demo - What can you do in 30 lines of Go? Can you create a useful, complete program that demonstrates its features?

Question

question from:https://stackoverflow.com/questions/1735073/what-can-you-do-in-30-lines-of-go-can-you-create-a-useful-complete-program-tha

Answer 1

This makes a PNG (on stdout) of a clock face showing the current time. It's barely golfed to fit thirty lines, so the code is not quite as clean as it should be.

package main
import ("image"; "image/png"; "math"; "bufio"; "os"; "time")
const clock_size = 200;
const radius = clock_size / 3;
var colour image.RGBAColor;
func circle (clock *image.RGBA) {
    for angle := float64(0); angle < 360; angle++ {
        radian_angle := math.Pi * 2 * angle / 360;
        x := radius * math.Sin (radian_angle) + clock_size/2;
        y := radius * math.Cos (radian_angle) + clock_size/2;
        clock.Set (int (x), int (y), colour);}}
func hand (clock *image.RGBA, angle float64, length float64) {
    radian_angle := math.Pi * 2 * angle;
    x_inc := math.Sin (radian_angle);
    y_inc := -math.Cos (radian_angle);
    for i := float64(0); i < length; i++ {
        x := i * x_inc + clock_size/2;
        y := i * y_inc + clock_size/2;
        clock.Set (int (x), int (y), colour);}}
func main () {
    clock := image.NewRGBA (clock_size, clock_size);
    colour.A = 255;
    circle (clock);
    time := time.LocalTime ();
    hand (clock, (float64(time.Hour) + float64(time.Minute)/60)/12, radius*0.6); // hour hand
    hand (clock, (float64(time.Minute) + float64(time.Second)/60)/60, radius*0.8); // minute hand
    out := bufio.NewWriter(os.Stdout);
    defer out.Flush();
    png.Encode(out, clock);
}

Run it like

8.out > clock.png

Notice all those float64 casts? I've NEVER seen a language as strict as Go about types.

---

This is the same code fixed with go fix (and some manual tweaking) and then automatically formatted using go fmt. Some newlines where inserted manually.

package main

import (
    "bufio"
    "image"
    "image/color"
    "image/png"
    "math"
    "os"
    "time"
)

const clock_size = 200
const radius = clock_size / 3

var colour color.RGBA

func circle(clock *image.RGBA) {
    for angle := float64(0); angle < 360; angle++ {
        radian_angle := math.Pi * 2 * angle / 360
        x := radius*math.Sin(radian_angle) + clock_size/2
        y := radius*math.Cos(radian_angle) + clock_size/2
        clock.Set(int(x), int(y), colour)
    }
}

func hand(clock *image.RGBA, angle float64, length float64) {
    radian_angle := math.Pi * 2 * angle
    x_inc := math.Sin(radian_angle)
    y_inc := -math.Cos(radian_angle)
    for i := float64(0); i < length; i++ {
        x := i*x_inc + clock_size/2
        y := i*y_inc + clock_size/2
        clock.Set(int(x), int(y), colour)
    }
}

func main() {
    clock := image.NewRGBA(image.Rect(0, 0, clock_size, clock_size))
    colour.A = 255
    circle(clock)
    time := time.Now()
    hand(clock, (float64(time.Hour())+float64(time.Minute())/60)/12, radius*0.6)   // hour hand
    hand(clock, (float64(time.Minute())+float64(time.Second())/60)/60, radius*0.8) // minute hand
    out := bufio.NewWriter(os.Stdout)
    defer out.Flush()
    png.Encode(out, clock)
}