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reword and reformat description of builtins.import

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Valentin Gagarin 2023-10-07 02:53:41 +02:00
parent a7ba8c3f4a
commit 6305801626
1 changed files with 55 additions and 46 deletions
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101
src/libexpr/primops.cc
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@ -258,62 +258,71 @@ static RegisterPrimOp primop_import({
.args = {"path"}, .args = {"path"},
// TODO turn "normal path values" into link below // TODO turn "normal path values" into link below
.doc = R"( .doc = R"(
Load, parse and return the Nix expression in the file *path*. Load, parse, and return the Nix expression in the file *path*.
The *path* argument must meet the same criteria as an [interpolated expression](@docroot@/language/string-interpolation.md#interpolated-expression).
If *path* is a directory, the file `default.nix` in that directory
is loaded.
Evaluation aborts if the file doesn’t exist or contains
an incorrect Nix expression. `import` implements Nix’s module
system: you can put any Nix expression (such as a set or a
function) in a separate file, and use it from Nix expressions in
other files.
> **Note** > **Note**
> >
> Unlike some languages, `import` is a regular function in Nix. > Unlike some languages, `import` is a regular function in Nix.
> Paths using the angle bracket syntax (e.g., `import` *\<foo\>*)
> are normal [path values](@docroot@/language/values.md#type-path).
A Nix expression loaded by `import` must not contain any *free The *path* argument must meet the same criteria as an [interpolated expression](@docroot@/language/string-interpolation.md#interpolated-expression).
variables* (identifiers that are not defined in the Nix expression
itself and are not built-in). Therefore, it cannot refer to
variables that are in scope at the call site. For instance, if you
have a calling expression
```nix If *path* is a directory, the file `default.nix` in that directory is used if it exists.
rec {
x = 123;
y = import ./foo.nix;
}
```
then the following `foo.nix` will give an error: > **Example**
>
> ```console
> $ echo 123 > default.nix
> ```
>
> Import `default.nix` from the current directory.
>
> ```nix
> import ./.
> ```
>
> 123
```nix Evaluation aborts if the file doesn’t exist or contains an invalid Nix expression.
x + 456
```
since `x` is not in scope in `foo.nix`. If you want `x` to be A Nix expression loaded by `import` must not contain any *free variables*, that is, identifiers that are not defined in the Nix expression itself and are not built-in.
available in `foo.nix`, you should pass it as a function argument: Therefore, it cannot refer to variables that are in scope at the call site.
```nix > **Example**
rec { >
x = 123; > If you have a calling expression
y = import ./foo.nix x; >
} > ```nix
``` > rec {
> x = 123;
and > y = import ./foo.nix;
> }
```nix > ```
x: x + 456 >
``` > then the following `foo.nix` will give an error:
>
(The function argument doesn’t have to be called `x` in `foo.nix`; > ```nix
any name would work.) > # foo.nix
> x + 456
> ```
>
> since `x` is not in scope in `foo.nix`.
> If you want `x` to be available in `foo.nix`, pass it as a function argument:
>
> ```nix
> rec {
> x = 123;
> y = import ./foo.nix x;
> }
> ```
>
> and
>
> ```nix
> # foo.nix
> x: x + 456
> ```
>
> The function argument doesn’t have to be called `x` in `foo.nix`; any name would work.
)", )",
.fun = [](EvalState & state, const PosIdx pos, Value * * args, Value & v) .fun = [](EvalState & state, const PosIdx pos, Value * * args, Value & v)
{ {