`pipe` is a useful operator for creating pipelines of functions.
It works around the usual problem of e.g. string operations becoming
deeply nested functions.
In principle, there are four different ways this function could be
written:
pipe val [ f1 .. fn ]
pipe val [ fn .. f1 ]
compose [ f1 .. fn ] val
compose [ fn .. f1 ] val
The third and fourth form mirror composition of functions, they would
be the same as e.g. `(f1 << f2 << f3 .. << fn) val`.
However, it is not clear which direction the list should have (as one
can see in the second form, which is the most absurd.
In order not to confuse users, we decide for the most “intuitive”
form, which mirrors the way unix pipes work (thus the name `pipe`).
The flow of data goes from left to right.
Co-Authored-By: Silvan Mosberger <infinisil@icloud.com>
toPath has confusing semantics and is never necessary; it can always
either just be omitted or replaced by pre-concatenating `/.`. It has
been marked as "!!! obsolete?" for more than 10 years in a C++
comment, hopefully removing it will let us properly deprecate and,
eventually, remove it.
So far, `mkValueString` defaulted to `toString`,
which is a bad match for most configuration file formats,
especially because how booleans are formatted.
This also improves error messages for unsupported types.
Add a test to codify the formatting.
This means the generation of values can now be influenced, even down from e.g.
an INI generator.
Breaks the interface of `mkKeyValueDefault` to match its interface to other
generator functions. It might me sensible to rename `mkKeyValue` and
`mkKeyValueSet` to conform to the `toX`-style of generator functions.
With `builtins.functionArgs` we can get some information if the first argument
is an attrset and whether the contained fields have default values. Encode that
into the pretty-printed lambda.
