Operator Priority
Operator symbols
Reserved operators and keywords
Priority and associativity


This article discusses operator priority and associativity in Ela.

Operator symbols

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.

Reserved operators and keywords

The following operators and keywords are reserved and cannot be used for custom operators:
& Lazy sections if Conditional operator opentype Type declaration
-> Lambda operator then Conditional operator class Class declaration
| Guard else Conditional operator open Module import
@ 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

Priority and associativity

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