4 Typesetting Racket Code

Beware that if you use read-syntax on a file port, you may have to turn on line counting via port-count-lines! for the code to typeset properly. Also beware that when a source file containing a syntax or quote-syntax form is compiled, source location information is omitted from the compiled syntax object.

Normally, typeset-code is used through the code syntactic form, which works properly with compilation, and that escapes to pict-producing code via unsyntax. See also define-code.

Embedded picts within stx are used directly. Row elements are combined using and operator like htl-append, so use code-align (see below) as necessary to add an ascent to ascentless picts. More precisely, creation of a line of code uses pict-last to determine the end point of the element most recently added to a line; the main effect is that closing parentheses are attached in the right place when a multi-line pict is embedded in stx.

An identifier that starts with _ is italicized in the pict, and the _ is dropped, unless the code-italic-underscore-enabled parameter is set to #f. Also, unless code-scripts-enabled is set to #f, _ and ^ in the middle of a word create superscripts and subscripts, respectively (like TeX); for example foo^4_ok is displayed as the identifier foo with a 4 superscript and an ok subscript.

Further, uses of certain identifiers in stx typeset specially:

• code:blank — produces a space.

• (code:comment s ...) — produces a comment block, with each s on its own line, where each s must be a string or a pict.

• (code:line datum ...) — typesets the datum sequence, which is mostly useful for the top-level sequence, since typeset-code accepts only one argument.

• (code:contract datum ...) — like code:line, but every datum is colored as a comment, and a ; is prefixed to every line.

• (code:template datum ...) — like code:line, but a ; is prefixed to every line.

• $ — typesets as a vertical bar (for no particularly good reason).

For more information, see typeset-code and define-code, since code is defined as

  (define-code code typeset-code)

  (lambda (s) (text s (current-code-font) (current-font-size)))

This procedure is not used to typeset subscripts or other items that require font changes, where current-code-font is used directly.

The resulting code-id syntactic form takes a sequence of datums:

  (code-id datum ...)

It produces a pict that typesets the sequence. Source-location information for the datum determines the layout of code in the resulting pict. The code-id is expanded in such a way that source location is preserved during compilation (so typeset-code-id receives a syntax object with source locations intact).

If a datum contains (escape-id expr)—perhaps as #,expr when escape-id is unsyntax—then the expr is evaluated and the result datum is spliced in place of the escape-id form in datum. If the result is not a syntax object, it is given the source location of the escape-id form. A pict value intected this way as a datum is rendered as itself.

Meanwhile, runnable-id is bound to a syntax object that wraps the datums in a begin. In this case, _s are removed from the datums, but not the following expression. Thus, an _ identifier is used to comment out an expression from the pict, but have it present in the syntax object for evaluation.

The string-id is bound to a string representation of the code that is in the pict. This string is useful for copying to the clipboard with (send the-clipboard set-clipboard-string string-id 0).