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init: lib.foldlAttrs

- provide comprehensive example
- add unit test
This commit is contained in:
hsjobeki 2023-02-28 11:04:19 +01:00
parent 624432c25b
commit 15a8d05ba5
3 changed files with 92 additions and 1 deletions

View file

@ -333,6 +333,66 @@ rec {
) (attrNames set)
);
/*
Like builtins.foldl' but for attribute sets.
Iterates over every name-value pair in the given attribute set.
The result of the callback function is often called `acc` for accumulator. It is passed between callbacks from left to right and the final `acc` is the return value of `foldlAttrs`.
Attention:
There is a completely different function
`lib.foldAttrs`
which has nothing to do with this function, despite the similar name.
Example:
foldlAttrs
(acc: name: value: {
sum = acc.sum + value;
names = acc.names ++ [name];
})
{ sum = 0; names = []; }
{
foo = 1;
bar = 10;
}
->
{
sum = 11;
names = ["bar" "foo"];
}
foldlAttrs
(throw "function not needed")
123
{};
->
123
foldlAttrs
(_: _: v: v)
(throw "initial accumulator not needed")
{ z = 3; a = 2; };
->
3
The accumulator doesn't have to be an attrset.
It can be as simple as a number or string.
foldlAttrs
(acc: _: v: acc * 10 + v)
1
{ z = 1; a = 2; };
->
121
Type:
foldlAttrs :: ( a -> String -> b -> a ) -> a -> { ... :: b } -> a
*/
foldlAttrs = f: init: set:
foldl'
(acc: name: f acc name set.${name})
init
(attrNames set);
/* Apply fold functions to values grouped by key.
Example:

View file

@ -78,7 +78,7 @@ let
composeManyExtensions makeExtensible makeExtensibleWithCustomName;
inherit (self.attrsets) attrByPath hasAttrByPath setAttrByPath
getAttrFromPath attrVals attrValues getAttrs catAttrs filterAttrs
filterAttrsRecursive foldAttrs collect nameValuePair mapAttrs
filterAttrsRecursive foldlAttrs foldAttrs collect nameValuePair mapAttrs
mapAttrs' mapAttrsToList concatMapAttrs mapAttrsRecursive mapAttrsRecursiveCond
genAttrs isDerivation toDerivation optionalAttrs
zipAttrsWithNames zipAttrsWith zipAttrs recursiveUpdateUntil

View file

@ -533,6 +533,37 @@ runTests {
};
};
# code from example
testFoldlAttrs = {
expr = {
example = foldlAttrs
(acc: name: value: {
sum = acc.sum + value;
names = acc.names ++ [ name ];
})
{ sum = 0; names = [ ]; }
{
foo = 1;
bar = 10;
};
# should just return the initial value
emptySet = foldlAttrs (throw "function not needed") 123 { };
# should just evaluate to the last value
accNotNeeded = foldlAttrs (_acc: _name: v: v) (throw "accumulator not needed") { z = 3; a = 2; };
# the accumulator doesnt have to be an attrset it can be as trivial as being just a number or string
trivialAcc = foldlAttrs (acc: _name: v: acc * 10 + v) 1 { z = 1; a = 2; };
};
expected = {
example = {
sum = 11;
names = [ "bar" "foo" ];
};
emptySet = 123;
accNotNeeded = 3;
trivialAcc = 121;
};
};
# code from the example
testRecursiveUpdateUntil = {
expr = recursiveUpdateUntil (path: l: r: path == ["foo"]) {