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Diffstat (limited to 'doc/manual/src/language/operators.md')
| -rw-r--r-- | doc/manual/src/language/operators.md | 32 |
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diff --git a/doc/manual/src/language/operators.md b/doc/manual/src/language/operators.md index 6dcdc6eb0..2d4707814 100644 --- a/doc/manual/src/language/operators.md +++ b/doc/manual/src/language/operators.md @@ -26,6 +26,8 @@ | Logical conjunction (`AND`) | *bool* `&&` *bool* | left | 12 | | Logical disjunction (`OR`) | *bool* <code>\|\|</code> *bool* | left | 13 | | [Logical implication] | *bool* `->` *bool* | none | 14 | +| \[Experimental\] [Function piping] | *expr* |> *func* | left | 15 | +| \[Experimental\] [Function piping] | *expr* <| *func* | right | 16 | [string]: ./values.md#type-string [path]: ./values.md#type-path @@ -215,3 +217,33 @@ nix-repl> let f = x: 1; s = { func = f; }; in [ (f == f) (s == s) ] Equivalent to `!`*b1* `||` *b2*. [Logical implication]: #logical-implication + +## \[Experimental\] Function piping + +*This language feature is still experimental and may change at any time. Enable `--extra-experimental-features pipe-operator` to use it.* + +Pipes are a dedicated operator for function application, but with reverse order and a lower binding strength. +This allows you to chain function calls together in way that is more natural to read and requires less parentheses. + +`a |> f b |> g` is equivalent to `g (f b a)`. +`g <| f b <| a` is equivalent to `g (f b a)`. + +Example code snippet: + +```nix +defaultPrefsFile = defaultPrefs + |> lib.mapAttrsToList ( + key: value: '' + // ${value.reason} + pref("${key}", ${builtins.toJSON value.value}); + '' + ) + |> lib.concatStringsSep "\n" + |> pkgs.writeText "nixos-default-prefs.js"; +``` + +Note how `mapAttrsToList` is called with two arguments (the lambda and `defaultPrefs`), +but moving the last argument in front of the rest improves the reading flow. +This is common for functions with long first argument, including all `map`-like functions. + +[Function piping]: #experimental-function-piping |