reword descriptions of operators

add notes on semantics where appropriate
This commit is contained in:
Valentin Gagarin 2022-12-22 22:10:11 +01:00
parent e07448ba6b
commit 63b640e0c2
2 changed files with 61 additions and 40 deletions

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@ -1,36 +1,36 @@
# Operators
## Select
## Attribute selection
> *e* `.` *attrpath* \[ `or` *def* \]
Select attribute denoted by the attribute path *attrpath* from set *e*. (An attribute path is a dot-separated list of attribute names.) If the attribute doesnt exist, return *def* if provided, otherwise abort evaluation.
Select the attribute denoted by attribute path *attrpath* from attribute set *e*.
An attribute path is a dot-separated list of attribute names.
If the attribute doesnt exist, return *def* if provided, otherwise abort evaluation.
Associativity: none
Precedence: 1
## Application
## Function application
> *e1* *e2*
> *f* *e*
Call function *e1* with argument *e2*.
Call function *f* with argument *e*.
Associativity: left
Precedence: 2
## Arithmetic Negation
## Arithmetic negation
> `-` *e*
Arithmetic negation.
Associativity: none
Precedence: 3
## Has Attribute
## Has attribute
> *e* `?` *attrpath*
@ -40,11 +40,11 @@ Associativity: none
Precedence: 4
## List Concatenation
## List concatenation
> *e1* `++` *e2*
List concatenation.
Concatenate lists *e1* and *e2*.
Associativity: right
@ -54,7 +54,7 @@ Precedence: 5
> *e1* `*` *e2*,
Arithmetic multiplication.
Multiply numbers *e1* and *e2*.
Associativity: left
@ -64,7 +64,7 @@ Precedence: 6
> *e1* `/` *e2*
Arithmetic division.
Divide numbers *e1* and *e2*.
Associativity: left
@ -74,7 +74,7 @@ Precedence: 6
> *e1* `+` *e2*
Arithmetic addition.
Add numbers *e1* and *e2*.
Associativity: left
@ -84,77 +84,90 @@ Precedence: 7
> *e1* `-` *e2*
Arithmetic subtraction.
Subtract numbers *e2* from *e1*.
Associativity: left
Precedence: 7
## String Concatenation
## String concatenation
> *string1* `+` *string2*
String concatenation.
Concatenate *string1* and *string1* and merge their string contexts.
Associativity: left
Precedence: 7
## Not
## Logical negation (`NOT`)
> `!` *e*
Boolean negation.
Negate the Boolean value *e*.
Associativity: none
Precedence: 8
## Update
## Merge attribute sets
> *e1* `//` *e2*
Return a set consisting of the attributes in *e1* and *e2* (with the latter taking precedence over the former in case of equally named attributes).
Return a set consisting of all the attributes in *e1* and *e2*.
If an attribute name is present in both, the attribute value from the former is taken.
Associativity: right
Precedence: 9
## Less Than
## Less than
> *e1* `<` *e2*,
Arithmetic/lexicographic comparison.
- Arithmetic comparison for numbers
- Lexicographic comparison for strings and paths
- Lexicographic comparison for lists:
Elements at the same index in both lists are compared according to their type and skipped if they are equal.
Associativity: none
Precedence: 10
## Less Than or Equal To
## Less than or equal to
> *e1* `<=` *e2*
Arithmetic/lexicographic comparison.
- Arithmetic comparison for numbers
- Lexicographic comparison for strings and paths
- Lexicographic comparison for lists:
Elements at the same index in both lists are compared according to their type and skipped if they are equal.
Associativity: none
Precedence: 10
## Greater Than
## Greater than
> *e1* `>` *e2*
Arithmetic/lexicographic comparison.
- Arithmetic comparison for numbers
- Lexicographic comparison for strings and paths
- Lexicographic comparison for lists:
Elements at the same index in both lists are compared according to their type and skipped if they are equal.
Associativity: none
Precedence: 10
## Greater Than or Equal To
## Greater than or equal to
> *e1* `>=` *e2*
Arithmetic/lexicographic comparison.
- Arithmetic comparison for numbers
- Lexicographic comparison for strings and paths
- Lexicographic comparison for lists:
Elements at the same index in both lists are compared according to their type and skipped if they are equal.
Associativity: none
@ -164,7 +177,12 @@ Precedence: 10
> *e1* `==` *e2*
Equality.
Check *e1* and *e2* for equality.
- Attribute sets and lists are compared recursively, and therefore are fully evaluated.
- Comparison of functions always returns `false`.
- Integers are coerced to floating point numbers if compared to floating point numbers.
- Floating point numbers only differ up to a limited precision.
Associativity: none
@ -174,39 +192,40 @@ Precedence: 11
> *e1* `!=` *e2*
Inequality.
Equivalent to `! (`*e1* `==` *e2* `)`
Associativity: none
Precedence: 11
## Logical AND
## Logical conjunction (`AND`)
> *e1* `&&` *e2*
Logical AND.
Return `true` if and only if both `e1` and `e2` evaluate to `true`, otherwise `false`.
Associativity: left
Precedence: 12
## Logical OR
## Logical disjunction (`OR`)
> *e1* <code>&#124;&#124;</code> *e2*
> *e1* `||` *e2*
Logical OR.
Return `true` if at least `e1` or `e2` evaluate to `true`, otherwise `false`.
Associativity: left
Precedence: 13
## Logical Implication
## Logical implication
> *e1* `->` *e2*
> *e1* `->` *e2*
Logical implication (equivalent to <code>!e1 &#124;&#124; e2</code>).
Return `false` if *e1* evaluates to `true` and *e2* evaluates to `false`, otherwise `true`.
Equivalent to `!`*e1* `||` *e2*.
Associativity: none
Precedence: 14

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@ -89,6 +89,8 @@
return integers, whereas any operation involving at least one
floating point number will have a floating point number as a result.
Floating point numbers only differ up to a limited precision.
- <a id="type-path" href="#type-path">Path</a>
*Paths*, e.g., `/bin/sh` or `./builder.sh`. A path must contain at