Implements a simple floating point arithmetic expression evaluator in Go (golang).

evaler

Build Status Coverage GoDoc https://github.com/soniah/evaler

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.

Usage

result, err := evaler.Eval("1+2")

Operators

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.

Trigonometric 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.

Variables

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.

Issues

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

Documentation

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

Contributions are welcome.

If you've never contributed to a Go project before here is an example workflow.

  1. fork this repo on the GitHub webpage
  2. go get github.com/soniah/evaler
  3. cd $GOPATH/src/github.com/soniah/evaler
  4. git remote rename origin upstream
  5. git remote add origin [email protected]:<your-github-username>/evaler.git
  6. git checkout -b development
  7. git push -u origin development (setup where you push to, check it works)

Author

Sonia Hamilton [email protected]

Dem Waffles [email protected] - trigonometric operators

License

Modified BSD License (BSD-3)

Links

[1] http://en.wikipedia.org/wiki/Shunting-yard_algorithm

[2] http://en.wikipedia.org/wiki/Reverse_Polish_notation

[3] http://willcode4beer.com/design.jsp?set=evalInfix

[4] http://www.mathsisfun.com/operation-order-bodmas.html

Owner
Sonia Hamilton
Australian IT professional; ex-Google; ex gosnmp maintainer
Sonia Hamilton
https://github.com/soniah/evaler
Comments
  • Support unary minus.

    Support unary minus.

    Hi @soniah

    I've enhanced the library to support unary minus. If this enhancement has worth for the library, could you review the code and merge it into master?

  • Add support for variables

    Add support for variables

    The Eval function should also accept a hashmap of string -> float64 for passing variables and their values in. This should use a symboltable under the covers.

    I will likely work on this feature.

  • fails w/o initial zeros

    fails w/o initial zeros

    .5 * 2 comes out as 10 fix is var fp_rx = regexp.MustCompile(([0-9]*\.?[0-9]+))
    I believe. (and add a test like): {".5 * 2", big.NewRat(1, 1), true}, // no leading zero

    tried to submit, but I clearly dont know how to use github yet...so submitting as issue. -s

  • Expression fails with wrong result

    Expression fails with wrong result

    This test case leads to a wrong result:

    {"2*6**3+4**6", big.NewRat(4528, 1), true},

    got 8624/1 expected 4528/1.

    https://www.google.com/search?q=2*6^3%2B4^6

    I think it's a problem in convert2postfix.

  • allow variable names to contain numbers

    allow variable names to contain numbers

    Unfortunately it gives an error if I try to pass a variable name which has a number in it; For example, a map with {"catX":"33"} evaluates fine; but if I pass: {"cat1":"33"} it says that there is no such variable "cat", ignoring the number in the name

    if there is no way to solve this, maybe indicate that in the "readme" file

  • pass two or more variables to expression,it doesn't work

    pass two or more variables to expression,it doesn't work

    for k := range symbolTable { s += k } symbols_rx = regexp.MustCompile(fmt.Sprintf("(%s)", s)) func Tokenis (expr string) []string { if symbols_rx != nil { spaced = symbols_rx.ReplaceAllString(spaced, " ${1} ")//it doesn't work } }

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