Take calculation formulas as string and return the result. The token supported at the moment are : - literal numbers, such as “3” or “1.618” or “98765.4321” - constants, such as PI (3.14159) and the natural logarithmic base E (2.71828) - operations: addition “+”, subtraction “-“, multiplication “*”, division “/”, exponentiation “^” - basic trigonometry functions: sine, cosine and tangent - left and ri