tree 33f54e87dbefe72a6081b41534738f1639e0d19f
parent ff48658e696010c572072ddd114c8435cd4b7c5b
author Marcel van Lohuizen <mpvl@golang.org> 1609670886 +0100
committer Marcel van Lohuizen <mpvl@golang.org> 1610198965 +0000

doc/ref/spec.md: get rid of list operators

List operators are confusing. For instance,
is the result of [a, ...] + [b, ...] open or close?
What about [a] + [b, ...]? And so on.

With the current semantics of comprehensions, they
are also unnecessary. The above can be written as
    [ for x in a {x}, for x in b {x} ].

Though more verbose, it is very clear here that
regardless of whether a and b are open or closed
the result is always closed.

With the query extension, this can also be written
more succinctly, like `[ a.[_], b.[_] ]` or perhaps
`[a.*, b.*]`, either case is clearer than using list
operators.

See Issue #165.

In order to move to being able to give backwards
compatiblity guarantees, we propose getting rid of list
addition and multiplication. An automatic rewriter could
rewrite the old use using `list.Repeat` and `list.Concat`,
the latter of which could refer to the spec to indicate
its equivalence to using comprehensions or, later, queries.

Change-Id: I374bfd59775d66d3da9feb28e1940f8bd3c255e8
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/8063
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Paul Jolly <paul@myitcv.org.uk>
Reviewed-by: Jonathan Amsterdam <jba@google.com>