42 lines
1.2 KiB
Nix
42 lines
1.2 KiB
Nix
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# Utility functions.
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rec {
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# "Fold" a binary function `op' between successive elements of
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# `list' with `nul' as the starting value, i.e., `fold op nul [x_1
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# x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))'. (This is
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# Haskell's foldr).
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fold = op: nul: list:
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if list == []
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then nul
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else op (builtins.head list) (fold op nul (builtins.tail list));
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# Concatenate a list of strings.
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concatStrings =
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fold (x: y: x + y) "";
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# Flatten the argument into a single list; that is, nested lists are
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# spliced into the top-level lists. E.g., `flatten [1 [2 [3] 4] 5]
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# == [1 2 3 4 5]' and `flatten 1 == [1]'.
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flatten = x:
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if builtins.isList x
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then fold (x: y: (flatten x) ++ y) [] x
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else [x];
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# Return an attribute from nested attribute sets. For instance ["x"
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# "y"] applied to some set e returns e.x.y, if it exists. The
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# default value is returned otherwise.
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getAttr = attrPath: default: e:
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let {
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attr = builtins.head attrPath;
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body =
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if attrPath == [] then e
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else if builtins ? hasAttr && builtins.hasAttr attr e
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then getAttr (builtins.tail attrPath) default (builtins.getAttr attr e)
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else default;
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};
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}
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