úÎ×Z  Safe-InferedJThe Expr data type provides a basis for ordering mathematical operations. evaluateExpressionB evaluates a mathematical expression s using the variable map m.  stringToExprC parses an expression and returns an expression tree of type Expr. evaluate? takes a map and expression tree to produce a numerical value.       ParserFunction-0.0.6,Text.ParserCombinators.Parsec.ParserFunctionExprevaluateExpression stringToExpr buildExprexpressionTablefactor variablesnumberevaluate