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OCaml's parser syntax for F#?
f#

I've yet to play with F#'s lazy list module, but I thought maybe the parser syntax might be worth making a standard part of F# (in ocaml, camlp4o is needed to use the syntax though). [< ... >] is the syntax for building lazy lists (ocaml streams).

E.g, a very simple example of lazy fib using streams:

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let fib () = let rec fib a b = let c = a + b in [< 'a; fib b c >] in fib 1 1;;

Having a nice syntax for pretty-printing lazy lists would be nice too!

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Hmm, I should probably show an example of using the parser keyword too...

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let rec zip = parser
  | [< 'x; s1 >] -> begin parser
    | [< 'y; s2 >] -> [< '(x,y); zip s1 s2 >]
    | [< >] -> [< >]
    end
  | [< >] -> fun _ -> [< >];;

Gives: val zip : 'a Stream -> 'b Stream -> ('a * 'b) Stream in OCaml.

I don't see anyway to use tuples of streams with the parser keyword, hence the nesting; however, it's quite similar to normal lists, except now they're lazy!

By on 6/17/2006 1:31 AM ()

Hi,

It's important to note that OCaml's "Stream"s aren't Haskell-style lazy lists - they are a form of imperative stream much like .NET IEnumerable values, though with lookahead, and are suitable for some parsing applications. (Avoiding the name clash is one reason why we recently switched the F# names for lazy lsits from Stream to LazyList).

If you're after operations on IEnumerable data streams then take a look at the definitions in the existing IEnumerable module. Ienumerable.unfold is an especially powerful function.

Cheers!

Don

By on 6/17/2006 11:06 AM ()

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