Propose some list built-in improvements now that we have a stdlib

[AltGr]

Remove the sum builtins (and replace by stdlib functions)

Since it's not overloaded and requires an explicit type with a custom syntax sum money of [...], this built-in could easily be replaced by per-type stdlib functions: Money.sum content money depends on l content list of money, etc.
In this new context there is no real justification for a custom syntax.

Find in a list using a predicate

This is a pretty common operation, but it requires a predicate which is not possible at the moment with stdlib functions. At the moment, this is how it can be done:

let candidates equals
  list of element among lst such that predicate of element
in
List.first_element of candidates

This returns an optional as expected; but it is a bit verbose, which obfuscates the point.

Depending on how common this really is, it should be considered to add a new builtin such as:

find element among lst such that predicate of element

More

This is open for discussions and more suggestions.

[avh-cnaf]

Some ideas:

• shorter, not-able:
  elements of lst such that [not] predicate

• companions keywords:
  first of lst such that [not] predicate
only of lst such that [not] predicate --> retrieves an element or crash, not a optional

Composables predicates:

• not aware of how it works in ocaml, but coming from java i've found it pretty really really cool to use:
  predicate_4 = predicate1.and(predicate2).not( predicate3)
  with variants: OR,NOT,NEGATE

In another tool i've been able to word/use the java predicate interface and the functional one, it has been fantastic in terms of what it can achieves: nice/not that bad wording for even very complex logic.