diff --git a/pkgs/lib/lists.nix b/pkgs/lib/lists.nix index f5845c32ee9..d6ab9cb88a7 100644 --- a/pkgs/lib/lists.nix +++ b/pkgs/lib/lists.nix @@ -1,7 +1,7 @@ # General list operations. rec { - inherit (builtins) head tail length isList; + inherit (builtins) elemAt head tail length isList add sub lessThan; # Create a list consisting of a single element. `singleton x' is @@ -14,20 +14,46 @@ rec { # `list' with `nul' as the starting value, i.e., `fold op nul [x_1 # x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))'. (This is # Haskell's foldr). - fold = op: nul: list: - if list == [] - then nul - else op (head list) (fold op nul (tail list)); + fold = + if builtins ? elemAt + then op: nul: list: + let + len = length list; + fold' = n: + if n == len + then nul + else op (elemAt list n) (fold' (add n 1)); + in fold' 0 + else op: nul: + let fold' = list: + if list == [] + then nul + else op (head list) (fold' (tail list)); + in fold'; # Left fold: `fold op nul [x_1 x_2 ... x_n] == op (... (op (op nul # x_1) x_2) ... x_n)'. - foldl = op: nul: list: - if list == [] - then nul - else foldl op (op nul (head list)) (tail list); + foldl = + if builtins ? elemAt + then op: nul: list: + let + len = length list; + foldl' = n: + if n == minus1 + then nul + else op (foldl' (sub n 1)) (elemAt list n); + in foldl' (sub (length list) 1) + else op: + let foldl' = nul: list: + if list == [] + then nul + else foldl' (op nul (head list)) (tail list); + in foldl'; + + minus1 = sub 0 1; + - # map with index: `imap (i: v: "${v}-${toString i}") ["a" "b"] == # ["a-1" "b-2"]' imap = f: list: @@ -92,18 +118,12 @@ rec { # Return true iff function `pred' returns true for at least element # of `list'. - any = pred: list: - if list == [] then false - else if pred (head list) then true - else any pred (tail list); + any = pred: fold (x: y: if pred x then true else y) false; # Return true iff function `pred' returns true for all elements of # `list'. - all = pred: list: - if list == [] then true - else if pred (head list) then all pred (tail list) - else false; + all = pred: fold (x: y: if pred x then y else false) true; # Return true if each element of a list is equal, false otherwise.