erg/doc/EN/syntax/28_spread_syntax.md

Spread assignment

In a spread assignment, a variable can be prefixed with ... in front of the variable, all the remaining elements can be expanded into the variable. This is called a spread assignment.

[x, ... .y] = [1, 2, 3]
assert x == 1
assert y == [2, 3].
x, ... .y = (1, 2, 3)
assert x == 1
assert y == (2, 3)

Extract assignment

If nothing is written after ..., the remaining elements are ignored and an assignment is made. This type of expansion assignment is specifically called an extract assignment. Extract assignment is a useful syntax for bringing certain attributes local to a module or record.

{sin; cos; tan; ...} = import "math"

This way, sin, cos, tan can be used locally from then on.

You can do the same with records.

record = {x = 1; y = 2}
{x; y; ...} = record

If you want to expand all of them, use {*} = record, this is equivalent to open in OCaml and so on.

record = {x = 1; y = 2}
{*} = record
assert x == 1 and y == 2

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