mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-11-15 18:56:16 +02:00
eb7d7780b1
This is needed to avoid this https://github.com/mesonbuild/meson/issues/13774 when we go back to making our subproject directory `src`.
235 lines
8.5 KiB
Markdown
235 lines
8.5 KiB
Markdown
# Operators
|
||
|
||
| Name | Syntax | Associativity | Precedence |
|
||
|----------------------------------------|--------------------------------------------|---------------|------------|
|
||
| [Attribute selection] | *attrset* `.` *attrpath* \[ `or` *expr* \] | none | 1 |
|
||
| [Function application] | *func* *expr* | left | 2 |
|
||
| [Arithmetic negation][arithmetic] | `-` *number* | none | 3 |
|
||
| [Has attribute] | *attrset* `?` *attrpath* | none | 4 |
|
||
| List concatenation | *list* `++` *list* | right | 5 |
|
||
| [Multiplication][arithmetic] | *number* `*` *number* | left | 6 |
|
||
| [Division][arithmetic] | *number* `/` *number* | left | 6 |
|
||
| [Subtraction][arithmetic] | *number* `-` *number* | left | 7 |
|
||
| [Addition][arithmetic] | *number* `+` *number* | left | 7 |
|
||
| [String concatenation] | *string* `+` *string* | left | 7 |
|
||
| [Path concatenation] | *path* `+` *path* | left | 7 |
|
||
| [Path and string concatenation] | *path* `+` *string* | left | 7 |
|
||
| [String and path concatenation] | *string* `+` *path* | left | 7 |
|
||
| Logical negation (`NOT`) | `!` *bool* | none | 8 |
|
||
| [Update] | *attrset* `//` *attrset* | right | 9 |
|
||
| [Less than][Comparison] | *expr* `<` *expr* | none | 10 |
|
||
| [Less than or equal to][Comparison] | *expr* `<=` *expr* | none | 10 |
|
||
| [Greater than][Comparison] | *expr* `>` *expr* | none | 10 |
|
||
| [Greater than or equal to][Comparison] | *expr* `>=` *expr* | none | 10 |
|
||
| [Equality] | *expr* `==` *expr* | none | 11 |
|
||
| Inequality | *expr* `!=` *expr* | none | 11 |
|
||
| Logical conjunction (`AND`) | *bool* `&&` *bool* | left | 12 |
|
||
| Logical disjunction (`OR`) | *bool* <code>\|\|</code> *bool* | left | 13 |
|
||
| [Logical implication] | *bool* `->` *bool* | right | 14 |
|
||
| [Pipe operator] (experimental) | *expr* `\|>` *func* | left | 15 |
|
||
| [Pipe operator] (experimental) | *func* `<\|` *expr* | right | 15 |
|
||
|
||
[string]: ./types.md#type-string
|
||
[path]: ./types.md#type-path
|
||
[number]: ./types.md#type-float
|
||
[list]: ./types.md#type-list
|
||
[attribute set]: ./types.md#type-attrs
|
||
|
||
<!-- TODO(@rhendric, #10970): ^ rationalize number -> int/float -->
|
||
|
||
## Attribute selection
|
||
|
||
> **Syntax**
|
||
>
|
||
> *attrset* `.` *attrpath* \[ `or` *expr* \]
|
||
|
||
Select the attribute denoted by attribute path *attrpath* from [attribute set] *attrset*.
|
||
If the attribute doesn’t exist, return the *expr* after `or` if provided, otherwise abort evaluation.
|
||
|
||
[Attribute selection]: #attribute-selection
|
||
|
||
## Function application
|
||
|
||
> **Syntax**
|
||
>
|
||
> *func* *expr*
|
||
|
||
Apply the callable value *func* to the argument *expr*. Note the absence of any visible operator symbol.
|
||
A callable value is either:
|
||
- a [user-defined function][function]
|
||
- a [built-in][builtins] function
|
||
- an attribute set with a [`__functor` attribute](./syntax.md#attr-__functor)
|
||
|
||
> **Warning**
|
||
>
|
||
> [List][list] items are also separated by whitespace, which means that function calls in list items must be enclosed by parentheses.
|
||
|
||
## Has attribute
|
||
|
||
> **Syntax**
|
||
>
|
||
> *attrset* `?` *attrpath*
|
||
|
||
Test whether [attribute set] *attrset* contains the attribute denoted by *attrpath*.
|
||
The result is a [Boolean] value.
|
||
|
||
See also: [`builtins.hasAttr`](@docroot@/language/builtins.md#builtins-hasAttr)
|
||
|
||
[Boolean]: ./types.md#type-bool
|
||
|
||
[Has attribute]: #has-attribute
|
||
|
||
After evaluating *attrset* and *attrpath*, the computational complexity is O(log(*n*)) for *n* attributes in the *attrset*
|
||
|
||
## Arithmetic
|
||
|
||
Numbers will retain their type unless mixed with other numeric types:
|
||
Pure integer operations will always return integers, whereas any operation involving at least one floating point number returns a floating point number.
|
||
|
||
Evaluation of the following numeric operations throws an evaluation error:
|
||
- Division by zero
|
||
- Integer overflow, that is, any operation yielding a result outside of the representable range of [Nix language integers](./syntax.md#number-literal)
|
||
|
||
See also [Comparison] and [Equality].
|
||
|
||
The `+` operator is overloaded to also work on strings and paths.
|
||
|
||
[arithmetic]: #arithmetic
|
||
|
||
## String concatenation
|
||
|
||
> **Syntax**
|
||
>
|
||
> *string* `+` *string*
|
||
|
||
Concatenate two [strings][string] and merge their string contexts.
|
||
|
||
[String concatenation]: #string-concatenation
|
||
|
||
## Path concatenation
|
||
|
||
> **Syntax**
|
||
>
|
||
> *path* `+` *path*
|
||
|
||
Concatenate two [paths][path].
|
||
The result is a path.
|
||
|
||
[Path concatenation]: #path-concatenation
|
||
|
||
## Path and string concatenation
|
||
|
||
> **Syntax**
|
||
>
|
||
> *path* + *string*
|
||
|
||
Concatenate *[path]* with *[string]*.
|
||
The result is a path.
|
||
|
||
> **Note**
|
||
>
|
||
> The string must not have a string context that refers to a [store path].
|
||
|
||
[Path and string concatenation]: #path-and-string-concatenation
|
||
|
||
## String and path concatenation
|
||
|
||
> **Syntax**
|
||
>
|
||
> *string* + *path*
|
||
|
||
Concatenate *[string]* with *[path]*.
|
||
The result is a string.
|
||
|
||
> **Important**
|
||
>
|
||
> The file or directory at *path* must exist and is copied to the [store].
|
||
> The path appears in the result as the corresponding [store path].
|
||
|
||
[store path]: @docroot@/store/store-path.md
|
||
[store]: @docroot@/glossary.md#gloss-store
|
||
|
||
[String and path concatenation]: #string-and-path-concatenation
|
||
|
||
## Update
|
||
|
||
> **Syntax**
|
||
>
|
||
> *attrset1* // *attrset2*
|
||
|
||
Update [attribute set] *attrset1* with names and values from *attrset2*.
|
||
|
||
The returned attribute set will have all of the attributes in *attrset1* and *attrset2*.
|
||
If an attribute name is present in both, the attribute value from the latter is taken.
|
||
|
||
[Update]: #update
|
||
|
||
## Comparison
|
||
|
||
Comparison is
|
||
|
||
- [arithmetic] for [numbers][number]
|
||
- lexicographic for [strings][string] and [paths][path]
|
||
- item-wise lexicographic for [lists][list]:
|
||
elements at the same index in both lists are compared according to their type and skipped if they are equal.
|
||
|
||
All comparison operators are implemented in terms of `<`, and the following equivalencies hold:
|
||
|
||
| comparison | implementation |
|
||
|--------------|-----------------------|
|
||
| *a* `<=` *b* | `! (` *b* `<` *a* `)` |
|
||
| *a* `>` *b* | *b* `<` *a* |
|
||
| *a* `>=` *b* | `! (` *a* `<` *b* `)` |
|
||
|
||
[Comparison]: #comparison
|
||
|
||
## Equality
|
||
|
||
- [Attribute sets][attribute set] and [lists][list] are compared recursively, and therefore are fully evaluated.
|
||
- Comparison of [functions][function] always returns `false`.
|
||
- Numbers are type-compatible, see [arithmetic] operators.
|
||
- Floating point numbers only differ up to a limited precision.
|
||
|
||
[function]: ./syntax.md#functions
|
||
|
||
[Equality]: #equality
|
||
|
||
## Logical implication
|
||
|
||
Equivalent to `!`*b1* `||` *b2*.
|
||
|
||
[Logical implication]: #logical-implication
|
||
|
||
## Pipe operators
|
||
|
||
- *a* `|>` *b* is equivalent to *b* *a*
|
||
- *a* `<|` *b* is equivalent to *a* *b*
|
||
|
||
> **Example**
|
||
>
|
||
> ```
|
||
> nix-repl> 1 |> builtins.add 2 |> builtins.mul 3
|
||
> 9
|
||
>
|
||
> nix-repl> builtins.add 1 <| builtins.mul 2 <| 3
|
||
> 7
|
||
> ```
|
||
|
||
> **Warning**
|
||
>
|
||
> This syntax is part of an
|
||
> [experimental feature](@docroot@/development/experimental-features.md)
|
||
> and may change in future releases.
|
||
>
|
||
> To use this syntax, make sure the
|
||
> [`pipe-operators` experimental feature](@docroot@/development/experimental-features.md#xp-feature-pipe-operators)
|
||
> is enabled.
|
||
> For example, include the following in [`nix.conf`](@docroot@/command-ref/conf-file.md):
|
||
>
|
||
> ```
|
||
> extra-experimental-features = pipe-operators
|
||
> ```
|
||
|
||
[Pipe operator]: #pipe-operators
|
||
[builtins]: ./builtins.md
|
||
[Function application]: #function-application
|