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doc/Expr.adoc: description of the selector operator; added operators to the priority table

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Celestino Amoroso 2024-05-06 04:24:17 +02:00
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@ -169,7 +169,7 @@ x = 1; y = 2*x
== Other operations == Other operations
=== [blue]`;` operator === [blue]`;` operator
The semicolon operator [blue]`;` is an infixed operator. It evaluates the left expression first and then the right expression. The latter is the final result. The semicolon operator [blue]`;` is an infixed pseudo-operator. It evaluates the left expression first and then the right expression. The latter is the final result.
IMPORTANT: Technically [blue]`;` is not treated as a real operator. It acts as a separator in lists of expressions. IMPORTANT: Technically [blue]`;` is not treated as a real operator. It acts as a separator in lists of expressions.
@ -187,7 +187,7 @@ a=1; b=2; c=3; a+b+c // returns 6
[blue]`but` is very similar to [blue]`;`. The only difference is that [blue]`;` can't be used inside parenthesis [blue]`(` and [blue]`)`. [blue]`but` is very similar to [blue]`;`. The only difference is that [blue]`;` can't be used inside parenthesis [blue]`(` and [blue]`)`.
=== Assignment operator [blue]`=` === Assignment operator [blue]`=`
The assignment operator [blue]`=` is used to define variable in the evaluation context or to change their value (see _ExprContext_). The assignment operator [blue]`=` is used to define variables in the evaluation context or to change their value (see _ExprContext_).
The value on the left side of [blue]`=` must be an identifier. The value on the right side can be any expression and it becomes the result of the assignment operation. The value on the left side of [blue]`=` must be an identifier. The value on the right side can be any expression and it becomes the result of the assignment operation.
.Example .Example
@ -202,13 +202,22 @@ The _selector operator_ is very similar to the _switch/case/default_ statement a
.Syntax .Syntax
[source,bnf] [source,bnf]
---- ----
<selector-operator> ::= <expression> "?" <selector-case> { ":" <selector-case> } ["::" <case-value>] <selector-operator> ::= <select-expression> "?" <selector-case> { ":" <selector-case> } ["::" <default-multi-expression>]
<selector-case> ::= [<list>] <case-value> <selector-case> ::= [<match-list>] <case-value>
<case-value> ::= "{" <multi-expr> "}" <match-list> ::= "["<item>{","<items>}"]"
<multi-expr> ::= <expr> {";" <expr>} <item> ::= <expression
<case-multi-expression> ::= "{" <multi-expression> "}"
<multi-expression> ::= <expression> {";" <expression>}
---- ----
.Example In other words, the selector operator evaluates the expression (`<select-expression>`) on the left-hand side of the `?` symbol; it then compares the result obtained with the values listed in the `<match-list>`'s. If the comparision find a match with a value in a match-list, the associated `<case-multi-expression>` is evaluted, and its result will be the final result of the selection operation.
The match lists are optional. In that case, the position, from left to right, of the `<selector-case>` is used as match-list. Of course, that only works if the select-expression results in an integer.
The `:` symbol (colon) is the separator of the selector-cases. Note that if the value of the select-expression does not match any match-list, an error will be issued. Therefore, it is strongly recommended to provide a default (multi-)expression introduced by the `::` symbol (double-colon). Also note that the default expression has no match-list.
.Examples
[source,go] [source,go]
---- ----
1 ? {"a"} : {"b"} // returns "b" 1 ? {"a"} : {"b"} // returns "b"
@ -224,33 +233,38 @@ The _selector operator_ is very similar to the _switch/case/default_ statement a
The table below shows all supported operators by decreasing priorities. The table below shows all supported operators by decreasing priorities.
.Operators priorities .Operators priorities
[cols="^2,^2,^2,^5,<5"] [cols="^2,^2,^2,^5,^5"]
|=== |===
| Priority | Operators | Position | Operation | Operands and results | Priority | Operators | Position | Operation | Operands and results
1+|*FACT*| [blue]`!` | _Postfix_ | _Factorial_| _integer_ "!" -> _integer_ .1+|*ITEM*| [blue]`.` | _Infix_ | _Item_| _collection_ `"."` _key_ -> _any_
1+|*SIGN*| [blue]`+`, [blue]`-` | _Prefix_ | _Change-sign_| ("+"\|"-") _number_ -> _number_ .2+|*INC*| [blue]`++` | _Postfix_ | _Post increment_| _integer-variable_ `"++"` -> _integer_
.5+|*PROD*| [blue]`*` | _Infix_ | _Product_ | _number_ "*" _number_ -> _number_ | [blue]`++` | _Postfix_ | _Next item_ | _iterator_ `"++"` -> _any_
| [blue]`*` | _Infix_ | _String-repeat_ | _string_ "*" _integer_ -> _string_ .1+|*FACT*| [blue]`!` | _Postfix_ | _Factorial_| _integer_ `"!"` -> _integer_
| [blue]`/` | _Infix_ | _Division_ | _number_ "/" _number_ -> _number_ .3+|*SIGN*| [blue]`+`, [blue]`-` | _Prefix_ | _Change-sign_| (`"+"`\|`"-"`) _number_ -> _number_
| [blue]`./` | _Infix_ | _Float-division_ | __number__ "./" _number_ -> _float_ | [blue]`#` | _Prefix_ | _Lenght-of_ | `"#"` _collection_ -> _integer_
| [blue]`%` | _Infix_ | _Integer-remainder_ | _integer_ "%" _integer_ -> _integer_ | [blue]`#` | _Prefix_ | _Size-of_ | `"#"` _iterator_ -> _integer_
.5+|*SUM*| [blue]`+` | _Infix_ | _Sum_ | _number_ "+" _number_ -> _number_ .5+|*PROD*| [blue]`*` | _Infix_ | _Product_ | _number_ `"*"` _number_ -> _number_
| [blue]`+` | _Infix_ | _String-concat_ | (_string_\|_number_) "+" (_string_\|_number_) -> _string_ | [blue]`*` | _Infix_ | _String-repeat_ | _string_ `"*"` _integer_ -> _string_
| [blue]`+` | _Infix_ | _List-join_ | _list_ "+" _list_ -> _list_ | [blue]`/` | _Infix_ | _Division_ | _number_ `"/"` _number_ -> _number_
| [blue]`-` | _Infix_ | _Subtraction_ | _number_ "-" _number_ -> _number_ | [blue]`./` | _Infix_ | _Float-division_ | __number__ `"./"` _number_ -> _float_
| [blue]`-` | _Infix_ | _List-difference_ | _list_ "-" _list_ -> _list_ | [blue]`%` | _Infix_ | _Integer-remainder_ | _integer_ `"%"` _integer_ -> _integer_
.6+|*RELATION*| [blue]`<` | _Infix_ | _less_ | _comparable_ "<" _comparable_ -> _boolean_ .5+|*SUM*| [blue]`+` | _Infix_ | _Sum_ | _number_ `"+"` _number_ -> _number_
| [blue]`\<=` | _Infix_ | _less-equal_ | _comparable_ "\<=" _comparable_ -> _boolean_ | [blue]`+` | _Infix_ | _String-concat_ | (_string_\|_number_) `"+"` (_string_\|_number_) -> _string_
| [blue]`>` | _Infix_ | _greater_ | _comparable_ ">" _comparable_ -> _boolean_ | [blue]`+` | _Infix_ | _List-join_ | _list_ `"+"` _list_ -> _list_
| [blue]`>=` | _Infix_ | _greater-equal_ | _comparable_ ">=" _comparable_ -> _boolean_ | [blue]`-` | _Infix_ | _Subtraction_ | _number_ `"-"` _number_ -> _number_
| [blue]`==` | _Infix_ | _equal_ | _comparable_ "==" _comparable_ -> _boolean_ | [blue]`-` | _Infix_ | _List-difference_ | _list_ `"-"` _list_ -> _list_
| [blue]`!=` | _Infix_ | _not-equal_ | _comparable_ "!=" _comparable_ -> _boolean_ .6+|*RELATION*| [blue]`<` | _Infix_ | _less_ | _comparable_ `"<"` _comparable_ -> _boolean_
.1+|*NOT*| [blue]`not` | _Prefix_ | _not_ | "not" _boolean_ -> _boolean_ | [blue]`\<=` | _Infix_ | _less-equal_ | _comparable_ `"\<="` _comparable_ -> _boolean_
.2+|*AND*| [blue]`and` | _Infix_ | _and_ | _boolean_ "and" _boolean_ -> _boolean_ | [blue]`>` | _Infix_ | _greater_ | _comparable_ `">"` _comparable_ -> _boolean_
| [blue]`&&` | _Infix_ | _and_ | _boolean_ "&&" _boolean_ -> _boolean_ | [blue]`>=` | _Infix_ | _greater-equal_ | _comparable_ `">="` _comparable_ -> _boolean_
.2+|*OR*| [blue]`or` | _Infix_ | _or_ | _boolean_ "or" _boolean_ -> _boolean_ | [blue]`==` | _Infix_ | _equal_ | _comparable_ `"=="` _comparable_ -> _boolean_
| [blue]`\|\|` | _Infix_ | _or_ | _boolean_ "\|\|" _boolean_ -> _boolean_ | [blue]`!=` | _Infix_ | _not-equal_ | _comparable_ `"!="` _comparable_ -> _boolean_
.1+|*NOT*| [blue]`not` | _Prefix_ | _not_ | `"not"` _boolean_ -> _boolean_
.2+|*AND*| [blue]`and` | _Infix_ | _and_ | _boolean_ `"and"` _boolean_ -> _boolean_
| [blue]`&&` | _Infix_ | _and_ | _boolean_ `"&&"` _boolean_ -> _boolean_
.2+|*OR*| [blue]`or` | _Infix_ | _or_ | _boolean_ `"or"` _boolean_ -> _boolean_
| [blue]`\|\|` | _Infix_ | _or_ | _boolean_ `"\|\|"` _boolean_ -> _boolean_
.1+|*ASSIGN*| [blue]`=` | _Infix_ | _assignment_ | _identifier_ "=" _any_ -> _any_ .1+|*ASSIGN*| [blue]`=` | _Infix_ | _assignment_ | _identifier_ "=" _any_ -> _any_
.1+|*BUT*| [blue]`but` | _Infix_ | _but_ | _any_ "but" _any_ -> _any_ .1+|*BUT*| [blue]`but` | _Infix_ | _but_ | _any_ "but" _any_ -> _any_
|=== |===