How to use tab to move in a list of fields in Red language

This is similar to my earlier question ( Using TAB to move between fields in Red language ). Since I have many fields, I want to use a list of fields. However, following code is not working:

Red []

view [
    text "Value of x:"  f1: field "" on-key [handle-key event] return
    text "Value of y:"  f2: field "" on-key [handle-key event] return
    text "Third: " f3:  field "" on-key [handle-key event] return
    text "Fourth:" f4:  field "" on-key [handle-key event] return
    text "Read Sum:"    tt: text ""  on-key [handle-key event] return
    do[
        fldlist: [f1 f2 f3 f4]
        focusnum: 1
        maxfocusnum: length? fldlist
        handle-key: function [e] [
            print rejoin ["focusnum = " focusnum]   ; OUTPUT: "focusnum = none"
            k: e/key
            if k = tab [
                either e/shift? 
                    [   focusnum: focusnum - 1
                        if focusnum < 1 [focusnum: maxfocusnum]
                        win/selected: fldlist/:focusnum]
                    [   focusnum: focusnum + 1
                        if focusnum > maxfocusnum [focusnum: 1]
                        win/selected: fldlist/:focusnum]
                        ] ] ]

    button "Calculate" [
        tt/text: to-string ((to-integer f1/text) + (to-integer f2/text))      
    ]
    button "Quit" [quit]  
    do [win: self win/selected: f1]
]

The focusnum is given out as none. Where is the problem and how can this be solved.

Solution

Two modifications make your script working

fldlist: [f1 f2 f3 f4] -> fldlist: reduce [f1 f2 f3 f4

You need the 'faces' and not the words pointing to the faces.

handle-key: function [e] [

 handle-key: func [e] [
     focusnum: index? find fldlist win/selected

function makes automatically all set-words local. Therefore the local focusnum is not initialized with a value, but the global focusnum has still the start value . Finding the focusnum dynamically should cure the 'disturbance'. Probably there are more efficent ways to do so.

And here an almost final version with proper formatting

view [
    text "Value of x:"  f1: field "" on-key [handle-key event]  on-focus [handle-focus face event] return
    text "Value of y:"  f2: field "" on-key [handle-key event] on-focus [handle-focus face event] return
    text "Third: " f3:  field "" on-key [handle-key event] on-focus [handle-focus face event] return
    text "Fourth:" f4:  field "" on-key [handle-key event] on-focus [handle-focus face event] return
    text "Read Sum:"    tt: text ""  on-key [handle-key event] return
    do[
        fldlist:  reduce [f1 f2 f3 f4]
        focusnum: 1
        maxfocusnum: length? fldlist
        handle-key: func [e] [
            print rejoin ["focusnum = " focusnum]  
            k: e/key
            if k = tab [
                either e/shift?   [   
                    focusnum: focusnum - 1
                    if focusnum < 1 [focusnum: maxfocusnum]
                    set-focus  fldlist/:focusnum
                ] [   
                    focusnum: focusnum + 1
                    if focusnum > maxfocusnum [focusnum: 1]
                    set-focus  fldlist/:focusnum
                ]
            ]
        ] 
        handle-focus: func [f e] [ probe focusnum: index? find fldlist f]
    ]
    button "Calculate" [
        tt/data:  f1/data + f2/data      
    ]
    button "Quit" [quit]  
    do [win: self win/selected: f1]
]