Nix Language Quirks: Difference between revisions
Add quirk related to builtins.toString handling of true vs false |
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{{merge|Nix | {{merge|Nix (language)}} | ||
== <code>with</code> and <code>let</code> == | == <code>with</code> and <code>let</code> == | ||
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Note, that it isn't equivalent to <code>with rec { x = 1; y = x + 1; body = y; }; body</code> because of mentioned <code>with</code> and <code>let</code> quirk, but is same as <code>rec { x = 1; y = x + 1; body = y; }.body</code> | Note, that it isn't equivalent to <code>with rec { x = 1; y = x + 1; body = y; }; body</code> because of mentioned <code>with</code> and <code>let</code> quirk, but is same as <code>rec { x = 1; y = x + 1; body = y; }.body</code> | ||
== Default values are not bound in @ syntax == | == Default values are not bound in <code>@</code> syntax == | ||
Destructured arguments can have default values, but those default values are part of the full function argument. | Destructured arguments can have default values, but those default values are part of the full function argument. | ||
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consider the use of <code>import</code> here similar to using <code>qualified import ...</code> in Haskell or <code>import ...</code> in Python. Another (discouraged and increasingly uncommon) way of importing is [https://nix.dev/manual/nix/2.24/language/syntax#with-expressions <code>with import ...;</code>], which corresponds to Python <code>from ... import *</code>. This use of <code>with</code> imports everything from the target into scope, which has numerous potential gotchas and problems, and so using [https://nix.dev/guides/best-practices#with-scopes <code>inherit</code>] instead is encouraged and preferred. | consider the use of <code>import</code> here similar to using <code>qualified import ...</code> in Haskell or <code>import ...</code> in Python. Another (discouraged and increasingly uncommon) way of importing is [https://nix.dev/manual/nix/2.24/language/syntax#with-expressions <code>with import ...;</code>], which corresponds to Python <code>from ... import *</code>. This use of <code>with</code> imports everything from the target into scope, which has numerous potential gotchas and problems, and so using [https://nix.dev/guides/best-practices#with-scopes <code>inherit</code>] instead is encouraged and preferred. | ||
== builtins.replaceStrings key match on "" == | == <code>builtins.replaceStrings</code> key match on "" == | ||
Syntax: | Syntax: | ||
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There is an example in <code>coq</code> package code [https://github.com/NixOS/nixpkgs/blob/5185539c51ba658e70b29e01c0c320a85f4e2098/pkgs/build-support/coq/extra-lib.nix#L98 here] where someone used this behavior to build a reusable function <code>switch</code>. | There is an example in <code>coq</code> package code [https://github.com/NixOS/nixpkgs/blob/5185539c51ba658e70b29e01c0c320a85f4e2098/pkgs/build-support/coq/extra-lib.nix#L98 here] where someone used this behavior to build a reusable function <code>switch</code>. | ||
== builtins.toString true and false | == <code>builtins.toString</code> handling of <code>true</code> and <code>false</code> is inconsistent == | ||
<syntaxHighlight lang=nix> | <syntaxHighlight lang=nix> | ||
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nix-repl> let code = "(x: x) ''id function was called''"; in import (builtins.toFile "eval" code) | nix-repl> let code = "(x: x) ''id function was called''"; in import (builtins.toFile "eval" code) | ||
"id function was called"</syntaxHighlight> | "id function was called"</syntaxHighlight> | ||
= Resources = | |||
* [https://md.darmstadt.ccc.de/xtNP7JuIQ5iNW1FjuhUccw# A separately maintained list of Nix language quirks] | |||
[[Category:Nix Language]] | [[Category:Nix Language]] | ||