 2019-03-08 18:41:47 +01:00
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@ -178,25 +178,19 @@ example library. It requires OCaml>=4.0 to compile, because of the GADT
structure used in the monadic parser combinators part of `examples/sexpr.ml`. structure used in the monadic parser combinators part of `examples/sexpr.ml`.
Be careful that this is quite obscure. Be careful that this is quite obscure.
## Comparison with [gen](https://github.com/c-cube/gen) ## Comparison with `Seq` from the standard library
- `Gen` is an *external* iterator. - `Seq` is an *external* iterator.
It means that the code which consumes It means that the code which consumes
some iterator of type `'a Gen.t` is the one which decides when to some iterator of type `'a Seq.t` is the one which decides when to
go to the next element. This gives a lot of flexibility, for example go to the next element. This gives a lot of flexibility, for example
when iterating on several iterators at the same time: when iterating on several iterators at the same time:
```ocaml ```ocaml
let zip (g1: 'a Gen.t) (g2:'b Gen.t) : ('a * 'b) Gen.t = let rec zip a b () = match a(), b() with
let x1 = ref (g1 ()) in | Nil, _
let x2 = ref (g2 ()) in | _, Nil -> Nil
fun () -> match !x1, !x2 with | Cons (x, a'), Cons (y, b') -> Cons ((x,y), zip a' b')
| None, _ | _, None -> None
| Some x, Some y ->
(* fetch next elements from g1 and g2 *)
x1 := g1 ();
x2 := g2 ();
Some (x,y)
``` ```
- `Iter` is an *internal* iterator. When one wishes to iterate over - `Iter` is an *internal* iterator. When one wishes to iterate over
@ -206,10 +200,10 @@ Be careful that this is quite obscure.
This makes `zip` impossible to implement. However, the type `'a Iter.t` This makes `zip` impossible to implement. However, the type `'a Iter.t`
is general enough that it can be extracted from any classic `iter` function, is general enough that it can be extracted from any classic `iter` function,
including from data structures such as `Map.S.t` or `Set.S.t` or `Hashtbl.t`; including from data structures such as `Map.S.t` or `Set.S.t` or `Hashtbl.t`;
one cannot obtain a `'a Gen.t` from these without having access to the internal one cannot obtain a `'a Seq.t` from these without having access to the internal
data structure. data structure.
In short, `'a Gen.t` is more expressive than `'a Iter.t`, but it also In short, `'a Seq.t` is more expressive than `'a Iter.t`, but it also
requires more knowledge of the underlying source of items. requires more knowledge of the underlying source of items.
For some operations such as `map` or `flat_map`, Iter is also extremely For some operations such as `map` or `flat_map`, Iter is also extremely
efficient and will, if flambda permits, be totally removed at efficient and will, if flambda permits, be totally removed at