goexp

Recursive descent expression parser in Go

Installation

go get -u github.com/svstanev/goexp

Usage

package main
import (
    "fmt"
    "math"
    "github.com/svstanev/goexp"
    "github.com/svstanev/goexp/types"
)
func main() {
    context := goexp.NewEvalContext(nil)
    context.AddName("x", types.Integer(1))
    context.AddName("y", types.Integer(3))
    context.AddName("z", types.Integer(5))
    context.AddMethod("max", func(args ...types.Integer) (interface{}, error) {
        var res int64 = math.MinInt64
        for _, value := range args {
            n := int64(value)
            if n > res {
                res = n
            }
        }
        return types.Integer(res), nil
    })
    res, err := goexp.EvalString("max(x, y, z)", context)
    if err != nil {
        panic(err)
    }
    fmt.Println(res)
}

Expression language

Syntax Grammar

expression      -> logical_or
logical_or      -> logical_and (("||") logical_and)*;
logical_and     -> logical_not (("&&") logical_not)*;
logical_not            -> "!"? equality;
equality        -> comparison (("==" | "!=") comparison)*;
comparison      -> addition (("<" | "<=" | ">" | ">=") addition)*;
addition        -> multiplication (("+" | "-") multiplication)*;
multiplication  -> negate (("*" | "/" | "%") negate)*;
power                     -> negate ("**" negate)*;
negate          -> "-"? call;
call            -> primary (("(" arguments? ")") | ("." IDENTIFIER))*;
primary         -> "false" | "true" | "nil" | IDENTIFIER | NUMBER | STRING | "(" expression ")";
arguments       -> expression ("," expression)*;

Lexical Grammar

IDENTIFIER      -> ALPHA (ALPHA | DIGIT)*;
NUMBER          -> DIGIT* ("." DIGIT*)?;
STRING          -> "'" <any char except "'">* "'"
                  | '"' <any char except '"'>* '"';
DIGIT           -> '0'...'9'
ALPHA           -> 'a'...'z'|'A'...'Z'|'_'