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Operator Priority
This article discusses operator priority and associativity in Ela.
In Ela operator identifiers can include only the following symbols: $!%&*+-.:/\<=>?@^|~. Some of the symbols are already used by
language constructs. For example, it is not possible to define an operator & as soon as the one is already used to denote lazy lists
and lazy expressions. However it is possible to define an operator &=, etc. All standard arithmetic operators such as +, -, etc.,
composition operators, application operators and so on are not syntax but functions defined in prelude and therefore can be easily redefined.
The following operators and keywords are reserved and cannot be used for custom operators:
| Keyword | Description | Keyword | Description | Keyword | Description |
|---|---|---|---|---|---|
& |
Lazy sections | if |
Conditional operator | opentype |
Type declaration |
-> |
Lambda operator | then |
Conditional operator | class |
Class declaration |
| ` | ` | Guard | else |
Conditional operator | open |
@ |
As-pattern | is |
Type check operator | import |
Module import |
= |
Binding | let |
Local bindings | try |
Exception handling |
\ |
Lambda operator | in |
Local bindings | with |
Pattern matching |
\\ |
Comprehension operator | where |
Local bindings | match |
Pattern matching |
<- |
Comprehension selector | instance |
Instance declaration | ||
.. |
Ranges | deriving |
Deriving clause | ||
. |
Member access | type |
Type declaration | ||
::: |
Context | data |
Type declaration |
In Ela operator priority and associativity is controlled by the first symbols in operator identifier. The following table lists all operator
priorities in order, starting from the loose operators. A notation {op} is used to show that any number (zero or more) of trailing operator
symbols is allowed here. For example, priroty of operators =| and =|| is the same.
| Operator Symbols | Priority | Associativity |
|---|---|---|
| | {op} | 0 | Right |
, {op} |
1 | Left |
; {op} |
1 | Left |
$ {op} |
1 | Left |
| |> {op} | 1 | Left |
| | {op} | 2 | Left |
& {op} |
3 | Left |
= {op} |
4 | Left |
< {op} |
4 | Left |
> {op} |
4 | Left |
^ {op} |
5 | Left |
@ {op} |
6 | Right |
# {op} |
6 | Right |
+ {op} |
7 | Left |
- {op} |
7 | Left |
* {op} |
8 | Left |
/ {op} |
8 | Left |
% {op} |
8 | Left |
| (infix application) | 9 | Left |
<< {op} |
10 | Right |
: {op} |
10 | Right |
>> {op} |
11 | Left |
~ {op} |
12 | Left |
! {op} |
12 | Left |
? {op} |
12 | Left |
. {op} |
12 | Left |
::: |
13 | Left |
| (application) | 13 | Left |