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Fractional precedence, so that it's always possible to squeeze an operator precedence between two existing precedences. Ranges over [-20, 120] . A normal operator should have a precedence within [0, 100) . It might be useful to have a negative precedence if you're trying to model some already existing system, for example in Haskell ($) has precedence 0 , but clearly if b then y else f $ x should be rendered without any parens, hence the precedence of if_then_else_ is less than 0, i.e. negative.

The precedence of juxtaposition is 100 . Normally you want juxtaposition to have the highest precedence, but some languages have operators that bind tighter than juxtaposition, e.g. Haskell's postfix _{_} : f z { x = y } means f (z {x = y}) .

Associativity of an operator.

Fixity of an operator.

We allow unary operators to have associativity, because it's useful to distinguish between an expression like -(-x) (unary minus, left-associative) and ~~b (boolean NOT, right-associative).

Associativity of unary operators also matters when pretty-printing expressions like (-x) + y , which is pretty-printed as -x + y , assuming unary minus has the same fixity as + (and both the operators are left-associative). I.e. unary minus is handled just like the binary one: (0 - x) + y is pretty-printed as 0 - x + y .

Postfix operators are handled similarly. E.g. if ! is left-associative, then (x!)! is pretty-printed as x!! and if it's right-associative -- (x!)! .

The data type is parameterized, so that the user can choose precedence to be integer/fractional, bounded/unbounded, etc (we could also allows operators to be partially or totally ordered, but at the moment prec is required to implement Ord , i.e. it has to be totally ordered). By default we go with bounded fractional precedence, see the main Text.Fixity module.

FixityOver instantiated at Precedence .

Direction in which pretty-printing goes. For example in x + y x is pretty-printed to the left of + and y is pretty-printed to the right of + .

A context that an expression is being rendered in.

FixityOver instantiated at Precedence .

Enclose an a (using the provided function) if required or leave it as is. The need for enclosing is determined from an outer RenderContext and the inner fixity.

A fixity with the lowest precedence. When used as a part of an outer context, never causes addition of parens.

The fixity of juxtaposition.

The fixity of a unitary expression which is safe to render without parens in any context.

A fixity with the highest precedence. When used as a part of an outer context, always causes addition of parens.

An initial RenderContext . An expression printed in this context never gets enclosed in parens.

An initial RenderContext . An expression printed in this context always gets enclosed in parens.