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# Operations on attribute sets.
with {
inherit (builtins) head tail;
inherit (import ./default.nix) fold;
inherit (import ./strings.nix) concatStringsSep;
};
rec {
inherit (builtins) attrNames listToAttrs hasAttr isAttrs;
/* Return an attribute from nested attribute sets. For instance
["x" "y"] applied to some set e returns e.x.y, if it exists. The
default value is returned otherwise. !!! there is also
builtins.getAttr (is there a better name for this function?)
*/
getAttr = attrPath: default: e:
let attr = head attrPath;
in
if attrPath == [] then e
else if builtins ? hasAttr && hasAttr attr e
then getAttr (tail attrPath) default (builtins.getAttr attr e)
else default;
getAttrFromPath = attrPath: set:
let errorMsg = "cannot find attribute `" + concatStringsSep "." attrPath + "'";
in getAttr attrPath (abort errorMsg) set;
/* Return the specified attributes from a set.
Example:
attrVals ["a" "b" "c"] as
=> [as.a as.b as.c]
*/
attrVals = nameList: set:
map (x: builtins.getAttr x set) nameList;
/* Return the values of all attributes in the given set, sorted by
attribute name.
Example:
attrValues {c = 3; a = 1; b = 2;}
=> [1 2 3]
*/
attrValues = attrs: attrVals (attrNames attrs) attrs;
/* Collect each attribute named `attr' from a list of attribute
sets. Sets that don't contain the named attribute are ignored.
Example:
catAttrs "a" [{a = 1;} {b = 0;} {a = 2;}]
=> [1 2]
*/
catAttrs = attr: l: fold (s: l: if hasAttr attr s then [(builtins.getAttr attr s)] ++ l else l) [] l;
/* Utility function that creates a {name, value} pair as expected by
builtins.listToAttrs. */
nameValuePair = name: value: { inherit name value; };
/* Apply a function to each element in an attribute set. The
function takes two arguments --- the attribute name and its value
--- and returns the new value for the attribute. The result is a
new attribute set.
Example:
mapAttrs (name: value: name + "-" + value)
{x = "foo"; y = "bar";}
=> {x = "x-foo"; y = "y-bar";}
*/
mapAttrs = f: set:
listToAttrs (map (attr: nameValuePair attr (f attr (builtins.getAttr attr set))) (attrNames set));
/* Like `mapAttrs', except that it recursively applies itself to
values that attribute sets. Also, the first argument is a *list*
of the names of the containing attributes.
Example:
mapAttrsRecursive (path: value: concatStringsSep "-" (path ++ [value]))
{ n = { a = "A"; m = { b = "B"; c = "C"; }; }; d = "D"; }
=> { n = { a = "n-a-A"; m = { b = "n-m-b-B"; c = "n-m-c-C"; }; }; d = "d-D"; }
*/
mapAttrsRecursive =
let
recurse = path: f: set:
let
g =
name: value:
if isAttrs value
then recurse (path ++ [name]) f value
else f (path ++ [name]) value;
in mapAttrs g set;
in recurse [];
}
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