https://github.com/shadowspore/calculon
Simple math expression library
https://github.com/shadowspore/calculon
evaluation expression go
Last synced: 21 days ago
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Simple math expression library
- Host: GitHub
- URL: https://github.com/shadowspore/calculon
- Owner: shadowspore
- Created: 2020-11-02T13:59:57.000Z (over 4 years ago)
- Default Branch: master
- Last Pushed: 2021-05-13T19:30:29.000Z (about 4 years ago)
- Last Synced: 2025-04-01T01:51:09.402Z (2 months ago)
- Topics: evaluation, expression, go
- Language: Go
- Homepage:
- Size: 33.2 KB
- Stars: 6
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# calculon
Simple math expression library
## Example
```go
package main
import (
"fmt"
"github.com/xjem/calculon"
)
func main() {
expr, err := calculon.Parse("sin(Pi/x)")
if err != nil {
panic(err)
}
// MathContext have math std variables and functions
// such as sin, cos, Pi, etc
ctx := calculon.MathContext()
ctx.SetVar("x", 2) // set variable
result, err := expr.Eval(ctx)
if err != nil {
panic(err)
}
fmt.Println(result) // 1
}
```
## REPL
Interactive calculator in ```cmd/repl```
```
>> 2 * -(3 + 4)
-14
>> kek = 1337
>> kek
1337
>> f(x) = x * kek
>> f(2)
2674
>> foo(x, y) = sin(f(x))^y
>> foo(1, 2)
0.9376714427474894
>> foo(f(2), 0)
1
>> ...
```
## About implementation
### Parsing
Parser uses [recursive descent algorithm](https://en.wikipedia.org/wiki/Recursive_descent_parser).\
I didn't use shunting-yard algorithm because it uses [some hacky solutions](https://stackoverflow.com/a/17132657) to handle unary minus operator, which may conflict with user-defined variables or functions.
### Interpreter
It's a tree-walking interpreter.
Each AST node have ```Eval()``` function.
## Links
1. [Java expression evaluator](https://stackoverflow.com/a/26227947)
2. [Writing a Simple Math Expression Engine in C#](https://medium.com/@toptensoftware/writing-a-simple-math-expression-engine-in-c-d414de18d4ce)
3. [Pretty Printing AST with Minimal Parentheses](https://stackoverflow.com/questions/13708837/pretty-printing-ast-with-minimal-parentheses)
4. [Shunting-yard algorithm](https://rosettacode.org/wiki/Parsing/Shunting-yard_algorithm#Go)