Prednote.Expressions

Handles parsing of both infix and RPN Predbox expressions.

Documentation

data ExprDesc

Is this an infix or RPN expression?

Constructors

Infix

RPN

Instances

Eq ExprDesc

Show ExprDesc

type Error = Text

data Token a

A single type for both RPN tokens and infix tokens.

Instances

Contravariant Token

operand :: Pred a -> Token a

Creates Operands from Predbox.

opAnd :: Token a

The And operator

opOr :: Token a

The Or operator

opNot :: Token a

The Not operator

openParen :: Token a

Open parentheses

closeParen :: Token a

Close parentheses

parseExpression :: ExprDesc -> [Token a] -> Either Error (Pred a)

Parses expressions. Fails if the expression is nonsensical in some way (for example, unbalanced parentheses, parentheses in an RPN expression, or multiple stack values remaining.) Works by first changing infix expressions to RPN ones.