Package evaler implements a simple floating point arithmetic expression evaluator.
Evaler uses Dijkstra's Shunting Yard algorithm to convert an
infix expression to postfix/RPN format, then evaluates
the RPN expression. The implementation is adapted from a Java implementation. The results
are returned as a *big.Rat.
result, err := evaler.Eval("1+2")The operators supported are:
+ - * / ^ ** () < > <= >= == !=
(^ and ** are both exponent operators)
Logical operators like < (less than) or > (greater than) get lowest precedence,
all other precedence is as expected -
BODMAS.
Logical tests like < 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.
See evaler_test.go for more examples of using operators.
The trigonometric operators supported are:
sin, cos, tan, ln, arcsin, arccos, arctan
For example:
cos(1)
sin(2-1)
sin(1)+2**2
See evaler_test.go for more examples of using trigonometric operators.
EvalWithVariables() allows variables to be passed into expressions,
for example evaluate "x + 1", where x=5.
See evaler_test.go for more examples of using variables.
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.
- floating point numbers missing leading digits (like
".5 * 2") are failing - PR's welcome
http://godoc.org/github.com/soniah/evaler
There are also a number of utility functions e.g. BigratToFloat(),
BigratToInt() that may be useful when working with evaler.
Contributions are welcome.
If you've never contributed to a Go project before here is an example workflow.
- fork this repo on the GitHub webpage
go get github.com/soniah/evalercd $GOPATH/src/github.com/soniah/evalergit remote rename origin upstreamgit remote add origin git@github.com:<your-github-username>/evaler.gitgit checkout -b developmentgit push -u origin development(setup where you push to, check it works)
Sonia Hamilton sonia@snowfrog.net
Dem Waffles dem-waffles@server.fake - trigonometric operators
Modified BSD License (BSD-3)