0004952: wish: after functions in ordered types like Map or Set

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0004952

OCaml

OCaml general

public

2010-01-02 19:49

2010-01-07 15:47

Reporter

Basile Starynkevitch

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Priority

normal

Severity

feature

Reproducibility

have not tried

Status

acknowledged

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open

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Fixed in Version

Summary

0004952: wish: after functions in ordered types like Map or Set

Description

Il would be quite useful to be able to get, inside a Map, the entry (if any) after a given key.

So I would dream of an additional function inside Map.S

(** [after k m] retrieve the next key, that is the lowest [nk] such that the map [m] contains a binding for [nk] and with [nk] compared greater than [k]. If no such key exist, raises [Not_found] **)
val after: key -> 'a t -> key

Likewise, it would be useful to be able to get, inside a Set, the element (if any) next to a given one.

So I would dream of an additional function inside Set.S

(** [next x s] returns the element [y] after the given [x] in set [s], or raises [Not_found] if no such element exist (i.e. if [s] is empty or if [x] is the maximal element. *)
val next: elt -> t -> elt

Additional Information

The wished Set.S.next can be defined using Set.S.split (but that might not be efficient) and Set.S.min.

One could also wish the dual Set.S.previous.

Both functions have the following uses:

* the notion of good orders in math.

* in general, implement iterating co-routines (or iteration in CPS style) in Set-s or Map-s.

* in particular, they would be quite useful in some graphical interface applications. For example, suppose one code an editor using LabGtk & GText.buffer & GText.view. If one wants to have some sensitive words or text fragments, it would be useful to find e.g. the iter after a given line, etc..

Happy New Year 2010!

Regards.

--
Basile Starynkevitch

Issue History
Date Modified	Username	Field	Change
2010-01-02 19:49	Basile Starynkevitch	New Issue
2010-01-07 15:47	doligez	Status	new => acknowledged

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