diff options
author | danbst <abcz2.uprola@gmail.com> | 2019-07-14 13:17:49 +0300 |
---|---|---|
committer | danbst <abcz2.uprola@gmail.com> | 2019-07-14 13:29:58 +0300 |
commit | 69920dafbffcd757acff23f659263ec4b952a017 (patch) | |
tree | 4390925c6087d284c11183193044835152f6cea5 /lib/lists.nix | |
parent | 696767a9c9dc4b6b5066a3172c89138c0bb6e40d (diff) |
lib: introduce `foreach` = flip map
The main purpose is to bring attention to `flip map`, which improves
code readablity. It is useful when ad-hoc anonymous function
grows two or more lines in `map` application:
```
map (lcfg:
let port = lcfg.port;
portStr = if port != defaultPort then ":${toString port}" else "";
scheme = if cfg.enableSSL then "https" else "http";
in "${scheme}://cfg.hostName${portStr}"
) (getListen cfg);
```
Compare this to `foreach`-style:
```
foreach (getListen cfg) (lcfg:
let port = lcfg.port;
portStr = if port != defaultPort then ":${toString port}" else "";
scheme = if cfg.enableSSL then "https" else "http";
in "${scheme}://cfg.hostName${portStr}"
);
```
This is similar to Haskell's `for` (http://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Traversable.html#v:for)
Diffstat (limited to 'lib/lists.nix')
-rw-r--r-- | lib/lists.nix | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/lib/lists.nix b/lib/lists.nix index 30d87ece6641..f9953720ee10 100644 --- a/lib/lists.nix +++ b/lib/lists.nix @@ -21,6 +21,19 @@ rec { */ singleton = x: [x]; + /* Apply the function to each element in the list. Same as `map`, but arguments + flipped. + + Type: foreach :: [a] -> (a -> b) -> [b] + + Example: + foreach [ 1 2 ] (x: + toString x + ) + => [ "1" "2" ] + */ + foreach = xs: f: map f xs; + /* “right fold” a binary function `op` between successive elements of `list` with `nul' as the starting value, i.e., `foldr op nul [x_1 x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))`. |