326 lines
11 KiB
Racket
326 lines
11 KiB
Racket
#lang scribble/doc
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@(require scribble/manual
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scribble/struct
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scribble/eval
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(for-label scheme/base
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macro-debugger/expand
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macro-debugger/stepper
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macro-debugger/stepper-text
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macro-debugger/syntax-browser
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(rename-in scheme (free-identifier=? module-identifier=?))))
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@(define the-eval
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(let ([the-eval (make-base-eval)])
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(the-eval '(require macro-debugger/expand
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macro-debugger/stepper-text))
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the-eval))
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@title{@bold{Macro Debugger}}
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@author["Ryan Culpepper"]
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The macro-debugger collection contains two tools: a stepper for macro
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expansion and a standalone syntax browser. The macro stepper shows the
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programmer the expansion of a program as a sequence of rewriting
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steps, using the syntax browser to display the individual terms. The
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syntax browser uses colors and a properties panel to show the term's
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syntax properties, such as lexical binding information and source
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location.
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@section{Macro stepper}
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@defmodule[macro-debugger/stepper]
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@defproc[(expand/step [stx any/c])
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(is-a/c macro-stepper<%>)]{
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Expands the syntax (or S-expression) and opens a macro stepper frame
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for stepping through the expansion.
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}
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@definterface[macro-stepper<%> ()]{
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@defmethod[(at-start?) boolean?]
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@defmethod[(at-end?) boolean?]
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@defmethod[(navigate-to-start) void?]
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@defmethod[(navigate-to-end) void?]
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@defmethod[(navigate-previous) void?]
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@defmethod[(navigate-next) void?]
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@defmethod[(at-top?) boolean?]
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@defmethod[(at-bottom?) boolean?]
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@defmethod[(navigate-up) void?]
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@defmethod[(navigate-down) void?]
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}
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@section{Macro expansion tools}
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@defmodule[macro-debugger/expand]
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This module provides @scheme[expand]-like procedures that allow the
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user to specify macros whose expansions should be hidden.
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Warning: because of limitations in the way macro expansion is
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selectively hidden, the resulting syntax may not evaluate to the same
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thing as the original syntax.
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@defproc[(expand-only [stx any/c] [transparent-macros (listof identifier?)])
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syntax?]{
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Expands the given syntax @scheme[stx], but only shows the expansion
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of macros whose names occur in @scheme[transparent-macros].
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@(examples #:eval the-eval
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(syntax->datum
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(expand-only #'(let ([x 1] [y 2]) (or (even? x) (even? y)))
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(list #'or))))
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}
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@defproc[(expand/hide [stx any/c] [hidden-macros (listof identifier?)])
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syntax?]{
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Expands the given syntax @scheme[stx], but hides the expansion of macros in the
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given identifier list (conceptually, the complement of expand-only).
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@(examples #:eval the-eval
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(syntax->datum
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(expand/hide #'(let ([x 1] [y 2]) (or (even? x) (even? y)))
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(list #'or))))
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}
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@defproc[(expand/show-predicate [stx any/c] [show? (-> identifier? boolean?)])
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syntax?]{
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Expands the given syntax @scheme[stx], but only shows the expansion of macros
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whose names satisfy the predicate @scheme[show?].
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@(examples #:eval the-eval
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(syntax->datum
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(expand/show-predicate
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#'(let ([x 1] [y 2]) (or (even? x) (even? y)))
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(lambda (id) (memq (syntax-e id) '(or #%app))))))
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}
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@section{Macro stepper text interface}
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@defmodule[macro-debugger/stepper-text]
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@defproc[(expand/step-text [stx any/c]
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[show? (or/c (-> identifier? boolean?)
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(listof identifier?))
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(lambda (x) #t)])
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void?]{
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Expands the syntax and prints the macro expansion steps. If the
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identifier predicate is given, it determines which macros are shown
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(if absent, all macros are shown). A list of identifiers is also
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accepted.
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@(examples #:eval the-eval
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(expand/step-text #'(let ([x 1] [y 2]) (or (even? x) (even? y)))
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(list #'or))
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#;(expand/step-text #'(let ([x 1]) (even? x)))
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#;(expand/step-text #'(let ([x 1] [y 2]) (or (even? x) (even? y)))
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(lambda (id) (eq? (syntax-e id) 'or))))
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}
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@defproc[(stepper-text [stx any/c]
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[show? (or/c (-> identifier? boolean?)
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(listof identifier?))
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(lambda (x) #t)])
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(symbol? -> void?)]{
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Returns a procedure that can be called on the symbol
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@scheme['next] to print the next step or on the symbol
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@scheme['all] to print out all remaining steps.
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}
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@section{Syntax browser}
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@defmodule[macro-debugger/syntax-browser]
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@defproc[(browse-syntax [stx syntax?])
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void?]{
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Creates a frame with the given syntax object shown. More information
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on using the GUI is available below.
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}
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@defproc[(browse-syntaxes [stxs (listof syntax?)])
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void?]{
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Like @scheme[browse-syntax], but shows multiple syntax objects in
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the same frame. The coloring partitions are shared between the two,
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showing the relationships between subterms in different syntax
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objects.
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}
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@;{
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@defproc[(syntax-snip [stx syntax?])
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(is-a/c snip%)]{
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Like @scheme[browse-syntax], but creates a snip that can be
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displayed in an editor.
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}
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}
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@section{Using the macro stepper}
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@subsection{Navigation}
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The stepper presents expansion as a linear sequence of rewriting
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process, and it gives the user controls to step forward or backwards
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as well as to jump to the beginning or end of the expansion process.
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If the macro stepper is showing multiple expansions, then it also
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provides "Previous term" and "Next term" buttons to go up and down in
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the list of expansions. Horizontal lines delimit the current expansion
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from the others.
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@subsection{Macro hiding}
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Macro hiding lets one see how expansion would look if certain macros
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were actually primitive syntactic forms. The macro stepper skips over
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the expansion of the macros you designate as opaque, but it still
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shows the expansion of their subterms.
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The bottom panel of the macro stepper controls the macro hiding
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policy. The user changes the policy by selecting an identifier in the
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syntax browser pane and then clicking one of "Hide module", "Hide
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macro", or "Show macro". The new rule appears in the policy display,
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and the user may later remove it using the "Delete" button.
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The stepper also offers coarser-grained options that can hide
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collections of modules at once. These options have lower precedence
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than the rules above.
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Macro hiding, even with no macros marked opaque, also hides certain
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other kinds of steps: internal defines are not rewritten to letrecs,
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begin forms are not spliced into module or block bodies, etc.
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@section{Using the syntax browser}
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@subsection{Selection (bold)}
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The user can click on any part of a subterm to select it. To select a
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parenthesized subterm, click on either of the parentheses. The
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selected syntax is bolded. Since one syntax object may occur inside of
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multiple other syntax objects, clicking on one occurrence will cause
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all occurrences to be bolded.
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The syntax browser displays information about the selected syntax
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object in the properties panel on the right, when that panel is
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shown. The selected syntax also determines the highlighting done by
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the secondary partitioning (see below).
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@subsection{Primary partition (foreground color)}
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The primary partitioning always assigns two syntax subterms the same
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color if they have the same marks. In the absence of unhygienic
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macros, this means that subterms with the same foreground color were
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either present in the original pre-expansion syntax or generated by
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the same macro transformation step.
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Syntax colored in black always corresponds to unmarked syntax. Such
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syntax may be original, or it may be produced by the expansion of a
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nonhygienic macro.
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@subsection{Secondary partitioning (highlight)}
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The user may select a *secondary partitioning* from a drop-down box
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(or in the macro stepper, through the Syntax menu). This partitioning
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applies only to identifiers. When the user selects an identifier, all
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terms in the same equivalence class as the selected term are
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highlighted in yellow.
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The available secondary partitionings are:
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@itemize{
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@item{@scheme[bound-identifier=?]}
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@item{@scheme[module-identifier=?]}
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@item{@scheme[module-or-top-identifier=?]}
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@item{@bold{symbolic-identifier=?}:
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Two identifiers are symbolic-identifier=? if discarding all lexical
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context information yields the same symbol.
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}
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@item{@bold{same marks}:
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Two identifiers have the same marks if (barring nonhygienic macros)
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they were produced by the same macro transformation step.
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}
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@item{@bold{same source module}:
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The bindings of the two identifiers come from definitions in the
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same module.
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}
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@item{@bold{same nominal module}:
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The bindings of the two identifiers were imported into the current
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context by requiring the same module.
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}
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}
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@subsection{Properties}
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When the properties pane is shown, it displays properties of the
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selected syntax object. The properties pane has three tabbed pages:
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- Binding
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If the selection is an identifier, shows the binding information
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associated with the syntax object.
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*Note: See the warning in the section below.
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For more information, look up 'identifier-binding',
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'identifier-transformer-binding', and
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'identifier-template-binding' in the Help Desk.
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- Source
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Displays source location information about the syntax object.
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- Properties
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Displays properties (see 'syntax-property') of the selection
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when it has properties it knows the keys for.
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@subsection{Warnings about interpreting syntax}
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The binding information of a *syntax object* may not be the same as
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the binding structure of the *program* it represents. The binding
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structure of a *program* is only determined after macro expansion is
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complete.
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For example, in @schemeblock[(browse-syntax #'(lambda (foo) foo))]
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the syntax browser will report that the inner 'foo' is unbound, even
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though in the *program* that this syntax represents, the inner 'foo'
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is bound to the outer 'foo'.
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@subsection{Notes and Limitations}
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The syntax browser does not have a way of extending the set of
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available secondary partitions.
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The syntax browser does not have a way of extending the set of known
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properties.
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The syntax browser does not preserve the distinction between
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parentheses and square brackets.
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@section{Notes for DrScheme language implementors}
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The macro stepper works "out of the box" only with certain languages
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out of all the languages available from the DrScheme languages
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menu. For example, the macro stepper is disabled for the teaching
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languages.
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An implementor of a new DrScheme language can designate their language
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"macro-steppable" by overriding the 'enable-macro-stepper?' method of
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their implementation of 'drscheme:language:language<%>'. The default
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implementation in the mixin provided by
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'drscheme:language:get-default-mixin' returns false; override this
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method to return true if the macro stepper button should be shown for
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this language.
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Note: There is currently no way to customize the behavior of the macro
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stepper for different languages. When enabled, the macro stepper sees
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exactly those terms that pass through the 'current-eval' handler.
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