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doc: add some doc about gen

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close #19
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Simon Cruanes 2019-12-14 14:56:57 -06:00
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README.md
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@ -181,7 +181,7 @@ 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 `Seq` from the standard library ## Comparison with `Seq` from the standard library, and with `Gen`
- `Seq` is an *external* iterator. - `Seq` is an *external* iterator.
It means that the code which consumes It means that the code which consumes
@ -206,6 +206,14 @@ Be careful that this is quite obscure.
one cannot obtain a `'a Seq.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.
- `Gen` (from [the gen library](http://github.com/c-cube/gen))
is an *external* iterator, like `Seq`, but it is imperative, mutable, and consumable
(you can't iterate twice on the same `'a Gen.t`).
It looks a lot like iterators in rust/java/… and can be pretty efficient in some cases.
Since you control iteration you can also write `map2`, `for_all2`, etc but
only with linear use of input generators (since you can traverse them only once).
That requires some trickery for cartesian_product (like storing already produced elements internally).
In short, `'a Seq.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
@ -213,8 +221,9 @@ efficient and will, if flambda permits, be totally removed at
compile time (e.g. `Iter.(--)` becomes a for loop, and `Iter.filter` compile time (e.g. `Iter.(--)` becomes a for loop, and `Iter.filter`
becomes a if test). becomes a if test).
For more details, you can read http://gallium.inria.fr/blog/generators-iterators-control-and-continuations/ . For more details, you can read http://gallium.inria.fr/blog/generators-iterators-control-and-continuations/ or
see [the slides about Iter](https://simon.cedeela.fr/assets/talks/sequence.pdf)
by me (c-cube) when `Iter` was still called `Sequence`.
## Build ## Build