String.{starts,ends}_with: use the label sub instead of prefix and suffix

[gasche]

This is a continuation of #9533 and #10105, a change proposal for String.{starts,ends}_with that had support from both @bschommer and @dbuenzli: use the ~sub label for both functions instead of ~prefix for one and ~suffix for the other.

I also changed ocamlmklib to use the standard library functions instead of a local reimplementation. It's interesting to see the impact of the change (the callsites do feel more verbose).

I must say that I find this change less convincing than #10127. To me the function calls do read slightly more nicely with the current label names than with the new ~sub labels.

[darioteixeira]

I agree that the label names prefix and suffix are way more readable and intuitive than sub.

[dbuenzli]

If people prefer to keep it that way I don't mind but then one should think that there is still String.includes and a function to find the location of a substring in a larger one, say String.find_sub (feel free to find another name) that need to be added -- which in my opinion should be added now using the trivial n^2 algorithm with a warning that it does so. Labels for these will have to be found aswell and it's good to think about the whole package.

Here are two proposal, one with sub prefixes and one with per function specific labelling.

(* 1 *)
String.starts_with : sub:string -> string -> bool
String.includes : sub:string -> string -> bool
String.ends_with : sub:string -> string -> bool
String.find_sub : ?start:int -> sub:string -> string -> int option 
String.sub : string -> int -> int -> string

(* 2 *)
String.starts_with : prefix:string -> string -> bool 
String.includes : affix:string -> string -> bool
String.ends_with : suffix:string -> string -> bool
String.find_sub : ?start:int -> needle:string -> string -> int option 
String.sub : string -> int -> int -> string

[Octachron]

It seems fine to me to revert to the generic label, sub (or substr), when there is no better specialized term:

Stringstarts_with : prefix:string -> string -> bool 
String.includes : sub:string -> string -> bool
String.ends_with : suffix:string -> string -> bool
String.find_sub : ?start:int -> sub:string -> string -> int option 
String.sub : string -> int -> int -> string

[xavierleroy]

This use of sub was already proposed, discussed, and rejected in #9820. How many times do we need to propose, discuss, and reject this? We are running in circles.

[gasche]

Okay, okay. Don't shoot! I'll close this as I'm not convinced myself.