Version: 5.0
FrTime: A Language for Reactive Programs
The frtime language supports declarative construction of reactive systems in a syntax very similar to that of Racket. To interact with FrTime, select FrTime from the Choose Language menu. You can also make FrTime the language for a module:
| (module <module-name> frtime |
| <module-body>) |
| #lang frtime |
1 Primitives
stands for an undefined value.
| (undefined? val) → boolean? |
| val : any/c |
returns #t iff
val is a behavior (a time-varying value whose current value can be
projected at any time).
returns #t iff
val is an event (a time-varying stream of values that can occur
at arbitrary times).
is an event that never occurs.
2 Defining Custom Input Signals
returns a
signal whose values initially track that of init-expr, but
that may be rewired to a different signal by set-cell!.
| (event-receiver) → event? |
returns an event stream that can be
triggered imperatively by send-event.
| (send-event rcvr val) → void? |
| rcvr : event? |
| val : any/c |
3 Signal-Processing Procedures
projects the current value of
a behavior or constant.
delays val by duration milliseconds.
computes
a numeric approximation of the integral of val with respect
to time (measured in milliseconds).
| (derivative val) → behavior? |
| val : behavior? |
computes a numeric
approximation of the derivative of val with respect to time.
| |||
|
returns an event stream that fires whenever ev fires, whose
values are transformed by application of proc.
| |||
|
returns an event stream that passes through only the values from
ev for which pred returns #t.
merges all of the input
event sources into a single event source.
returns an event source that
carries only the first occurrence of ev. (The rest are
filtered out.)
returns an event source
that occurs each time the argument behavior changes. The value of the
occurrence is the behavior’s new value.
constructs a behavior that starts out as init and then
takes on the last value produced by ev
returns a behavior that starts as init. Each time
ev yields a (potentially time-varying) value, the behavior
switches to that value.
constructs an event source
by accumulating changes (carried by the given event source) over an
initial value.
combines functionality
from accum-e and hold to construct a behavior.
(accum-b ev init) is equivalent to (hold init (accum-e ev init)).
is similar to accum-e, except the transformer
function is fixed and is applied to the event occurrence and the
current accumulator (in that order).
returns an event stream that
carries an occurrence each time val changes from #f to
anything else.
provides a mechanism for applying ordinary Scheme primitives to
behaviors. If any of the vals are behaviors, returns a
behavior whose current value is always equal to (proc (value-now arg) ...). In FrTime, many Racket primitives are
implicitly lifted.
The following forms allow importation of lifted procedures that aren’t included in the basic FrTime language.
| (require (lifted module-spec proc-name ...) ...) |
| (require (lifted:nonstrict module-spec proc-name ...) ...) |
4 Fred: Functional Reactive Wrapper around GRacket
| (require frtime/gui/fred) |
| ft-frame% : class? | ||
superclass: frame% | ||
|
(new ft-frame% [label label] [ [parent parent] [width width] [height height] [x x] [y y] [style style] [enabled enabled] [border border] [spacing spacing] [alignment alignment] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height] [shown shown]]) → (is-a?/c ft-frame%) label : (or/c label-string? behavior?) parent : (or/c (is-a?/c frame%) false/c) = #f width : (or/c (integer-in 0 10000) false/c) = #f height : (or/c (integer-in 0 10000) false/c) = #f x : (or/c (integer-in -10000 10000) false/c) = #f y : (or/c (integer-in -10000 10000) false/c) = #f
style :
(listof (one-of/c 'no-resize-border 'no-caption 'no-system-menu 'hide-menu-bar 'mdi-parent 'mdi-child 'toolbar-button 'float 'metal)) = null enabled : any/c = #t border : (integer-in 0 1000) = 0 spacing : (integer-in 0 1000) = 0
alignment :
(list/c (one-of/c 'left 'center 'right) (one-of/c 'top 'center 'bottom)) = '(center top) min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = #t stretchable-height : any/c = #t shown : any/c = #f The constructor arguments are as in frame%, except that shown label, enabled, stretchable-width, and stretchable-height may be time-varying.
| ft-message% : class? | ||
superclass: message% | ||
|
(new ft-message% [label label] [parent parent] [ [style style] [font font] [enabled enabled] [vert-margin vert-margin] [horiz-margin horiz-margin] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height]]) → (is-a?/c ft-message%)
label :
(or/c label-string? behavior? (is-a?/c bitmap%) (or-of/c 'app 'caution 'stop))
parent :
(or/c (is-a?/c frame%) (is-a?/c dialog%) (is-a?/c panel%) (is-a?/c pane%)) style : (listof (one-of/c 'deleted)) = null font : (is-a?/c font%) = (scheme normal-control-font) enabled : (or/c any/c behavior?) = #t vert-margin : (integer-in 0 1000) = 2 horiz-margin : (integer-in 0 1000) = 2 min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = #f stretchable-height : any/c = #f The constructor arguments are the same as in message%, except that label, enabled, stretchable-width, and stretchable-height may be time-varying.
| ft-button% : class? | ||
superclass: button% | ||
|
(new ft-button% [label label] [parent parent] [ [style style] [font font] [enabled enabled] [vert-margin vert-margin] [horiz-margin horiz-margin] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height]]) → (is-a?/c ft-button%) label : (or/c label-string? behavior (is-a?/c bitmap%))
parent :
(or/c (is-a?/c frame%) (is-a?/c dialog%) (is-a?/c panel%) (is-a?/c pane%)) style : (one-of/c 'border 'deleted) = null font : (is-a?/c font%) = (scheme normal-control-font) enabled : any/c = #t vert-margin : (integer-in 0 1000) = 2 horiz-margin : (integer-in 0 1000) = 2 min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = #f stretchable-height : any/c = #f The constructor arguments are the same as in message%, except that label, enabled, stretchable-width, and stretchable-height may be time-varying.
(send a-ft-button get-value-e) → event? returns an event stream that yields a value whenever the user clicks the button.
| ft-check-box% : class? | ||
superclass: check-box% | ||
|
(new ft-check-box% [label label] [parent parent] [ [style style] [value value] [font font] [enabled enabled] [vert-margin vert-margin] [horiz-margin horiz-margin] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height] [value-set value-set]]) → (is-a?/c ft-check-box%) label : (or/c label-string? behavior? (is-a?/c bitmap%))
parent :
(or/c (is-a?/c frame%) (is-a?/c dialog%) (is-a?/c panel%) (is-a?/c pane%)) style : (listof (one-of/c 'deleted)) = null value : any/c = #f font : (is-a?/c font%) = (scheme normal-control-font) enabled : any/c = #t vert-margin : (integer-in 0 1000) = 2 horiz-margin : (integer-in 0 1000) = 2 min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = #f stretchable-height : any/c = #f value-set : event? = never-e The constructor arguments are the same as in check-box%, except that label, enabled, stretchable-width, and stretchable-height may be time-varying. Also, any occurrence on value-set sets the check box’s state to that of the event value.
(send a-ft-check-box get-value-b) → behavior? returns a value that always reflects the current state of the check box.
| ft-slider% : class? | ||
superclass: slider% | ||
|
(new ft-slider% [label label] [min-value min-value] [max-value max-value] [parent parent] [ [init-value init-value] [style style] [font font] [enabled enabled] [vert-margin vert-margin] [horiz-margin horiz-margin] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height] [value-set value-set]]) → (is-a?/c ft-slider%) label : (or/c label-string? behavior? false/c) min-value : (integer-in -10000 10000) max-value : (integer-in -10000 10000)
parent :
(or/c (is-a?/c frame%) (is-a?/c dialog%) (is-a?/c panel%) (is-a?/c pane%)) init-value : (integer-in -10000 10000) = min-value
style :
(listof (one-of/c 'horizontal 'vertical 'plain 'vertical-label 'horizontal-label 'deleted)) = '(horizontal) font : (is-a?/c font%) = normal-control-font enabled : any/c = #t vert-margin : (integer-in 0 1000) = 2 horiz-margin : (integer-in 0 1000) = 2 min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = (memq 'horizontal style) stretchable-height : any/c = (memq 'vertical style) value-set : event? = never-e The constructor arguments are the same as in check-box%, except that label, enabled, stretchable-width, and stretchable-height may be time-varying. Also, any occurrence on value-set sets the slider’s state to that of the event value.
(send a-ft-slider get-value-b) → behavior? returns a value that always reflects the current state of the slider.
| ft-text-field% : class? | ||
superclass: text-field% | ||
|
(new ft-text-field% [label label] [parent parent] [ [init-value init-value] [style style] [font font] [enabled enabled] [vert-margin vert-margin] [horiz-margin horiz-margin] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height] [value-set value-set]]) → (is-a?/c ft-text-field%) label : (or/c label-string? false/c)
parent :
(or/c (is-a?/c frame%) (is-a?/c dialog%) (is-a?/c panel%) (is-a?/c pane%)) init-value : string? = ""
style :
(listof (one-of/c 'single 'multiple 'hscroll 'password 'vertical-label 'horizontal-label 'deleted)) = '(single) font : (is-a?/c font%) = (scheme normal-control-font) enabled : any/c = #t vert-margin : (integer-in 0 1000) = 2 horiz-margin : (integer-in 0 1000) = 2 min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = #t stretchable-height : any/c = (memq 'multiple style) value-set : event? = never-e The constructor arguments are the same as in check-box%, except that label, enabled, stretchable-width, and stretchable-height may be time-varying. Also, any occurrence on value-set sets the text field’s state to that of the event value.
(send a-ft-text-field get-value-b) → behavior? returns a value that always reflects the current state of the text field.
| ft-radio-box% : class? | ||
superclass: radio-box% | ||
|
(new ft-radio-box% [label label] [choices choices] [parent parent] [ [style style] [selection selection] [font font] [enabled enabled] [vert-margin vert-margin] [horiz-margin horiz-margin] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height] [value-set value-set]]) → (is-a?/c ft-radio-box%) label : (or/c label-string? behavior? false/c) choices : (or/c (listof label-string?) (listof (is-a?/c bitmap%)))
parent :
(or/c (is-a?/c frame%) (is-a?/c dialog%) (is-a?/c panel%) (is-a?/c pane%))
style :
(listof (one-of/c 'horizontal 'vertical 'vertical-label 'horizontal-label 'deleted)) = '(vertical) selection : exact-nonnegative-integer? = 0 font : (is-a?/c font%) = normal-control-font enabled : any/c = #t vert-margin : (integer-in 0 1000) = 2 horiz-margin : (integer-in 0 1000) = 2 min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = #f stretchable-height : any/c = #f value-set : event? = never-e The constructor arguments are the same as in check-box%, except that label, enabled, stretchable-width, and stretchable-height may be time-varying. Also, any occurrence on value-set sets the text field’s state to that of the event value.
(send a-ft-radio-box get-selection-b) → behavior? returns a value that always reflects the currently selected element in the radio box.
| ft-choice% : class? | ||
superclass: choice% | ||
|
(new ft-choice% [label label] [choices choices] [parent parent] [ [style style] [selection selection] [font font] [enabled enabled] [vert-margin vert-margin] [horiz-margin horiz-margin] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height] [value-set value-set]]) → (is-a?/c ft-choice%) label : (or/c label-string? false/c) choices : (listof label-string?)
parent :
(or/c (is-a?/c frame%) (is-a?/c dialog%) (is-a?/c panel%) (is-a?/c pane%))
style :
(listof (one-of/c 'horizontal-label 'vertical-label 'deleted)) = null selection : exact-nonnegative-integer? = 0 font : (is-a?/c font%) = (scheme normal-control-font) enabled : any/c = #t vert-margin : (integer-in 0 1000) = 2 horiz-margin : (integer-in 0 1000) = 2 min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = #f stretchable-height : any/c = #f value-set : event? = never-e The constructor arguments are the same as in check-box%, except that label, enabled, stretchable-width, and stretchable-height may be time-varying. Also, any occurrence on value-set sets the text field’s state to that of the event value.
(send a-ft-choice get-selection-b) → behavior? returns a value that always reflects the currently selected element in the choice control.
| ft-list-box% : class? | ||
superclass: list-box% | ||
|
(new ft-list-box% [label label] [choices choices] [parent parent] [ [style style] [selection selection] [font font] [label-font label-font] [enabled enabled] [vert-margin vert-margin] [horiz-margin horiz-margin] [min-width min-width] [min-height min-height] [stretchable-width stretchable-width] [stretchable-height stretchable-height] [value-set value-set]]) → (is-a?/c ft-list-box%) label : (or/c label-string? false/c) choices : (listof label-string?)
parent :
(or/c (is-a?/c frame%) (is-a?/c dialog%) (is-a?/c panel%) (is-a?/c pane%))
style :
(listof (one-of/c 'single 'multiple 'extended 'vertical-label 'horizontal-label 'deleted)) = '(single) selection : (or/c exact-nonnegative-integer? false/c) = #f font : (is-a?/c font%) = (scheme view-control-font) label-font : (is-a?/c font%) = (scheme normal-control-font) enabled : any/c = #t vert-margin : (integer-in 0 1000) = 2 horiz-margin : (integer-in 0 1000) = 2 min-width : (integer-in 0 10000) = graphical-minimum-width min-height : (integer-in 0 10000) = graphical-minimum-height stretchable-width : any/c = #t stretchable-height : any/c = #t value-set : event? = never-e The constructor arguments are the same as in check-box%, except that label, enabled, stretchable-width, and stretchable-height may be time-varying. Also, any occurrence on value-set sets the text field’s state to that of the event value.
(send a-ft-list-box get-selection-b) → behavior? returns a value that always reflects the primary selection in the list box.
(send a-ft-list-box get-selections-b) → behavior? returns a value that always reflects the current set of selected elements in the list box.
5 Graphical Demo Programs
TODO: document the animation library itself!
To run the following animation/GUI demos, simply set the language level to FrTime, open the corresponding file, and Execute. See the demo source code for more information.
orbit-mouse.ss : A collection of balls that move in circles around the mouse pointer.
piston.ss : Simulation of a piston/cylinder.
rotation.ss : Balls moving in circles.
delay-mouse.ss : A trail of balls following the mouse.
ball-on-string.ss : A ball chasing the mouse.
pong.ss : A simple pong/air-hockey game. The left paddle moves with numeric keypad; the right paddle moves with the mouse. The ’r’ key resets the score.
pizza.ss : A simple "pizza ordering" user interface based on an HtDP exercise.
calculator.ss : A simple calculator interface, also based on an HtDP exercise except that the result updates continuously as the arguments and operator change.
The next three animation examples are courtesy of Robb Cutler:
analog-clock.ss : An animated real-time clock. A slider adjusts the radius of the face. Click and drag to move the face around.
growing-points.ss : A field of points that grow as the mouse approaches.
needles.ss : A field of needles that point at the mouse.