# 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 []; }