Users can define custom fixity for names/symbols. The scope of fixity definition is within the same file.
The keywords are infix, infixl, infixr, prefix, postfix and nonfix.
extern fun add (int, int): int
symintr ~>
symintr >>
infix ~> (* make ~> infix, non-assoc *)
infixl ~> add (* make ~> and `add` infix, left-assoc *)
infixl (+) ~> >> (* make ~> and >> infix, left-assoc,
having the same precedence as (+)
note that this name/symbol as to be in
parenthesis in order to be parsed as a
precedence definition *)
infixr 50 ~> >> (* make ~> and >> infix, right-assoc,
having precedence 50. *)
postfix (= + 1) ^ (* make ^ postfix, having the same
precedence as (=) plus 1.
note that the `+` need to be separated
from `=`, or it will be parsed as part
of the symbol *)
nonfix add (* make `add` nonfix, which means it can only
be used as functions from this point on. *)
Roughly speaking the syntax is as follows. (In a BNF-like syntax)
keyword ::= "infix" | "infixl" | "infixr" | "postfix" | "prefix"
opr ::= symbol | name
precedence ::= number | "(" opr (("+"|"-") number)? ")"
fixity ::= keyword precedence? opr+ | "nonfix" opr+
In addition, users can change fixity temporarily using the following syntax.
- change a name to infix, non-assoc:
name(a,b) => a \name b - change a symbol to prefix:
a + b => op+ (a, b)