REPL example app with print statement logs

logs.go

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"log"
	"os"
	"time"
)

func main() {
	log.Printf("Started the program")
	br := bufio.NewReader(os.Stdin)

	count := 1
	for {
		log.Printf("Starting entry %d", count)
		count++
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Printf("%s: A fatal error occured.", time.Now())
			log.Printf("%s", err)
		}
	}
}

func readEvaluateProcess(br *bufio.Reader) error {
	t1 := time.Now()
	fmt.Printf("> ")

	line, err := readLine(br)
	if err != nil {
		log.Printf("%s: The following error occured: %s", time.Now(), err)
		return err
	}

	out, err := processLine(line)
	if err != nil {
		log.Printf("%s: The following error occured: %s", time.Now(), err)
		return err
	}
	fmt.Printf("< %s\n\n", out)

	t2 := time.Now()
	duration := int64(t2.Sub(t1) / time.Millisecond)

	log.Printf("%s: duration in milliseconds: %d", time.Now(), duration)
	return nil
}

func readLine(br *bufio.Reader) ([]byte, error) {
	line, _, err := br.ReadLine()
	log.Printf("%s: Read line. Text entered: %s", time.Now(), line)
	if err != nil {
		log.Printf("%s: The following error occured in readLine: %s", time.Now(), line)
		return nil, err
	}

	return line, nil
}

func processLine(in []byte) (out []byte, err error) {
	output := bytes.ToUpper(in)
	log.Printf("%s: Process line. Text output: %s", time.Now(), output)
	return output, nil
}