Haskell Language Fixity declarations Binding precedence
Example
The number that follows the associativity information describes in what order the operators are applied. It must always be between 0 and 9 inclusive. This is commonly referred to as how tightly the operator binds. For example, consider the following fixity declarations (in base)
infixl 6 +
infixl 7 *
Since * has a higher binding precedence than + we read 1 * 2 + 3 as
(1 * 2) + 3
In short, the higher the number, the closer the operator will "pull" the parens on either side of it.
Remarks
-
Function application always binds higher than operators, so
f x `op` g ymust be interpreted as(f x)op(g y)no matter what the operator`op`and its fixity declaration are. -
If the binding precedence is omitted in a fixity declaration (for example we have
infixl *!?) the default is9.
