Unverified Commit 8437d13b authored by Robert Hensing's avatar Robert Hensing Committed by GitHub
Browse files

Merge pull request #296272 from hsjobeki/lib/foldl-prime 

lib.foldl': avoid unnecessary function call
parents 39cfb51a c8885b86

lib/lists.nix

+10 −4
Original line number Diff line number Diff line
@@ -228,7 +228,15 @@ rec { 


    `acc`



    : The initial accumulator value

    : The initial accumulator value.



      The accumulator value is evaluated in any case before the first iteration starts.



      To avoid evaluation even before the `list` argument is given an eta expansion can be used:



      ```nix

      list: lib.foldl' op acc list

      ```



    `list`
@@ -254,13 +262,11 @@ rec { 
  foldl' =

    op:

    acc:

    list:



    # The builtin `foldl'` is a bit lazier than one might expect.

    # See https://github.com/NixOS/nix/pull/7158.

    # In particular, the initial accumulator value is not forced before the first iteration starts.

    builtins.seq acc

      (builtins.foldl' op acc list);

      (builtins.foldl' op acc);



  /**

    Map with index starting from 0