#lang scribble/manual

@title{big_bang}

Here is an example of a well-formed @tt{big_bang} clause.

@verbatim|{
big_bang(init = 2, to_draw = draw_function)
}|

Semantically, it is identical to the HtDP big-bang. Clause names
which formerly contained hyphens have been replaced with names
containing underscores (e.g. @tt{to-draw} become @tt{to_draw}).
New clauses have been added whenever an HtDP clause accepts
multiple expressions. For example, the HtDP @tt{big-bang}'s
@tt{to-draw} clause could take one expression (@tt{draw-expr}),
or three expressions (@tt{draw-expr, width-expr, height-expr}).
To enable this in Pyret, the @tt{to_draw} clause recognizes
two @emph{dependent} clauses, @tt{draw_width}, and @tt{draw_height}.
Thus, the equivalent of

@verbatim|{
(big-bang 2
          (to-draw draw_expr width_expr height_expr))
}|

is

@verbatim|{
big_bang(init = 2, to_draw = draw_expr, draw_width = width_expr, \
         draw_height = height_expr)
}|

Here is a list of the new clause names.

@verbatim|{
on_tick
tick_rate (dependent on `on_tick`)
tick_limit (dependent on `on_tick`)
on_key
on_pad
on_release
on_mouse
to_draw
draw_width (dependent on `to_draw`)
draw_height (dependent on `to_draw`)
stop_when
last_scene (dependent on `stop_when`)
check_with
on_receive
}|