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https://github.com/soniah/evaler

Implements a simple floating point arithmetic expression evaluator in Go (golang).
https://github.com/soniah/evaler

go golang

Last synced: 24 days ago
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Implements a simple floating point arithmetic expression evaluator in Go (golang).

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README 

        
evaler

======



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https://github.com/soniah/evaler



Package evaler implements a simple floating point arithmetic expression evaluator.



Evaler uses Dijkstra's [Shunting Yard algorithm](http://en.wikipedia.org/wiki/Shunting-yard_algorithm) to convert an

infix expression to [postfix/RPN format](http://en.wikipedia.org/wiki/Reverse_Polish_notation), then evaluates

the RPN expression. The implementation is adapted from a [Java implementation](http://willcode4beer.com/design.jsp?set=evalInfix). The results

are returned as a `*big.Rat`.



Usage

-----



```go

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](http://www.mathsisfun.com/operation-order-bodmas.html).



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](https://github.com/soniah/evaler/fork)

1. `go get github.com/soniah/evaler`

1. `cd $GOPATH/src/github.com/soniah/evaler`

1. `git remote rename origin upstream`

1. `git remote add origin [email protected]:/evaler.git`

1. `git checkout -b development`

1. `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