This section describes the GUI tools that Redex provides for
exploring reduction sequences.
This function opens a new window and inserts each expression
, then expr
is treated as a single
expression). Then, it reduces the terms until at least
(see below) different terms are
found, or no more reductions can occur. It inserts each new
term into the gui. Clicking the reduce
more terms are found.
The pred function indicates if a term has a particular
property. If it returns #f, the term is displayed with a
pink background. If it returns a string or a color% object,
the term is displayed with a background of that color (using
the-color-database to map the string to a color). If it
returns any other value, the term is displayed normally. If
the pred function accepts two arguments, a term-node
corresponding to the term is passed to the predicate. This
lets the predicate function explore the (names of the)
reductions that led to this term, using term-node-children,
term-node-parents, and term-node-labels.
The pred function may be called more than once per node. In
particular, it is called each time an edge is added to a
node. The latest value returned determines the color.
The pp function is used to specially print expressions. It
must either accept one or four arguments. If it accepts one
argument, it will be passed each term and is expected to
return a string to display the term.
If the pp function takes four arguments, it should render
its first argument into the port (its second argument) with
width at most given by the number (its third argument). The
final argument is the text where the port is connected –
characters written to the port go to the end of the editor.
The colors argument, if provided, specifies a list of
reduction-name/color-list pairs. The traces gui will color arrows
drawn because of the given reduction name with the given color instead
of using the default color.
The cdr of each of the elements of colors is a list
of colors, organized in pairs. The first two colors cover the colors
of the line and the border around the arrow head, the first when the
mouse is over a graph node that is connected to that arrow, and the
second for when the mouse is not over that arrow. Similarly, the next
colors are for the text drawn on the arrow and the last two are for
the color that fills the arrow head. If fewer than six colors are
specified, the specified colors are used and then defaults are
filled in for the remaining colors.
The racket-colors? argument (along with scheme-colors?,
retained for backward compatibility), controls the coloring of
each window. When racket-colors? is #t (and
scheme-colors? is #t too), traces colors the
contents according to DrRacket’s Racket-mode color scheme; otherwise,
traces uses a black color scheme.
The term-filter function is called each time a new node is
about to be inserted into the graph. If the filter returns false, the
node is not inserted into the graph.
The x-spacing and y-spacing control the amount of
space put between the snips in the default layout.
The layout argument is called (with all of the terms) when
new terms are inserted into the window. In general, it is called
after new terms are inserted in response to the user clicking on the
reduce button, and after the initial set of terms is inserted.
See also term-node-set-position!.
If edge-labels? is #t (the default), then edge labels
are drawn; otherwise not.
The edge-label-font argument is used as the font on the edge
labels. If #f is suppled, the dc<%> object’s default
font is used.
The traces library uses an instance of the mrlib/graph
library’s graph-pasteboard<%> interface to layout
the graphs. Sometimes, overriding one of its methods can
help give finer-grained control over the layout, so the
graph-pasteboard-mixin is applied to the class
before it is instantiated. Also note that all of the snips
inserted into the editor by this library have a
get-term-node method which returns the snip’s
This function behaves just like the function traces
instead of opening a window to show the reduction graph, it just saves
the reduction graph to the specified file
All of the arguments behave like the arguments to traces,
with the exception of the post-process argument. It is called
just before the PostScript is created with the graph pasteboard.
This function opens a stepper window for exploring the
behavior of the term t in the reduction system given by
The pp argument is the same as to the
traces function but is here for
backwards compatibility only and
should not be changed for most uses, but instead adjusted with
pretty-print-parameters. Specifically, the
highlighting shown in the stepper window can be wrong if
default-pretty-printer does not print sufficiently similarly
to how pretty-print prints (when adjusted by
pretty-print-parameters’s behavior, of course).
, this function opens a stepper window, but it
seeds it with the reduction-sequence supplied in seed
Returns a list of the children (ie, terms that this term
reduces to) of the given node.
Note that this function does not return all terms that this
term reduces to – only those that are currently in the
Returns a list of the parents (ie, terms that reduced to the
current term) of the given node.
Note that this function does not return all terms that
reduce to this one – only those that are currently in the
Returns a list of the names of the reductions that led to
the given node, in the same order as the result of
term-node-parents. If the list contains #f, that means that
the corresponding step does not have a label.
Changes the highlighting of the node; if its second argument
, the coloring is removed, otherwise the color is set
to the specified color%
object or the color named by the
string. The color-database<%>
is used to convert the string
to a color%
Changes the highlighting of the node; if its second argument
is #t, the term is colored pink, if it is #f, the term is
not colored specially.
Returns the expression in this node.
Sets the position of tn in the graph to (x,y).
Returns the x coordinate of tn in the window.
Returns the y coordinate of tn in the window.
Returns the width of tn in the window.
Returns the height of tn in the window.
Recognizes term nodes.
A parameter that controls how many steps the traces
takes before stopping.
A parameter that controls the initial font size for the terms shown
in the GUI window.
A parameter that determines the initial width of the boxes
where terms are displayed (measured in characters) for both
the stepper and traces.
If its value is a number, then the number is used as the width for
every term. If its value is a function, then the function is called
with each term and the resulting number is used as the width.
These six parameters control the color of the edges in the graph.
The dark colors are used when the mouse is over one of the nodes that
is connected to this edge. The light colors are used when it isn’t.
The pen colors control the color of the line. The brush colors control
the color used to fill the arrowhead and the text colors control the
color used to draw the label on the edge.
A parameter that is used to set other pretty-print
Specifically, whenever default-pretty-printer prints
something it calls f with a thunk that does the actual
printing. Thus, f can adjust pretty-print’s
parameters to adjust how printing happens.
This function uses the value of pretty-print-parameters to adjust how it prints.
It sets the pretty-print-columns parameter to
width, and it sets pretty-print-size-hook
and pretty-print-print-hook to print holes and the
symbol 'hole to match the way they are input in a