An example of a calculator written (probably non-idomatic) factor.

calculator.factor

! Copyright (C) 2018 Andrew Owen.
! See http://factorcode.org/license.txt for BSD license.
USING: 
    ui ui.gadgets ui.gadgets.tracks ui.gadgets.labels ui.gadgets.buttons ui.gadgets.packs ui.tools.operations 
    ui.pens.solid ui.pens.gradient
    colors colors.constants 
    accessors math.parser vocabs.loader io locals 
    models models.arrow fry
    kernel strings sequences math
;

IN: calculator

TUPLE: calculator-state
    { accum initial: "" }
    { prev initial: 0 }
    { op initial: [ drop drop ] }
;

: <calculator-state> ( -- new-calc-state ) calculator-state new ;


: calc-clear-all ( state -- )
    [ accum>> "" swap set-model ] keep
    prev>> 0 swap set-model 
;

: calc-clear ( state -- ) accum>> "" swap set-model ;

:: set-calc-op ( state quot -- ) 
    state quot >>op 
    ! Move the accum value to the prev model
    [ accum>> value>> string>number ] [ prev>> ] bi set-model
    ! Clear accum
    "" state accum>> set-model
;

:: calculate ( state -- ) 
    state [ prev>> value>> ] [ accum>> value>> string>number ] bi state op>> call( x y -- result ) 
    number>string state accum>> set-model
;

: echoed ( track char model -- track ) 
    ! Char is actually a string here.
    [let :> model :> char
        char <label>
        ! The value in the model here is a string
        [ drop model dup value>> char append swap set-model ]
        <border-button> 0.33 track-add
    ]
;


:: operators-layout-init ( state -- gadget ) 
    vertical <track>
        horizontal <track> 
                "/" <label> [ drop state [ / ] set-calc-op ] <border-button> 0.5 track-add
                "AC" <label> [ drop state calc-clear-all ] <border-button> 0.5 track-add
            0.25 track-add
        horizontal <track>
                "*" <label> [ drop state [ * ] set-calc-op ] <border-button> 0.5 track-add
                "C" <label> [ drop state calc-clear ] <border-button> 0.5 track-add
            0.25 track-add
        horizontal <track>
                "-" <label> [ drop state [ - ] set-calc-op ] <border-button> 0.5 track-add
                "" <label> 0.5 track-add
            0.25 track-add
        horizontal <track>
                "+" <label> [ drop state [ + ] set-calc-op ] <border-button> 0.25 track-add
                "=" <label> [ drop state calculate ] <border-button> 0.25 track-add
            0.25 track-add 
;

:: digits-layout-init ( calculator-state -- gadget ) 
    calculator-state accum>> :> accum

    vertical <track>
        ! TODO: Figure out the way to build the tracks here.
        horizontal <track> { "7" "8" "9" } [ accum echoed ] each 0.25 track-add
        horizontal <track> { "4" "5" "6" } [ accum echoed ] each 0.25 track-add
        horizontal <track> { "1" "2" "3" } [ accum echoed ] each 0.25 track-add
        horizontal <track> { "." "0" ""  } [ accum echoed ] each 0.25 track-add 
;

:: calculator-init ( -- gadget ) 
    <calculator-state>
        "" <model> >>accum
        0 <model> >>prev 
        :> state

    vertical <track>
        state accum>> <label-control> 0.4 track-add
        horizontal <track>
            state digits-layout-init 0.6 track-add
            state operators-layout-init 0.4 track-add
        0.6 track-add
;

: calculator-show ( -- ) calculator-init "Calculator" open-window* { 200 300 } >>dim drop ;

<PRIVATE
:: alert ( message -- ) <shelf> message <label> add-gadget message open-window ;
PRIVATE>