Prednote.Expressions.RPN

Postfix, or RPN, expression parsing.

This module parses RPN expressions where the operands are predicates and the operators are one of and, or, or not, where and and or are binary and not is unary.

Documentation

data RPNToken a

Constructors

TokOperand (Pred a)

TokOperator Operator

Instances

Contravariant RPNToken

data Operator

Constructors

OpAnd

OpOr

OpNot

Instances

Show Operator

pushOperand :: Pred a -> [Pred a] -> [Pred a]

pushOperator :: Operator -> [Pred a] -> Either Text [Pred a]

pushToken :: [Pred a] -> RPNToken a -> Either Text [Pred a]

parseRPN :: Foldable f => f (RPNToken a) -> Either Text (Pred a)

Parses an RPN expression and returns the resulting Predbox. Fails if there are no operands left on the stack or if there are multiple operands left on the stack; the stack must contain exactly one operand in order to succeed.