add replace function

[EmileTrotignon]

Add a replace function to address issue #26

[Drup]

Thanks for the patch !

oh, wow, it took me several time to understand what you were going for ... It's impressively elegant in term of implementation, but my gut feeling is that it's a horrible API. This is reinforced by the need for a one-way converter.

Why not something of the form 'a Tyre.t -> ('a -> string) -> string -> (string, _) error instead ? Or even simpler string Tyre.t -> (string -> string) -> string -> (string, _) error

Overall, I agree it's a very interesting to add replace, but I must say it's not clear to me what we gain over just using Re.

[EmileTrotignon]

It's impressively elegant in term of implementation, but my gut feeling is that it's a horrible API. This is reinforced by the need for a one-way converter.

I guess my idea was to use regexp without having to do anything outside it, but its true that in this case having an 'a -> string parameter is good because you do not need it both ways for replace, which conv requires. It will also not make the implementation very different.

I must say it's not clear to me what we gain over just using Re.

A lot ! Even if the regexp returns a string at the end, does not mean you cannot use the typing in the middle. In the test I wrote for instance, I multiply every int in a string by two. Doing that with Re would require unsafe calls to int_of_string.
Anyway, I want to use Tyre with everything, even for use-cases where Re is just as good, because what if I need to do more complex stuff later and then the typing is critical ?