https://github.com/soniah/evaler
Package evaler implements a simple floating point arithmetic expression evaluator.
Evaler uses Dijkstra's Shunting Yard algorithm [1] to convert an infix
expression to postfix/RPN format [2], then evaluates the RPN expression. The
implementation is adapted from a Java implementation at [3]. The results are
returned as a math/big *big.Rat.
This is release 2.0. The previous version that returned results as float64 is in the branch float64.
result, err := evaler.Eval("1+2")
The operators supported are:
+ - * / ** () < >
< (less than) and > (greater than) will get lowest precedence, all other precedence is as expected (BODMAS [4]).
< and > tests will evaluate to 0.0 for false and 1.0 for true, allowing expressions like:
3 * (1 < 2) # returns 3.0
3 * (1 > 2) # returns 0.0
Minus implements both binary and unary operations (thanks @hiroxy).
The math/big library doesn't have an exponent function (**), and implenting one for big.Rat numbers is non-trivial. As a work around, arguments are converted to float64's, the calculation is done using the math.Pow() function, the result is converted to a big.Rat and placed back on the stack.
http://godoc.org/github.com/soniah/evaler
There are also a number of utility functions (eg BigratToFloat(), BigratToInt()) that may be useful when working with evaler.
Sonia Hamilton
Modified BSD License (BSD-3)
[1] http://en.wikipedia.org/wiki/Shunting-yard_algorithm
[2] http://en.wikipedia.org/wiki/Reverse_Polish_notation