- An
expression_typeis one of the following: aVARIABLE,NEGATION,CONJUNCTION,DISJUNCTION, orIMPLICATION. - An
expression_valueis one of the following:FALSE, orTRUE. - Each
expressionhas atype. - Each
VARIABLEalso has anameand avalue. NEGATIONis a unary operator, and has a single accessible child expression.CONJUNCTION,DISJUNCTION, andIMPLICATIONare binary operators, and have dual accessible child expressions.
- An
environmentis just a linked-list containingexpressionvalues.