provides a update function for map

[vicuna]

Original bug ID: 7309
Reporter: @bobzhang
Status: resolved (set by @alainfrisch on 2017-02-28T13:15:59Z)
Resolution: fixed
Priority: normal
Severity: feature
Fixed in version: 4.06.0 +dev/beta1/beta2/rc1
Category: standard library
Has duplicate: #8223
Related to: #5220
Monitored by: "Boris Yakokobowski"

Bug description

type would be

val update: key -> ('a option -> 'a) -> 'a t -> 'a t

the rational is mostly for performance, this API is also available in Haskell

https://downloads.haskell.org/~ghc/6.12.3/docs/html/libraries/containers-0.3.0.0/Data-Map.html#6

[vicuna]

Comment author: @alainfrisch

I'd be interested to see benchmarks to illustrate the gains. Avoiding an extra (allocation-free) lookup could be somehow compensated by the extra allocations for the closure and the option type. Or could flambda get rid of them?

[vicuna]

Comment author: @bobzhang

note that exception is not cheap in JS backend, while update is a quite common paradigm,
I am in favor of having a update function which does not rely on exception, but it is still a good step that we have a update function whether it relies on exception or not

[vicuna]

Comment author: @alainfrisch

#1026