forked from lix-project/lix
reword descriptions of operators
add notes on semantics where appropriate
This commit is contained in:
Valentin Gagarin
parent
e07448ba6b
commit
63b640e0c2
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@ -1,36 +1,36 @@
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# Operators
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## Select
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## Attribute selection
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> *e* `.` *attrpath* \[ `or` *def* \]
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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 doesn’t exist, return *def* if provided, otherwise abort evaluation.
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Select the attribute denoted by attribute path *attrpath* from attribute set *e*.
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An attribute path is a dot-separated list of attribute names.
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If the attribute doesn’t exist, return *def* if provided, otherwise abort evaluation.
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Associativity: none
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Precedence: 1
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## Application
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## Function application
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> *e1* *e2*
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> *f* *e*
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Call function *e1* with argument *e2*.
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Call function *f* with argument *e*.
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Associativity: left
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Precedence: 2
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## Arithmetic Negation
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## Arithmetic negation
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> `-` *e*
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Arithmetic negation.
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Associativity: none
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Precedence: 3
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## Has Attribute
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## Has attribute
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> *e* `?` *attrpath*
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@ -40,11 +40,11 @@ Associativity: none
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Precedence: 4
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## List Concatenation
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## List concatenation
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> *e1* `++` *e2*
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List concatenation.
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Concatenate lists *e1* and *e2*.
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Associativity: right
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@ -54,7 +54,7 @@ Precedence: 5
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> *e1* `*` *e2*,
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Arithmetic multiplication.
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Multiply numbers *e1* and *e2*.
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Associativity: left
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@ -64,7 +64,7 @@ Precedence: 6
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> *e1* `/` *e2*
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Arithmetic division.
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Divide numbers *e1* and *e2*.
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Associativity: left
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@ -74,7 +74,7 @@ Precedence: 6
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> *e1* `+` *e2*
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Arithmetic addition.
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Add numbers *e1* and *e2*.
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Associativity: left
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@ -84,77 +84,90 @@ Precedence: 7
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> *e1* `-` *e2*
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Arithmetic subtraction.
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Subtract numbers *e2* from *e1*.
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Associativity: left
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Precedence: 7
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## String Concatenation
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## String concatenation
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> *string1* `+` *string2*
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String concatenation.
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Concatenate *string1* and *string1* and merge their string contexts.
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Associativity: left
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Precedence: 7
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## Not
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## Logical negation (`NOT`)
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> `!` *e*
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Boolean negation.
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Negate the Boolean value *e*.
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Associativity: none
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Precedence: 8
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## Update
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## Merge attribute sets
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> *e1* `//` *e2*
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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).
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Return a set consisting of all the attributes in *e1* and *e2*.
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If an attribute name is present in both, the attribute value from the former is taken.
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Associativity: right
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Precedence: 9
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## Less Than
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## Less than
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> *e1* `<` *e2*,
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Arithmetic/lexicographic comparison.
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- Arithmetic comparison for numbers
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- Lexicographic comparison for strings and paths
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- Lexicographic comparison for lists:
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Elements at the same index in both lists are compared according to their type and skipped if they are equal.
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Associativity: none
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Precedence: 10
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## Less Than or Equal To
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## Less than or equal to
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> *e1* `<=` *e2*
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Arithmetic/lexicographic comparison.
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- Arithmetic comparison for numbers
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- Lexicographic comparison for strings and paths
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- Lexicographic comparison for lists:
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Elements at the same index in both lists are compared according to their type and skipped if they are equal.
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Associativity: none
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Precedence: 10
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## Greater Than
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## Greater than
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> *e1* `>` *e2*
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Arithmetic/lexicographic comparison.
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- Arithmetic comparison for numbers
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- Lexicographic comparison for strings and paths
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- Lexicographic comparison for lists:
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Elements at the same index in both lists are compared according to their type and skipped if they are equal.
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Associativity: none
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Precedence: 10
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## Greater Than or Equal To
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## Greater than or equal to
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> *e1* `>=` *e2*
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Arithmetic/lexicographic comparison.
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- Arithmetic comparison for numbers
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- Lexicographic comparison for strings and paths
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- Lexicographic comparison for lists:
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Elements at the same index in both lists are compared according to their type and skipped if they are equal.
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Associativity: none
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@ -164,7 +177,12 @@ Precedence: 10
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> *e1* `==` *e2*
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Equality.
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Check *e1* and *e2* for equality.
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- Attribute sets and lists are compared recursively, and therefore are fully evaluated.
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- Comparison of functions always returns `false`.
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- Integers are coerced to floating point numbers if compared to floating point numbers.
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- Floating point numbers only differ up to a limited precision.
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Associativity: none
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@ -174,39 +192,40 @@ Precedence: 11
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> *e1* `!=` *e2*
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Inequality.
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Equivalent to `! (`*e1* `==` *e2* `)`
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Associativity: none
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Precedence: 11
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## Logical AND
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## Logical conjunction (`AND`)
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> *e1* `&&` *e2*
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Logical AND.
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Return `true` if and only if both `e1` and `e2` evaluate to `true`, otherwise `false`.
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Associativity: left
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Precedence: 12
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## Logical OR
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## Logical disjunction (`OR`)
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> *e1* <code>||</code> *e2*
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> *e1* `||` *e2*
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Logical OR.
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Return `true` if at least `e1` or `e2` evaluate to `true`, otherwise `false`.
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Associativity: left
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Precedence: 13
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## Logical Implication
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## Logical implication
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> *e1* `->` *e2*
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Logical implication (equivalent to <code>!e1 || e2</code>).
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Return `false` if *e1* evaluates to `true` and *e2* evaluates to `false`, otherwise `true`.
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Equivalent to `!`*e1* `||` *e2*.
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Associativity: none
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Precedence: 14
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@ -89,6 +89,8 @@
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return integers, whereas any operation involving at least one
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floating point number will have a floating point number as a result.
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Floating point numbers only differ up to a limited precision.
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- <a id="type-path" href="#type-path">Path</a>
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*Paths*, e.g., `/bin/sh` or `./builder.sh`. A path must contain at
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