LablTk: basics

Create a window First of all, you have to start an application by creating the root window, to which every widget in your application will be attached: let top = openTk ()

Create a button in a window Button b must be placed somewhere inside its parent window top; we can use pack to do so: pack [b]

Note how we attach an action to clicking the button through the command argument. Here this action will cause exiting the application.

Bind actions to key strokes
When a key is pressed, it is echoed to the standard output, together with the code of the character.
Now here is the way to bind an action to the pressing of "Control-q". The action is to exit from the application.

Create a label in a window

Create a button and a label together The widgets of the button and the label have different types, and yet must belong to the same list.

It is therefore necessary to call a coercion function to cast them into a common type:
pack [Tk.coe l; Tk.coe b]
or, since we opened module Tk at the beginning of the file:
pack [coe l; coe b]

An entry widget and an exit button You can type text into an Entry widget.

A label, an entry, and an exit button A "Textvariable" serves for communicating information as a string to and from Tk widgets: let v = Textvariable.create () ;;

This Textvariable is initialized to the empty string:
Textvariable.set v "" ;;
We specify here that Label l should display the contents of the Textvariable v:
let l = Label.create ~textvariable:v top
On the other hand, the text entered into the Entry n is bound the the same Textvariable v:
let n = Entry.create ~width:10 ~relief:`Sunken ~textvariable:v top
Thus the text you type in Entry n will appear at once in the Label l.
Note that on clicking the quit button, the text you have entered is displayed on standard output before leaving.

How to retrieve the text from an Entry widget? Nearly the same example as before, except that when you click on button b ("Echo the text"), the command that is bound to b specifies that v, i.e. the stuff to be displayed on l, is to be updated using whatever you entered into n.

After entering some text		After echoing the text

Note that we have to "coe" the different widgets in order to pack them in the window.
You retrieve the texte entered into an Entry widget with Entry.get.
Clearly what you want to do with the data which are entered in an Entry, or specified through Check or Radio buttons, is off topic in the presents notes; it is the concern of your own application. As a consequence the only use we shall make here of such data will be to print them on standard output.

On my Mac (Tiger), I observed that Entry.get returns a string coded in UTF-8.
If you are sure that your text contains only latin1 characters, you can use the following recept to convert to a new chain in ISO-8859-1:

• Examine each byte of the given string in turn.
• Take the int_of_char of the byte; if it is less than 195 (i.e. binary 11000011), this is a plain ascii character, so emit this byte as is into the transformed chain.
• Otherwise it announces the beginning of an utf-8 char. Therefore take the int_of_char of the next byte, add 64, and emit the char_of_int of the result into the new chain.
• Of course this is bound to fail if your text contains other characters than latin1 (we encounter a byte with code strictly greater than 195).
• Here is a piece of code to do the job.

How to retrieve the state of a check button?

State of a check button

How to retrieve the state of a radio button?

State of a radio button

After making a choice: