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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: about 2 months ago
JSON representation
Implements a simple floating point arithmetic expression evaluator in Go (golang).
- Host: GitHub
- URL: https://github.com/soniah/evaler
- Owner: soniah
- License: bsd-3-clause
- Created: 2012-09-04T23:37:58.000Z (over 12 years ago)
- Default Branch: master
- Last Pushed: 2018-07-27T12:02:52.000Z (over 6 years ago)
- Last Synced: 2024-07-31T20:52:49.135Z (4 months ago)
- Topics: go, golang
- Language: Go
- Homepage:
- Size: 97.7 KB
- Stars: 52
- Watchers: 4
- Forks: 17
- Open Issues: 5
-
Metadata Files:
- Readme: README.md
- License: LICENSE.txt
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README
evaler
======
[](https://travis-ci.org/soniah/evaler)
[](http://gocover.io/github.com/soniah/evaler)
[](http://godoc.org/github.com/soniah/evaler)
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