attrByPath :: [String] -> Any -> AttrSet -> Any Return an attribute from within nested attribute sets. attrPath A list of strings representing the path through the nested attribute set set. default Default value if attrPath does not resolve to an existing value. set The nested attributeset to select values from. 3 ]]> 0 ]]>

hasAttrByPath :: [String] -> AttrSet -> Bool Determine if an attribute exists within a nested attribute set. attrPath A list of strings representing the path through the nested attribute set set. set The nested attributeset to check. true ]]>

setAttrByPath :: [String] -> Any -> AttrSet Create a new attribute set with value set at the nested attribute location specified in attrPath. attrPath A list of strings representing the path through the nested attribute set. value The value to set at the location described by attrPath. { a = { b = 3; }; } ]]>

getAttrFromPath :: [String] -> AttrSet -> Value Like [](#function-library-lib.attrsets.attrByPath) except without a default, and it will throw if the value doesn't exist. attrPath A list of strings representing the path through the nested attribute set set. set The nested attribute set to find the value in. 3 ]]> error: cannot find attribute `x.y' ]]>

attrVals :: [String] -> AttrSet -> [Any] Return the specified attributes from a set. All values must exist. nameList The list of attributes to fetch from set. Each attribute name must exist on the attrbitue set. set The set to get attribute values from. [ 1 2 3 ] ]]>

attrValues :: AttrSet -> [Any] Get all the attribute values from an attribute set. Provides a backwards-compatible interface of builtins.attrValues for Nix version older than 1.8. attrs The attribute set. [ 1 2 3 ] ]]>

catAttrs :: String -> [AttrSet] -> [Any] Collect each attribute named `attr' from the list of attribute sets, sets. Sets that don't contain the named attribute are ignored. Provides a backwards-compatible interface of builtins.catAttrs for Nix version older than 1.9. attr Attribute name to select from each attribute set in sets. sets The list of attribute sets to select attr from. Attribute sets which don't have the attribute are ignored. [ 1 2 ] ]]>

filterAttrs :: (String -> Any -> Bool) -> AttrSet -> AttrSet Filter an attribute set by removing all attributes for which the given predicate return false. pred String -> Any -> Bool Predicate which returns true to include an attribute, or returns false to exclude it. name The attribute's name value The attribute's value Returns true to include the attribute, false to exclude the attribute. set The attribute set to filter { foo = 1; } ]]>

filterAttrsRecursive :: (String -> Any -> Bool) -> AttrSet -> AttrSet Filter an attribute set recursively by removing all attributes for which the given predicate return false. pred String -> Any -> Bool Predicate which returns true to include an attribute, or returns false to exclude it. name The attribute's name value The attribute's value Returns true to include the attribute, false to exclude the attribute. set The attribute set to filter { levelA = { example = "hi"; levelB = { hello = "there"; this-one-is-present = { }; }; }; } ]]>

foldAttrs :: (Any -> Any -> Any) -> Any -> [AttrSets] -> Any Apply fold function to values grouped by key. op Any -> Any -> Any Given a value val and a collector col, combine the two. val An attribute's value col The result of previous op calls with other values and nul. nul The null-value, the starting value. list_of_attrs A list of attribute sets to fold together by key. { a = [ 2 3 ]; b = [ 7 6 ]; } ]]>

collect :: (Any -> Bool) -> AttrSet -> [Any] Recursively collect sets that verify a given predicate named pred from the set attrs. The recursion stops when pred returns true. pred Any -> Bool Given an attribute's value, determine if recursion should stop. value The attribute set value. attrs The attribute set to recursively collect. [["b"] [1]] ]]> [{ outPath = "a/"; } { outPath = "b/"; }] ]]>

nameValuePair :: String -> Any -> AttrSet Utility function that creates a {name, value} pair as expected by builtins.listToAttrs. name The attribute name. value The attribute value. { name = "some"; value = 6; } ]]>

Apply a function to each element in an attribute set, creating a new attribute set. Provides a backwards-compatible interface of builtins.mapAttrs for Nix version older than 2.1. fn String -> Any -> Any Given an attribute's name and value, return a new value. name The name of the attribute. value The attribute's value. { x = "x-foo"; y = "y-bar"; } ]]>

mapAttrs' :: (String -> Any -> { name = String; value = Any }) -> AttrSet -> AttrSet Like mapAttrs, but allows the name of each attribute to be changed in addition to the value. The applied function should return both the new name and value as a nameValuePair. fn String -> Any -> { name = String; value = Any } Given an attribute's name and value, return a new name value pair. name The name of the attribute. value The attribute's value. set The attribute set to map over. { foo_x = "bar-a"; foo_y = "bar-b"; } ]]>

mapAttrsToList :: (String -> Any -> Any) -> AttrSet -> [Any] Call fn for each attribute in the given set and return the result in a list. fn String -> Any -> Any Given an attribute's name and value, return a new value. name The name of the attribute. value The attribute's value. set The attribute set to map over. [ "x=a" "y=b" ] ]]>

mapAttrsRecursive :: ([String] > Any -> Any) -> AttrSet -> AttrSet Like mapAttrs, except that it recursively applies itself to attribute sets. Also, the first argument of the argument function is a list of the names of the containing attributes. f [ String ] -> Any -> Any Given a list of attribute names and value, return a new value. name_path The list of attribute names to this value. For example, the name_path for the example string in the attribute set { foo = { bar = "example"; }; } is [ "foo" "bar" ]. value The attribute's value. set The attribute set to recursively map over. { n = { a = "n-a-A"; m = { b = "n-m-b-B"; c = "n-m-c-C"; }; }; d = "d-D"; } ]]>

mapAttrsRecursiveCond :: (AttrSet -> Bool) -> ([ String ] -> Any -> Any) -> AttrSet -> AttrSet Like mapAttrsRecursive, but it takes an additional predicate function that tells it whether to recursive into an attribute set. If it returns false, mapAttrsRecursiveCond does not recurse, but does apply the map function. It is returns true, it does recurse, and does not apply the map function. cond (AttrSet -> Bool) Determine if mapAttrsRecursive should recurse deeper in to the attribute set. attributeset An attribute set. f [ String ] -> Any -> Any Given a list of attribute names and value, return a new value. name_path The list of attribute names to this value. For example, the name_path for the example string in the attribute set { foo = { bar = "example"; }; } is [ "foo" "bar" ]. value The attribute's value. set The attribute set to recursively map over. { dorecur = { hello = "\"there\""; recurse = "true"; }; dontrecur = "{\"converted-to\":\"json\"}"; } ]]>

genAttrs :: [ String ] -> (String -> Any) -> AttrSet Generate an attribute set by mapping a function over a list of attribute names. names Names of values in the resulting attribute set. f String -> Any Takes the name of the attribute and return the attribute's value. name The name of the attribute to generate a value for. { foo = "x_foo"; bar = "x_bar"; } ]]>

isDerivation :: Any -> Bool Check whether the argument is a derivation. Any set with { type = "derivation"; } counts as a derivation. value The value which is possibly a derivation. {}).ruby => true ]]> false ]]>

toDerivation :: Path -> Derivation Converts a store path to a fake derivation. path A store path to convert to a derivation.

optionalAttrs :: Bool -> AttrSet Conditionally return an attribute set or an empty attribute set. cond Condition under which the as attribute set is returned. as The attribute set to return if cond is true. { my = "set"; } ]]> { } ]]>

zipAttrsWithNames :: [ String ] -> (String -> [ Any ] -> Any) -> [ AttrSet ] -> AttrSet Merge sets of attributes and use the function f to merge attribute values where the attribute name is in names. names A list of attribute names to zip. f (String -> [ Any ] -> Any Accepts an attribute name, all the values, and returns a combined value. name The name of the attribute each value came from. vs A list of values collected from the list of attribute sets. sets A list of attribute sets to zip together. { a = "a 11"; b = "b 101"; } ]]>

zipAttrsWith :: (String -> [ Any ] -> Any) -> [ AttrSet ] -> AttrSet Merge sets of attributes and use the function f to merge attribute values. Similar to where all key names are passed for names. f (String -> [ Any ] -> Any Accepts an attribute name, all the values, and returns a combined value. name The name of the attribute each value came from. vs A list of values collected from the list of attribute sets. sets A list of attribute sets to zip together. { a = "a 11"; b = "b 101"; c = "c 1001"; } ]]>

zipAttrsWith :: [ AttrSet ] -> AttrSet Merge sets of attributes and combine each attribute value in to a list. Similar to [](#function-library-lib.attrsets.zipAttrsWith) where the merge function returns a list of all values. sets A list of attribute sets to zip together. { a = [ 1 10 ]; b = [ 1 100 ]; c = [ 1 1000 ]; } ]]>

recursiveUpdateUntil :: ( [ String ] -> AttrSet -> AttrSet -> Bool ) -> AttrSet -> AttrSet -> AttrSet Does the same as the update operator // except that attributes are merged until the given predicate is verified. The predicate should accept 3 arguments which are the path to reach the attribute, a part of the first attribute set and a part of the second attribute set. When the predicate is verified, the value of the first attribute set is replaced by the value of the second attribute set. pred [ String ] -> AttrSet -> AttrSet -> Bool path The path to the values in the left and right hand sides. l The left hand side value. r The right hand side value. lhs The left hand attribute set of the merge. rhs The right hand attribute set of the merge. { foo.bar = 1; # 'foo.*' from the second set foo.quz = 2; # bar = 3; # 'bar' from the first set baz = 4; # 'baz' from the second set } ]]>

recursiveUpdate :: AttrSet -> AttrSet -> AttrSet A recursive variant of the update operator //. The recursion stops when one of the attribute values is not an attribute set, in which case the right hand side value takes precedence over the left hand side value. lhs The left hand attribute set of the merge. rhs The right hand attribute set of the merge. { boot.loader.grub.enable = true; boot.loader.grub.device = ""; } ]]>

recurseIntoAttrs :: AttrSet -> AttrSet Make various Nix tools consider the contents of the resulting attribute set when looking for what to build, find, etc. This function only affects a single attribute set; it does not apply itself recursively for nested attribute sets. attrs An attribute set to scan for derivations. {} }: { myTools = pkgs.lib.recurseIntoAttrs { inherit (pkgs) hello figlet; }; } ]]>

cartesianProductOfSets :: AttrSet -> [ AttrSet ] Return the cartesian product of attribute set value combinations. set An attribute set with attributes that carry lists of values. [ { a = 1; b = 10; } { a = 1; b = 20; } { a = 2; b = 10; } { a = 2; b = 20; } ] ]]>