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Fixities

Fixities in Juvix refer to the precedence and associativity of operators. A fixity declaration is defined using the syntax keyword followed by fixity. It specifies how an operator should be parsed in relation to other operators.

Syntax of Fixity Declaration

The syntax for a fixity declaration varies based on the operator's arity, associativity, and precedence.

Arity Declaration

For an operator with no specified precedence or associativity, the arity can be declared as follows:

syntax fixity <name> := <arity>;

In this syntax,

  • <name> represents the operator name, and
  • <arity> can either be none, unary, or binary.

This declaration is equivalent to:

syntax fixity <name> := <arity> {};

Associativity Declaration

For an operator with no specified precedence, its associativity can be declared as:

syntax fixity <name> := <arity> { assoc := <associativity> };

Here, <associativity> can either be left, right, or none.

Precedence Declaration

For an operator with no specified associativity, its precedence can be declared relative to other operators.

  • If it has equal precedence to another operator:
syntax fixity <name> := <arity> { same := otherOperatorName };
  • If it has higher precedence than other operators:
syntax fixity <name> := <arity> {
    above := [otherOperatorName1;...; otherOperatorNameN] };
  • If it has lower precedence than other operators:
syntax fixity <name> := <arity> {
    below := [otherOperatorName1;...; otherOperatorNameN] };

Associativity and Precedence Declaration

For an operator with both associativity and precedence:

syntax fixity <name> := <arity> {
    assoc := <associativity>;
    above := [otherOperatorName1;...; otherOperatorNameN]
    };

Operator Alias Fixity

In Juvix, when an operator is aliased, the new alias automatically inherits the fixity of the original operator. This behavior ensures consistency and predictability when using aliases in place of their corresponding operators.

Consider a scenario where the or operator is an alias of the || operator. The or operator will inherit the fixity of the || operator by default.

syntax alias or := ||;

newor (a b c : Bool) : Bool := (a or b) or c;

However, if you want to override this behavior, you can declare the alias with none as its fixity. Make sure to import Stdlib.Data.Fixity.

import Stdlib.Data.Fixity open;

syntax operator or none;

syntax alias or := ||;

or3 (a b c : Bool) : Bool := or (or a b) c;

Examples of Fixity Declarations

Here are some examples of common fixity declarations for operators in Juvix's standard library.

syntax fixity rapp := binary {assoc := right};

syntax fixity lapp := binary {assoc := left; same := rapp};

syntax fixity seq := binary {assoc := left; above := [lapp]};

syntax fixity functor := binary {assoc := right};

syntax fixity logical := binary {assoc := right; above := [seq]};

syntax fixity comparison := binary {assoc := none; above := [logical]};

syntax fixity pair := binary {assoc := right};

syntax fixity cons := binary {assoc := right; above := [pair]};

syntax fixity step := binary {assoc := right};

syntax fixity range := binary {assoc := right; above := [step]};

syntax fixity additive := binary {
  assoc := left;
  above := [comparison; range; cons];
};

syntax fixity multiplicative := binary {assoc := left; above := [additive]};

syntax fixity composition := binary {assoc := right; above := [multiplicative]};