13.5 Writing (original) (raw)

13.5 Writing🔗ℹ

Writes datum to out, normally in such a way that instances of core datatypes can be read back in. If out has a handler associated to it via port-write-handler, then the handler is called. Otherwise, the default printer is used (inwrite mode), as configured by various parameters.

See The Printer for more information about the default printer. In particular, note that write may require memory proportional to the depth of the value being printed, due to the initial cycle check.

Examples:

Displays datum to out, similar to write, but usually in such a way that byte- and character-based datatypes are written as raw bytes or characters. If out has a handler associated to it via port-display-handler, then the handler is called. Otherwise, the default printer is used (in displaymode), as configured by various parameters.

See The Printer for more information about the default printer. In particular, note that display may require memory proportional to the depth of the value being printed, due to the initial cycle check.

Prints datum to out. If out has a handler associated to it via port-print-handler, then the handler is called. Otherwise, the handler specified byglobal-port-print-handler is called; the default handler uses the default printer in print mode.

The optional quote-depth argument adjusts printing when theprint-as-expression parameter is set to #t. In that case, quote-depth specifies the starting quote depth for printing datum.

The rationale for providing print is that displayand write both have specific output conventions, and those conventions restrict the ways that an environment can change the behavior of display and write procedures. No output conventions should be assumed for print, so that environments are free to modify the actual output generated by print in any way.

The same as (write datum out) followed by (newline out).

Added in version 6.1.1.8 of package base.

The same as (display datum out) followed by (newline out), which is similar to println in Pascal or Java.

The same as (print datum out quote-depth) followed by(newline out).

The println function is not equivalent to println in other languages, because println uses printing conventions that are closer to write than to display. For a closer analog to println in other languages, use displayln.

Added in version 6.1.1.8 of package base.

Prints formatted output to out, where form is a string that is printed directly, except for special formatting escapes:

• ~n or ~% prints a newline character (which is equivalent to \n in a literal format string)
• ~a or ~A displays the next argument among the vs
• ~s or ~S writes the next argument among the vs
• ~v or ~V prints the next argument among the vs
• ~.‹c› where ‹c› is a,A, s, S, v, or V: truncates default-handler display, write, or print output to (error-print-width) characters, using ... as the last three characters if the untruncated output would be longer
• ~e or ~E outputs the next argument among thevs using the current error value conversion handler (seeerror-value->string-handler) and current error printing width
• ~c or ~C write-chars the next argument in vs; if the next argument is not a character, the exn:fail:contract exception is raised
• ~b or ~B prints the next argument among thevs in binary; if the next argument is not an exact number, theexn:fail:contract exception is raised
• ~o or ~O prints the next argument among thevs in octal; if the next argument is not an exact number, theexn:fail:contract exception is raised
• ~x or ~X prints the next argument among thevs in hexadecimal; if the next argument is not an exact number, the exn:fail:contract exception is raised
• ~~ prints a tilde.
• ~‹w›, where ‹w› is a whitespace character (see char-whitespace?), skips characters inform until a non-whitespace character is encountered or until a second end-of-line is encountered (whichever happens first). On all platforms, an end-of-line can be #\return,#\newline, or #\return followed immediately by#\newline.

The form string must not contain any ~ that is not one of the above escapes, otherwise theexn:fail:contract exception is raised. When the format string requires morevs than are supplied, theexn:fail:contract exception is raised. Similarly, when more vs are supplied than are used by the format string, theexn:fail:contract exception is raised.

Example:

(3 4) as a string is "(3 4)".

Formats to a string. The result is the same as

Example:

> (format "~a as a string is ~s.\n" '(3 4) "(3 4)")
"(3 4) as a string is \"(3 4)\".\n"

A parameter that controls pair printing. If the value is true, then pairs print using { and } instead of( and ). The default is #f.

A parameter that controls pair printing. If the value is true, then mutable pairs print using { and } instead of( and ). The default is #t.

A parameter that enables or disablesprint and write of values that have noreadable form (using the default reader), including structures that have a custom-write procedure (seeprop:custom-write), but not including uninternedsymbols and unreadable symbols (which print the same asinterned symbols). If the parameter value is #f, an attempt to print an unreadable value raises exn:fail. The parameter value defaults to #t. See The Printer for more information.

A parameter that controls printing data with sharing; defaults to#f. See The Printer for more information.

A parameter that controls printing structure values in vector orprefab form; defaults to #t. See The Printerfor more information. This parameter has no effect on the printing of structures that have a custom-write procedure (seeprop:custom-write).

A parameter that controls printing box values; defaults to#t. See Printing Boxes for more information.

A parameter that controls printing vectors; defaults to#f. See Printing Vectors for more information.

A parameter that controls printing of booleans. When the parameter’s value is true, #t and #f print as #trueand #false, otherwise they print as #tand #f. The default is #f.

A parameter that controls printing of two-element lists that start with quote, 'quasiquote, 'unquote,'unquote-splicing, 'syntax, 'quasisyntax,'unsyntax, or 'unsyntax-splicing; defaults to#f. See Printing Pairs and Lists for more information.

A parameter that controls printing in print mode (as opposed to write or display); defaults to #t. SeeThe Printer for more information.

A parameter that controls printing of syntax objects. Up towidth characters are used to show the datum form of a syntax object within #<syntax...> (after thesyntax object’s source location, if any), where ... is used as the last three characters if the printed form would otherwise be longer than width characters. A value of 0 forwidth means that the datum is not shown at all.

A parameter that contains a recommendation for the number of columns that should be used for printing values via print. May or may not be respected by print - the current default handler for print does not. It is expected that REPLs that use some form of pretty-printing for values respect this parameter.

Added in version 8.0.0.13 of package base.

A parameter that is used when writing compiled code (see Printing Compiled Code) that contains pathname literals, including source-location pathnames for procedure names. When the parameter’s value is a path, paths that syntactically extend pathare converted to relative paths; when the resulting compiled code is read, relative paths are converted back to complete paths using the current-load-relative-directory parameter (if it is not #f; otherwise, the path is left relative). When the parameter’s value is (cons rel-to-path base-path), then paths that syntactically extend base-path are converted as relative to rel-to-path; the rel-to-path must extend base-path, in which case 'uppath elements (in the sense of build-path) may be used to make a path relative to rel-to-path.

Gets or sets the port write handler, port display handler, or port print handler for out. This handler is called to output to the port when write,display, or print (respectively) is applied to the port. Each handler must accept two arguments: the value to be printed and the destination port. The handler’s return value is ignored.

A port print handler optionally accepts a third argument, which corresponds to the optional third argument to print; if a procedure given to port-print-handler does not accept a third argument, it is wrapped with a procedure that discards the optional third argument.

The default port display and write handlers print Racket expressions with Racket’s built-in printer (see The Printer). The default print handler calls the global port print handler (the value of the global-port-print-handler parameter); the default global port print handler is the same as the default write handler.

A parameter that determines global port print handler, which is called by the default port print handler (seeport-print-handler) to print values into a port. The default value is equivalent to default-global-port-print-handler.

A global port print handler optionally accepts a third argument, which corresponds to the optional third argument toprint. If a procedure given toglobal-port-print-handler does not accept a third argument, it is wrapped with a procedure that discards the optional third argument.

Prints v to out using the built-in printer (seeThe Printer) in print mode.

Added in version 8.8.0.6 of package base.