main.go


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package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	var err error
	f := os.Stdin
	if len(os.Args) > 1 {
		f, err = os.Open(os.Args[1])
		if err != nil {
			panic(err)
		}
		defer f.Close()
	}
	sc := bufio.NewScanner(f)
	for sc.Scan() {
		s := sc.Bytes()
		expr, err := Parse(s)
		if err != nil {
			fmt.Fprintln(os.Stderr, "Parse:", err)
			continue
		}
		n := expr.Eval()
		fmt.Println(n.String())
	}
}