diff options
Diffstat (limited to 'lib/lists.nix')
| -rw-r--r-- | lib/lists.nix | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/lib/lists.nix b/lib/lists.nix index eb7e6baf5ed..d0b09539bf6 100644 --- a/lib/lists.nix +++ b/lib/lists.nix @@ -118,6 +118,11 @@ in rec { all = pred: fold (x: y: if pred x then y else false) true; + # Count how many times function `pred' returns true for the elements + # of `list'. + count = pred: fold (x: c: if pred x then inc c else c) 0; + + # Return a singleton list or an empty list, depending on a boolean # value. Useful when building lists with optional elements # (e.g. `++ optional (system == "i686-linux") flashplayer'). |