diff options
Diffstat (limited to 'doc/manual/src/language')
-rw-r--r-- | doc/manual/src/language/builtin-constants.md | 31 | ||||
-rw-r--r-- | doc/manual/src/language/builtins-prefix.md | 20 | ||||
-rw-r--r-- | doc/manual/src/language/operators.md | 2 | ||||
-rw-r--r-- | doc/manual/src/language/values.md | 8 |
4 files changed, 32 insertions, 29 deletions
diff --git a/doc/manual/src/language/builtin-constants.md b/doc/manual/src/language/builtin-constants.md index 78d066a82..c6bc9b74c 100644 --- a/doc/manual/src/language/builtin-constants.md +++ b/doc/manual/src/language/builtin-constants.md @@ -1,20 +1,19 @@ # Built-in Constants -Here are the constants built into the Nix expression evaluator: +These constants are built into the Nix language evaluator: - - `builtins`\ - The set `builtins` contains all the built-in functions and values. - You can use `builtins` to test for the availability of features in - the Nix installation, e.g., - - ```nix - if builtins ? getEnv then builtins.getEnv "PATH" else "" - ``` - - This allows a Nix expression to fall back gracefully on older Nix - installations that don’t have the desired built-in function. +- [`builtins`]{#builtins-builtins} (attribute set) - - [`builtins.currentSystem`]{#builtins-currentSystem}\ - The built-in value `currentSystem` evaluates to the Nix platform - identifier for the Nix installation on which the expression is being - evaluated, such as `"i686-linux"` or `"x86_64-darwin"`. + Contains all the [built-in functions](./builtins.md) and values, in order to avoid polluting the global scope. + + Since built-in functions were added over time, [testing for attributes](./operators.md#has-attribute) in `builtins` can be used for graceful fallback on older Nix installations: + + ```nix + if builtins ? getEnv then builtins.getEnv "PATH" else "" + ``` + +- [`builtins.currentSystem`]{#builtins-currentSystem} (string) + + The built-in value `currentSystem` evaluates to the Nix platform + identifier for the Nix installation on which the expression is being + evaluated, such as `"i686-linux"` or `"x86_64-darwin"`. diff --git a/doc/manual/src/language/builtins-prefix.md b/doc/manual/src/language/builtins-prefix.md index c631a8453..35e3dccc3 100644 --- a/doc/manual/src/language/builtins-prefix.md +++ b/doc/manual/src/language/builtins-prefix.md @@ -1,16 +1,16 @@ # Built-in Functions -This section lists the functions built into the Nix expression -evaluator. (The built-in function `derivation` is discussed above.) -Some built-ins, such as `derivation`, are always in scope of every Nix -expression; you can just access them right away. But to prevent -polluting the namespace too much, most built-ins are not in -scope. Instead, you can access them through the `builtins` built-in -value, which is a set that contains all built-in functions and values. -For instance, `derivation` is also available as `builtins.derivation`. +This section lists the functions built into the Nix language evaluator. +All built-in functions are available through the global [`builtins`](./builtin-constants.md#builtins-builtins) constant. + +For convenience, some built-ins are can be accessed directly: + +- [`derivation`](#builtins-derivation) +- [`import`](#builtins-import) +- [`abort`](#builtins-abort) +- [`throw`](#builtins-throw) <dl> - <dt><code>derivation <var>attrs</var></code>; - <code>builtins.derivation <var>attrs</var></code></dt> + <dt id="builtins-derivation"><a href="#builtins-derivation"><code>derivation <var>attrs</var></code></a></dt> <dd><p><var>derivation</var> is described in <a href="derivations.md">its own section</a>.</p></dd> diff --git a/doc/manual/src/language/operators.md b/doc/manual/src/language/operators.md index a07d976ad..3e929724d 100644 --- a/doc/manual/src/language/operators.md +++ b/doc/manual/src/language/operators.md @@ -36,7 +36,7 @@ ## Attribute selection Select the attribute denoted by attribute path *attrpath* from [attribute set] *attrset*. -If the attribute doesn’t exist, return *value* if provided, otherwise abort evaluation. +If the attribute doesn’t exist, return the *expr* after `or` if provided, otherwise abort evaluation. <!-- FIXME: the following should to into its own language syntax section, but that needs more work to fit in well --> diff --git a/doc/manual/src/language/values.md b/doc/manual/src/language/values.md index c85124278..9d0301753 100644 --- a/doc/manual/src/language/values.md +++ b/doc/manual/src/language/values.md @@ -190,13 +190,17 @@ instance, ``` evaluates to `"Foo"`. It is possible to provide a default value in an -attribute selection using the `or` keyword. For example, +attribute selection using the `or` keyword: ```nix { a = "Foo"; b = "Bar"; }.c or "Xyzzy" ``` -will evaluate to `"Xyzzy"` because there is no `c` attribute in the set. +```nix +{ a = "Foo"; b = "Bar"; }.c.d.e.f.g or "Xyzzy" +``` + +will both evaluate to `"Xyzzy"` because there is no `c` attribute in the set. You can use arbitrary double-quoted strings as attribute names: |