#!/usr/bin/perl

use Tk;
use Tk::LabEntry;
use FileHandle;
use strict;

# echo "plot sin (x)" | gnuplot -persist
my $gnuplot_path = "/usr/bin/gnuplot";

my $top = new MainWindow;

my $function = "sin(x)";

my $funcentry = $top->LabEntry
  (-label        => 'Function:',
   -textvariable => \$function,
   -labelPack    => [-side => 'left'])->pack;

my $butframe   = $top->Frame->pack(-anchor => 'w');
my $plotbutton = $butframe->Button(-text => 'Plot',
				   -command => \&plot,
				  )->pack(-side => 'left');
$butframe->Button(-text => 'Quit',
		  -command => \&quit,
		 )->pack(-side => 'left');
$top->protocol('WM_DELETE_WINDOW', \&quit);

my $gnuplot = new FileHandle("| $gnuplot_path");
$gnuplot->autoflush(1);

$top->bind("<Return>", sub { $plotbutton->invoke });

MainLoop;

sub plot {
    $gnuplot->print("plot $function\n") if $function ne '';
}

sub quit {
    $gnuplot->close;
    $top->destroy;
}