1Format(3) OCaml library Format(3)
2
6 Format - Pretty-printing.
7
9 Module Format
10
12 Module Format
13 : sig end
14 Pretty-printing.
17 This module implements a pretty-printing facility to format values
19 within Format.boxes and Format.tags combined with a set of Format.fpp .
20 The pretty-printer splits lines at specified Format.breaks , and in‐
21 dents lines according to the box structure. Similarly, Format.tags can
22 be used to decouple text presentation from its contents.
23 This pretty-printing facility is implemented as an overlay on top of
25 abstract Format.formatter which provide basic output functions. Some
26 formatters are predefined, notably:
27 - Format.std_formatter outputs to stdout
29 - Format.err_formatter outputs to stderr
32 Most functions in the Format module come in two variants: a short ver‐
34 sion that operates on Format.std_formatter and the generic version pre‐
35 fixed by pp_ that takes a formatter as its first argument.
36 More formatters can be created with Format.formatter_of_out_channel ,
38 Format.formatter_of_buffer , Format.formatter_of_symbolic_output_buffer
39 or using Format.formatter .
40 Introduction
48 For a gentle introduction to the basics of pretty-printing using Format
49 , read http://caml.inria.fr/resources/doc/guides/format.en.html.
50 You may consider this module as providing an extension to the printf
52 facility to provide automatic line splitting. The addition of
53 pretty-printing annotations to your regular printf format strings gives
54 you fancy indentation and line breaks. Pretty-printing annotations are
55 described below in the documentation of the function Format.fprintf .
56 You may also use the explicit pretty-printing box management and print‐
58 ing functions provided by this module. This style is more basic but
59 more verbose than the concise fprintf format strings.
60 For instance, the sequence open_box 0; print_string "x ="; print_space
62 ();
63 print_int 1; close_box (); print_newline () that prints x = 1
64 within a pretty-printing box, can be abbreviated as printf "@[%s@
65 %i@]@." "x =" 1 , or even shorter printf "@[x =@ %i@]@." 1 .
66 Rule of thumb for casual users of this library:
68 -use simple pretty-printing boxes (as obtained by open_box 0 );
70 -use simple break hints as obtained by print_cut () that outputs a sim‐
72 ple break hint, or by print_space () that outputs a space indicating a
73 break hint;
74 -once a pretty-printing box is open, display its material with basic
76 printing functions (e. g. print_int and print_string );
77 -when the material for a pretty-printing box has been printed, call
79 close_box () to close the box;
80 -at the end of pretty-printing, flush the pretty-printer to display all
82 the remaining material, e.g. evaluate print_newline () .
83 The behavior of pretty-printing commands is unspecified if there is no
85 open pretty-printing box. Each box opened by one of the open_ functions
86 below must be closed using close_box for proper formatting. Otherwise,
87 some of the material printed in the boxes may not be output, or may be
88 formatted incorrectly.
89 In case of interactive use, each phrase is executed in the initial
91 state of the standard pretty-printer: after each phrase execution, the
92 interactive system closes all open pretty-printing boxes, flushes all
93 pending text, and resets the standard pretty-printer.
94 Warning: mixing calls to pretty-printing functions of this module with
96 calls to Stdlib low level output functions is error prone.
97 The pretty-printing functions output material that is delayed in the
99 pretty-printer queue and stacks in order to compute proper line split‐
100 ting. In contrast, basic I/O output functions write directly in their
101 output device. As a consequence, the output of a basic I/O function may
102 appear before the output of a pretty-printing function that has been
103 called before. For instance,
104 Stdlib.print_string "<";
105 Format.print_string "PRETTY";
106 Stdlib.print_string ">";
107 Format.print_string "TEXT";
108 leads to output <>PRETTYTEXT .
109 type formatter
111 Abstract data corresponding to a pretty-printer (also called a format‐
114 ter) and all its machinery. See also Format.formatter .
115 Pretty-printing boxes
120 The pretty-printing engine uses the concepts of pretty-printing box and
121 break hint to drive indentation and line splitting behavior of the
122 pretty-printer.
123 Each different pretty-printing box kind introduces a specific line
125 splitting policy:
126 -within an horizontal box, break hints never split the line (but the
129 line may be split in a box nested deeper),
130 -within a vertical box, break hints always split the line,
132 -within an horizontal/vertical box, if the box fits on the current line
134 then break hints never split the line, otherwise break hint always
135 split the line,
136 -within a compacting box, a break hint never splits the line, unless
138 there is no more room on the current line.
139 Note that line splitting policy is box specific: the policy of a box
141 does not rule the policy of inner boxes. For instance, if a vertical
142 box is nested in an horizontal box, all break hints within the vertical
143 box will split the line.
144 Moreover, opening a box after the Format.maxindent splits the line
146 whether or not the box would end up fitting on the line.
147 val pp_open_box : formatter -> int -> unit
149 val open_box : int -> unit
154 pp_open_box ppf d opens a new compacting pretty-printing box with off‐
157 set d in the formatter ppf .
158 Within this box, the pretty-printer prints as much as possible material
160 on every line.
161 A break hint splits the line if there is no more room on the line to
163 print the remainder of the box.
164 Within this box, the pretty-printer emphasizes the box structure: if a
166 structural box does not fit fully on a simple line, a break hint also
167 splits the line if the splitting ``moves to the left'' (i.e. the new
168 line gets an indentation smaller than the one of the current line).
169 This box is the general purpose pretty-printing box.
171 If the pretty-printer splits the line in the box, offset d is added to
173 the current indentation.
174 val pp_close_box : formatter -> unit -> unit
178 val close_box : unit -> unit
183 Closes the most recently open pretty-printing box.
185 val pp_open_hbox : formatter -> unit -> unit
189 val open_hbox : unit -> unit
194 pp_open_hbox ppf () opens a new 'horizontal' pretty-printing box.
197 This box prints material on a single line.
199 Break hints in a horizontal box never split the line. (Line splitting
201 may still occur inside boxes nested deeper).
202 val pp_open_vbox : formatter -> int -> unit
206 val open_vbox : int -> unit
211 pp_open_vbox ppf d opens a new 'vertical' pretty-printing box with off‐
214 set d .
215 This box prints material on as many lines as break hints in the box.
217 Every break hint in a vertical box splits the line.
219 If the pretty-printer splits the line in the box, d is added to the
221 current indentation.
222 val pp_open_hvbox : formatter -> int -> unit
226 val open_hvbox : int -> unit
231 pp_open_hvbox ppf d opens a new 'horizontal/vertical' pretty-printing
234 box with offset d .
235 This box behaves as an horizontal box if it fits on a single line, oth‐
237 erwise it behaves as a vertical box.
238 If the pretty-printer splits the line in the box, d is added to the
240 current indentation.
241 val pp_open_hovbox : formatter -> int -> unit
245 val open_hovbox : int -> unit
250 pp_open_hovbox ppf d opens a new 'horizontal-or-vertical' pretty-print‐
253 ing box with offset d .
254 This box prints material as much as possible on every line.
256 A break hint splits the line if there is no more room on the line to
258 print the remainder of the box.
259 If the pretty-printer splits the line in the box, d is added to the
261 current indentation.
262 Formatting functions
267 val pp_print_string : formatter -> string -> unit
268 val print_string : string -> unit
273 pp_print_string ppf s prints s in the current pretty-printing box.
276 val pp_print_as : formatter -> int -> string -> unit
280 val print_as : int -> string -> unit
285 pp_print_as ppf len s prints s in the current pretty-printing box. The
288 pretty-printer formats s as if it were of length len .
289 val pp_print_int : formatter -> int -> unit
293 val print_int : int -> unit
298 Print an integer in the current pretty-printing box.
300 val pp_print_float : formatter -> float -> unit
304 val print_float : float -> unit
309 Print a floating point number in the current pretty-printing box.
311 val pp_print_char : formatter -> char -> unit
315 val print_char : char -> unit
320 Print a character in the current pretty-printing box.
322 val pp_print_bool : formatter -> bool -> unit
326 val print_bool : bool -> unit
331 Print a boolean in the current pretty-printing box.
333 Break hints
338 A 'break hint' tells the pretty-printer to output some space or split
339 the line whichever way is more appropriate to the current pretty-print‐
340 ing box splitting rules.
341 Break hints are used to separate printing items and are mandatory to
343 let the pretty-printer correctly split lines and indent items.
344 Simple break hints are:
346 -the 'space': output a space or split the line if appropriate,
348 -the 'cut': split the line if appropriate.
350 Note: the notions of space and line splitting are abstract for the
352 pretty-printing engine, since those notions can be completely redefined
353 by the programmer. However, in the pretty-printer default setting,
354 ``output a space'' simply means printing a space character (ASCII code
355 32) and ``split the line'' means printing a newline character (ASCII
356 code 10).
357 val pp_print_space : formatter -> unit -> unit
359 val print_space : unit -> unit
364 pp_print_space ppf () emits a 'space' break hint: the pretty-printer
367 may split the line at this point, otherwise it prints one space.
368 pp_print_space ppf () is equivalent to pp_print_break ppf 1 0 .
371 val pp_print_cut : formatter -> unit -> unit
375 val print_cut : unit -> unit
380 pp_print_cut ppf () emits a 'cut' break hint: the pretty-printer may
383 split the line at this point, otherwise it prints nothing.
384 pp_print_cut ppf () is equivalent to pp_print_break ppf 0 0 .
387 val pp_print_break : formatter -> int -> int -> unit
391 val print_break : int -> int -> unit
396 pp_print_break ppf nspaces offset emits a 'full' break hint: the
399 pretty-printer may split the line at this point, otherwise it prints
400 nspaces spaces.
401 If the pretty-printer splits the line, offset is added to the current
403 indentation.
404 val pp_print_custom_break : formatter -> fits:string * int * string ->
408 breaks:string * int * string -> unit
409 pp_print_custom_break ppf ~fits:(s1, n, s2) ~breaks:(s3, m, s4) emits a
412 custom break hint: the pretty-printer may split the line at this point.
413 If it does not split the line, then the s1 is emitted, then n spaces,
415 then s2 .
416 If it splits the line, then it emits the s3 string, then an indent (ac‐
418 cording to the box rules), then an offset of m spaces, then the s4
419 string.
420 While n and m are handled by formatter_out_functions.out_indent , the
422 strings will be handled by formatter_out_functions.out_string . This
423 allows for a custom formatter that handles indentation distinctly, for
424 example, outputs <br/> tags or entities.
425 The custom break is useful if you want to change which visible
427 (non-whitespace) characters are printed in case of break or no break.
428 For example, when printing a list
429 [a; b; c]
430 trailing semicolon when it is printed vertically:
431 [
434 a;
435 b;
436 c;
437 ]
438 You can do this as follows:
441 printf "@[<v 0>[@;<0 2>@[<v 0>a;@,b;@,c@]%t]@]@\n"
442 (pp_print_custom_break ~fits:("", 0, "") ~breaks:(";", 0, ""))
443 Since 4.08.0
447 val pp_force_newline : formatter -> unit -> unit
451 val force_newline : unit -> unit
456 Force a new line in the current pretty-printing box.
458 The pretty-printer must split the line at this point,
460 Not the normal way of pretty-printing, since imperative line splitting
462 may interfere with current line counters and box size calculation. Us‐
463 ing break hints within an enclosing vertical box is a better alterna‐
464 tive.
465 val pp_print_if_newline : formatter -> unit -> unit
469 val print_if_newline : unit -> unit
474 Execute the next formatting command if the preceding line has just been
476 split. Otherwise, ignore the next formatting command.
477 Pretty-printing termination
482 val pp_print_flush : formatter -> unit -> unit
483 val print_flush : unit -> unit
488 End of pretty-printing: resets the pretty-printer to initial state.
490 All open pretty-printing boxes are closed, all pending text is printed.
492 In addition, the pretty-printer low level output device is flushed to
493 ensure that all pending text is really displayed.
494 Note: never use print_flush in the normal course of a pretty-printing
496 routine, since the pretty-printer uses a complex buffering machinery to
497 properly indent the output; manually flushing those buffers at random
498 would conflict with the pretty-printer strategy and result to poor ren‐
499 dering.
500 Only consider using print_flush when displaying all pending material is
502 mandatory (for instance in case of interactive use when you want the
503 user to read some text) and when resetting the pretty-printer state
504 will not disturb further pretty-printing.
505 Warning: If the output device of the pretty-printer is an output chan‐
507 nel, repeated calls to print_flush means repeated calls to flush to
508 flush the out channel; these explicit flush calls could foil the
509 buffering strategy of output channels and could dramatically impact ef‐
510 ficiency.
511 val pp_print_newline : formatter -> unit -> unit
515 val print_newline : unit -> unit
520 End of pretty-printing: resets the pretty-printer to initial state.
522 All open pretty-printing boxes are closed, all pending text is printed.
524 Equivalent to Format.print_flush followed by a new line. See corre‐
526 sponding words of caution for Format.print_flush .
527 Note: this is not the normal way to output a new line; the preferred
529 method is using break hints within a vertical pretty-printing box.
530 Margin
535 val pp_set_margin : formatter -> int -> unit
536 val set_margin : int -> unit
541 pp_set_margin ppf d sets the right margin to d (in characters): the
544 pretty-printer splits lines that overflow the right margin according to
545 the break hints given. Setting the margin to d means that the format‐
546 ting engine aims at printing at most d-1 characters per line. Nothing
547 happens if d is smaller than 2. If d is too large, the right margin is
548 set to the maximum admissible value (which is greater than 10 ^ 9 ).
549 If d is less than the current maximum indentation limit, the maximum
550 indentation limit is decreased while trying to preserve a minimal ratio
551 max_indent/margin>=50% and if possible the current difference margin -
552 max_indent .
553 See also Format.pp_set_geometry .
555 val pp_get_margin : formatter -> unit -> int
559 val get_margin : unit -> int
564 Returns the position of the right margin.
566 Maximum indentation limit
571 val pp_set_max_indent : formatter -> int -> unit
572 val set_max_indent : int -> unit
577 pp_set_max_indent ppf d sets the maximum indentation limit of lines to
580 d (in characters): once this limit is reached, new pretty-printing
581 boxes are rejected to the left, unless the enclosing box fully fits on
582 the current line. As an illustration,
583 set_margin 10; set_max_indent 5; printf "@[123456@[7@]89A@]@."
584 yields
585 123456
586 789A
587 because the nested box "@[7@]" is opened after the maximum indentation
589 limit ( 7>5 ) and its parent box does not fit on the current line. Ei‐
590 ther decreasing the length of the parent box to make it fit on a line:
591 printf "@[123456@[7@]89@]@."
592 or opening an intermediary box before the maximum indentation limit
593 which fits on the current line
594 printf "@[123@[456@[7@]89@]A@]@."
595 avoids the rejection to the left of the inner boxes and print respec‐
596 tively "123456789" and "123456789A" . Note also that vertical boxes
597 never fit on a line whereas horizontal boxes always fully fit on the
598 current line. Opening a box may split a line whereas the contents may
599 have fit. If this behavior is problematic, it can be curtailed by set‐
600 ting the maximum indentation limit to margin - 1 . Note that setting
601 the maximum indentation limit to margin is invalid.
602 Nothing happens if d is smaller than 2.
604 If d is too large, the limit is set to the maximum admissible value
606 (which is greater than 10 ^ 9 ).
607 If d is greater or equal than the current margin, it is ignored, and
609 the current maximum indentation limit is kept.
610 See also Format.pp_set_geometry .
612 val pp_get_max_indent : formatter -> unit -> int
616 val get_max_indent : unit -> int
621 Return the maximum indentation limit (in characters).
623 Geometry
628 Geometric functions can be used to manipulate simultaneously the cou‐
629 pled variables, margin and maxixum indentation limit.
630 type geometry = {
632 max_indent : int ;
633 margin : int ;
634 }
635 val check_geometry : geometry -> bool
641 Check if the formatter geometry is valid: 1 < max_indent < margin
643 val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
648 val set_geometry : max_indent:int -> margin:int -> unit
653 val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int ->
658 unit
659 val safe_set_geometry : max_indent:int -> margin:int -> unit
664 pp_set_geometry ppf ~max_indent ~margin sets both the margin and maxi‐
667 mum indentation limit for ppf .
668 When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin
670 is equivalent to pp_set_margin ppf margin; pp_set_max_indent ppf
671 max_indent ; and avoids the subtly incorrect pp_set_max_indent ppf
672 max_indent; pp_set_margin ppf margin ;
673 Outside of this domain, pp_set_geometry raises an invalid argument ex‐
675 ception whereas pp_safe_set_geometry does nothing.
676 Since 4.08.0
679 val pp_update_geometry : formatter -> (geometry -> geometry) -> unit
683 pp_update_geometry ppf (fun geo -> { geo with ... }) lets you update a
686 formatter's geometry in a way that is robust to extension of the geome‐
687 try record with new fields.
688 Raises an invalid argument exception if the returned geometry does not
690 satisfy Format.check_geometry .
691 Since 4.11.0
694 val update_geometry : (geometry -> geometry) -> unit
698 val pp_get_geometry : formatter -> unit -> geometry
703 val get_geometry : unit -> geometry
708 Return the current geometry of the formatter
710 Since 4.08.0
713 Maximum formatting depth
718 The maximum formatting depth is the maximum number of pretty-printing
719 boxes simultaneously open.
720 Material inside boxes nested deeper is printed as an ellipsis (more
722 precisely as the text returned by Format.get_ellipsis_text () ).
723 val pp_set_max_boxes : formatter -> int -> unit
725 val set_max_boxes : int -> unit
730 pp_set_max_boxes ppf max sets the maximum number of pretty-printing
733 boxes simultaneously open.
734 Material inside boxes nested deeper is printed as an ellipsis (more
736 precisely as the text returned by Format.get_ellipsis_text () ).
737 Nothing happens if max is smaller than 2.
739 val pp_get_max_boxes : formatter -> unit -> int
743 val get_max_boxes : unit -> int
748 Returns the maximum number of pretty-printing boxes allowed before el‐
750 lipsis.
751 val pp_over_max_boxes : formatter -> unit -> bool
755 val over_max_boxes : unit -> bool
760 Tests if the maximum number of pretty-printing boxes allowed have al‐
762 ready been opened.
763 Tabulation boxes
768 A tabulation box prints material on lines divided into cells of fixed
769 length. A tabulation box provides a simple way to display vertical col‐
770 umns of left adjusted text.
771 This box features command set_tab to define cell boundaries, and com‐
773 mand print_tab to move from cell to cell and split the line when there
774 is no more cells to print on the line.
775 Note: printing within tabulation box is line directed, so arbitrary
777 line splitting inside a tabulation box leads to poor rendering. Yet,
778 controlled use of tabulation boxes allows simple printing of columns
779 within module Format .
780 val pp_open_tbox : formatter -> unit -> unit
782 val open_tbox : unit -> unit
787 open_tbox () opens a new tabulation box.
790 This box prints lines separated into cells of fixed width.
792 Inside a tabulation box, special tabulation markers defines points of
794 interest on the line (for instance to delimit cell boundaries). Func‐
795 tion Format.set_tab sets a tabulation marker at insertion point.
796 A tabulation box features specific tabulation breaks to move to next
798 tabulation marker or split the line. Function Format.print_tbreak
799 prints a tabulation break.
800 val pp_close_tbox : formatter -> unit -> unit
804 val close_tbox : unit -> unit
809 Closes the most recently opened tabulation box.
811 val pp_set_tab : formatter -> unit -> unit
815 val set_tab : unit -> unit
820 Sets a tabulation marker at current insertion point.
822 val pp_print_tab : formatter -> unit -> unit
826 val print_tab : unit -> unit
831 print_tab () emits a 'next' tabulation break hint: if not already set
834 on a tabulation marker, the insertion point moves to the first tabula‐
835 tion marker on the right, or the pretty-printer splits the line and in‐
836 sertion point moves to the leftmost tabulation marker.
837 It is equivalent to print_tbreak 0 0 .
839 val pp_print_tbreak : formatter -> int -> int -> unit
843 val print_tbreak : int -> int -> unit
848 print_tbreak nspaces offset emits a 'full' tabulation break hint.
851 If not already set on a tabulation marker, the insertion point moves to
853 the first tabulation marker on the right and the pretty-printer prints
854 nspaces spaces.
855 If there is no next tabulation marker on the right, the pretty-printer
857 splits the line at this point, then insertion point moves to the left‐
858 most tabulation marker of the box.
859 If the pretty-printer splits the line, offset is added to the current
861 indentation.
862 Ellipsis
867 val pp_set_ellipsis_text : formatter -> string -> unit
868 val set_ellipsis_text : string -> unit
873 Set the text of the ellipsis printed when too many pretty-printing
875 boxes are open (a single dot, . , by default).
876 val pp_get_ellipsis_text : formatter -> unit -> string
880 val get_ellipsis_text : unit -> string
885 Return the text of the ellipsis.
887 Semantic tags
892 type stag = ..
893 Semantic tags (or simply tags) are user's defined annotations to asso‐
896 ciate user's specific operations to printed entities.
897 Common usage of semantic tags is text decoration to get specific font
899 or text size rendering for a display device, or marking delimitation of
900 entities (e.g. HTML or TeX elements or terminal escape sequences).
901 More sophisticated usage of semantic tags could handle dynamic modifi‐
902 cation of the pretty-printer behavior to properly print the material
903 within some specific tags. For instance, we can define an RGB tag like
904 so:
905 type stag += RGB of {r:int;g:int;b:int}
906 In order to properly delimit printed entities, a semantic tag must be
909 opened before and closed after the entity. Semantic tags must be prop‐
910 erly nested like parentheses using Format.pp_open_stag and For‐
911 mat.pp_close_stag .
912 Tag specific operations occur any time a tag is opened or closed, At
914 each occurrence, two kinds of operations are performed tag-marking and
915 tag-printing:
916 -The tag-marking operation is the simpler tag specific operation: it
918 simply writes a tag specific string into the output device of the for‐
919 matter. Tag-marking does not interfere with line-splitting computation.
920 -The tag-printing operation is the more involved tag specific opera‐
922 tion: it can print arbitrary material to the formatter. Tag-printing is
923 tightly linked to the current pretty-printer operations.
924 Roughly speaking, tag-marking is commonly used to get a better render‐
926 ing of texts in the rendering device, while tag-printing allows fine
927 tuning of printing routines to print the same entity differently ac‐
928 cording to the semantic tags (i.e. print additional material or even
929 omit parts of the output).
930 More precisely: when a semantic tag is opened or closed then both and
932 successive 'tag-printing' and 'tag-marking' operations occur:
933 -Tag-printing a semantic tag means calling the formatter specific func‐
935 tion print_open_stag (resp. print_close_stag ) with the name of the
936 tag as argument: that tag-printing function can then print any regular
937 material to the formatter (so that this material is enqueued as usual
938 in the formatter queue for further line splitting computation).
939 -Tag-marking a semantic tag means calling the formatter specific func‐
941 tion mark_open_stag (resp. mark_close_stag ) with the name of the tag
942 as argument: that tag-marking function can then return the 'tag-opening
943 marker' (resp. `tag-closing marker') for direct output into the output
944 device of the formatter.
945 Being written directly into the output device of the formatter, seman‐
947 tic tag marker strings are not considered as part of the printing mate‐
948 rial that drives line splitting (in other words, the length of the
949 strings corresponding to tag markers is considered as zero for line
950 splitting).
951 Thus, semantic tag handling is in some sense transparent to
953 pretty-printing and does not interfere with usual indentation. Hence, a
954 single pretty-printing routine can output both simple 'verbatim' mate‐
955 rial or richer decorated output depending on the treatment of tags. By
956 default, tags are not active, hence the output is not decorated with
957 tag information. Once set_tags is set to true , the pretty-printer en‐
958 gine honors tags and decorates the output accordingly.
959 Default tag-marking functions behave the HTML way: Format.tag are en‐
961 closed in "<" and ">" while other tags are ignored; hence, opening
962 marker for tag string "t" is "<t>" and closing marker is "</t>" .
963 Default tag-printing functions just do nothing.
965 Tag-marking and tag-printing functions are user definable and can be
967 set by calling Format.set_formatter_stag_functions .
968 Semantic tag operations may be set on or off with Format.set_tags .
970 Tag-marking operations may be set on or off with Format.set_mark_tags .
971 Tag-printing operations may be set on or off with Format.set_print_tags
972 .
973 type tag = string
976 type stag +=
981 | String_tag of tag (* String_tag s is a string tag s . String tags
982 can be inserted either by explicitly using the constructor String_tag
983 or by using the dedicated format syntax "@{<s> ... @}" .
984 *)
985 val pp_open_stag : formatter -> stag -> unit
991 val open_stag : stag -> unit
996 pp_open_stag ppf t opens the semantic tag named t .
999 The print_open_stag tag-printing function of the formatter is called
1001 with t as argument; then the opening tag marker for t , as given by
1002 mark_open_stag t , is written into the output device of the formatter.
1003 val pp_close_stag : formatter -> unit -> unit
1007 val close_stag : unit -> unit
1012 pp_close_stag ppf () closes the most recently opened semantic tag t .
1015 The closing tag marker, as given by mark_close_stag t , is written into
1017 the output device of the formatter; then the print_close_stag
1018 tag-printing function of the formatter is called with t as argument.
1019 val pp_set_tags : formatter -> bool -> unit
1023 val set_tags : bool -> unit
1028 pp_set_tags ppf b turns on or off the treatment of semantic tags (de‐
1031 fault is off).
1032 val pp_set_print_tags : formatter -> bool -> unit
1036 val set_print_tags : bool -> unit
1041 pp_set_print_tags ppf b turns on or off the tag-printing operations.
1044 val pp_set_mark_tags : formatter -> bool -> unit
1048 val set_mark_tags : bool -> unit
1053 pp_set_mark_tags ppf b turns on or off the tag-marking operations.
1056 val pp_get_print_tags : formatter -> unit -> bool
1060 val get_print_tags : unit -> bool
1065 Return the current status of tag-printing operations.
1067 val pp_get_mark_tags : formatter -> unit -> bool
1071 val get_mark_tags : unit -> bool
1076 Return the current status of tag-marking operations.
1078 val pp_set_formatter_out_channel : formatter -> out_channel -> unit
1082 Redirecting the standard formatter output
1085 val set_formatter_out_channel : out_channel -> unit
1086 Redirect the standard pretty-printer output to the given channel. (All
1088 the output functions of the standard formatter are set to the default
1089 output functions printing to the given channel.)
1090 set_formatter_out_channel is equivalent to Format.pp_set_format‐
1093 ter_out_channel std_formatter .
1094 val pp_set_formatter_output_functions : formatter -> (string -> int ->
1098 int -> unit) -> (unit -> unit) -> unit
1099 val set_formatter_output_functions : (string -> int -> int -> unit) ->
1104 (unit -> unit) -> unit
1105 pp_set_formatter_output_functions ppf out flush redirects the standard
1108 pretty-printer output functions to the functions out and flush .
1109 The out function performs all the pretty-printer string output. It is
1111 called with a string s , a start position p , and a number of charac‐
1112 ters n ; it is supposed to output characters p to p + n - 1 of s .
1113 The flush function is called whenever the pretty-printer is flushed
1115 (via conversion %! , or pretty-printing indications @? or @. , or
1116 using low level functions print_flush or print_newline ).
1117 val pp_get_formatter_output_functions : formatter -> unit -> (string ->
1121 int -> int -> unit) * (unit -> unit)
1122 val get_formatter_output_functions : unit -> (string -> int -> int ->
1127 unit) * (unit -> unit)
1128 Return the current output functions of the standard pretty-printer.
1130 Redefining formatter output
1135 The Format module is versatile enough to let you completely redefine
1136 the meaning of pretty-printing output: you may provide your own func‐
1137 tions to define how to handle indentation, line splitting, and even
1138 printing of all the characters that have to be printed!
1139 Redefining output functions
1141 type formatter_out_functions = {
1142 out_string : string -> int -> int -> unit ;
1143 out_flush : unit -> unit ;
1144 out_newline : unit -> unit ;
1145 out_spaces : int -> unit ;
1146 out_indent : int -> unit ;
1147 }
1148 The set of output functions specific to a formatter:
1151 -the out_string function performs all the pretty-printer string output.
1153 It is called with a string s , a start position p , and a number of
1154 characters n ; it is supposed to output characters p to p + n - 1 of s
1155 .
1156 -the out_flush function flushes the pretty-printer output device.
1158 - out_newline is called to open a new line when the pretty-printer
1160 splits the line.
1161 -the out_spaces function outputs spaces when a break hint leads to spa‐
1163 ces instead of a line split. It is called with the number of spaces to
1164 output.
1165 -the out_indent function performs new line indentation when the
1167 pretty-printer splits the line. It is called with the indentation value
1168 of the new line.
1169 By default:
1171 -fields out_string and out_flush are output device specific; (e.g.
1173 output_string and flush for a out_channel device, or Buffer.add_sub‐
1174 string and ignore for a Buffer.t output device),
1175 -field out_newline is equivalent to out_string "\n" 0 1 ;
1177 -fields out_spaces and out_indent are equivalent to out_string
1179 (String.make n ' ') 0 n .
1180 Since 4.01.0
1184 val pp_set_formatter_out_functions : formatter -> formatter_out_func‐
1188 tions -> unit
1189 val set_formatter_out_functions : formatter_out_functions -> unit
1194 pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer
1197 output functions of ppf to those of argument out_funs ,
1198 This way, you can change the meaning of indentation (which can be some‐
1200 thing else than just printing space characters) and the meaning of new
1201 lines opening (which can be connected to any other action needed by the
1202 application at hand).
1203 Reasonable defaults for functions out_spaces and out_newline are re‐
1205 spectively out_funs.out_string (String.make n ' ') 0 n and
1206 out_funs.out_string "\n" 0 1 .
1207 Since 4.01.0
1210 val pp_get_formatter_out_functions : formatter -> unit -> format‐
1214 ter_out_functions
1215 val get_formatter_out_functions : unit -> formatter_out_functions
1220 Return the current output functions of the pretty-printer, including
1222 line splitting and indentation functions. Useful to record the current
1223 setting and restore it afterwards.
1224 Since 4.01.0
1227 Redefining semantic tag operations
1232 type formatter_stag_functions = {
1233 mark_open_stag : stag -> string ;
1234 mark_close_stag : stag -> string ;
1235 print_open_stag : stag -> unit ;
1236 print_close_stag : stag -> unit ;
1237 }
1238 The semantic tag handling functions specific to a formatter: mark ver‐
1241 sions are the 'tag-marking' functions that associate a string marker to
1242 a tag in order for the pretty-printing engine to write those markers as
1243 0 length tokens in the output device of the formatter. print versions
1244 are the 'tag-printing' functions that can perform regular printing when
1245 a tag is closed or opened.
1246 val pp_set_formatter_stag_functions : formatter -> formatter_stag_func‐
1250 tions -> unit
1251 val set_formatter_stag_functions : formatter_stag_functions -> unit
1256 pp_set_formatter_stag_functions ppf tag_funs changes the meaning of
1259 opening and closing semantic tag operations to use the functions in
1260 tag_funs when printing on ppf .
1261 When opening a semantic tag with name t , the string t is passed to the
1263 opening tag-marking function (the mark_open_stag field of the record
1264 tag_funs ), that must return the opening tag marker for that name. When
1265 the next call to close_stag () happens, the semantic tag name t is sent
1266 back to the closing tag-marking function (the mark_close_stag field of
1267 record tag_funs ), that must return a closing tag marker for that name.
1268 The print_ field of the record contains the tag-printing functions that
1270 are called at tag opening and tag closing time, to output regular mate‐
1271 rial in the pretty-printer queue.
1272 val pp_get_formatter_stag_functions : formatter -> unit -> format‐
1276 ter_stag_functions
1277 val get_formatter_stag_functions : unit -> formatter_stag_functions
1282 Return the current semantic tag operation functions of the standard
1284 pretty-printer.
1285 Defining formatters
1290 Defining new formatters permits unrelated output of material in paral‐
1291 lel on several output devices. All the parameters of a formatter are
1292 local to the formatter: right margin, maximum indentation limit, maxi‐
1293 mum number of pretty-printing boxes simultaneously open, ellipsis, and
1294 so on, are specific to each formatter and may be fixed independently.
1295 For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b
1297 returns a new formatter using buffer b as its output device. Simi‐
1298 larly, given a out_channel output channel oc , Format.format‐
1299 ter_of_out_channel oc returns a new formatter using channel oc as its
1300 output device.
1301 Alternatively, given out_funs , a complete set of output functions for
1303 a formatter, then Format.formatter_of_out_functions out_funs computes a
1304 new formatter using those functions for output.
1305 val formatter_of_out_channel : out_channel -> formatter
1307 formatter_of_out_channel oc returns a new formatter writing to the cor‐
1310 responding output channel oc .
1311 val std_formatter : formatter
1315 The standard formatter to write to standard output.
1317 It is defined as Format.formatter_of_out_channel stdout .
1319 val err_formatter : formatter
1323 A formatter to write to standard error.
1325 It is defined as Format.formatter_of_out_channel stderr .
1327 val formatter_of_buffer : Buffer.t -> formatter
1331 formatter_of_buffer b returns a new formatter writing to buffer b . At
1334 the end of pretty-printing, the formatter must be flushed using For‐
1335 mat.pp_print_flush or Format.pp_print_newline , to print all the pend‐
1336 ing material into the buffer.
1337 val stdbuf : Buffer.t
1341 The string buffer in which str_formatter writes.
1343 val str_formatter : formatter
1347 A formatter to output to the Format.stdbuf string buffer.
1349 str_formatter is defined as Format.formatter_of_buffer Format.stdbuf .
1352 val flush_str_formatter : unit -> string
1356 Returns the material printed with str_formatter , flushes the formatter
1358 and resets the corresponding buffer.
1359 val make_formatter : (string -> int -> int -> unit) -> (unit -> unit)
1363 -> formatter
1364 make_formatter out flush returns a new formatter that outputs with
1367 function out , and flushes with function flush .
1368 For instance,
1370 make_formatter
1371 (Stdlib.output oc)
1372 (fun () -> Stdlib.flush oc)
1373 returns a formatter to the out_channel oc .
1374 val formatter_of_out_functions : formatter_out_functions -> formatter
1378 formatter_of_out_functions out_funs returns a new formatter that writes
1381 with the set of output functions out_funs .
1382 See definition of type Format.formatter_out_functions for the meaning
1384 of argument out_funs .
1385 Since 4.06.0
1388 Symbolic pretty-printing
1393 Symbolic pretty-printing is pretty-printing using a symbolic formatter,
1394 i.e. a formatter that outputs symbolic pretty-printing items.
1395 When using a symbolic formatter, all regular pretty-printing activities
1397 occur but output material is symbolic and stored in a buffer of output
1398 items. At the end of pretty-printing, flushing the output buffer al‐
1399 lows post-processing of symbolic output before performing low level
1400 output operations.
1401 In practice, first define a symbolic output buffer b using:
1403 - let sob = make_symbolic_output_buffer () . Then define a symbolic
1405 formatter with:
1406 - let ppf = formatter_of_symbolic_output_buffer sob
1408 Use symbolic formatter ppf as usual, and retrieve symbolic items at end
1410 of pretty-printing by flushing symbolic output buffer sob with:
1411 - flush_symbolic_output_buffer sob .
1413 type symbolic_output_item =
1416 | Output_flush (* symbolic flush command
1417 *)
1418 | Output_newline (* symbolic newline command
1419 *)
1420 | Output_string of string
1421 (* Output_string s : symbolic output for string s
1422 *)
1424 | Output_spaces of int
1425 (* Output_spaces n : symbolic command to output n spaces
1426 *)
1427 | Output_indent of int
1428 (* Output_indent i : symbolic indentation of size i
1429 *)
1431 Items produced by symbolic pretty-printers
1434 Since 4.06.0
1437 type symbolic_output_buffer
1440 The output buffer of a symbolic pretty-printer.
1443 Since 4.06.0
1446 val make_symbolic_output_buffer : unit -> symbolic_output_buffer
1450 make_symbolic_output_buffer () returns a fresh buffer for symbolic out‐
1453 put.
1454 Since 4.06.0
1457 val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
1461 clear_symbolic_output_buffer sob resets buffer sob .
1464 Since 4.06.0
1467 val get_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1471 bolic_output_item list
1472 get_symbolic_output_buffer sob returns the contents of buffer sob .
1475 Since 4.06.0
1478 val flush_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1482 bolic_output_item list
1483 flush_symbolic_output_buffer sob returns the contents of buffer sob and
1486 resets buffer sob . flush_symbolic_output_buffer sob is equivalent to
1487 let items = get_symbolic_output_buffer sob in
1488 clear_symbolic_output_buffer sob; items
1489 Since 4.06.0
1493 val add_symbolic_output_item : symbolic_output_buffer -> symbolic_out‐
1497 put_item -> unit
1498 add_symbolic_output_item sob itm adds item itm to buffer sob .
1501 Since 4.06.0
1504 val formatter_of_symbolic_output_buffer : symbolic_output_buffer ->
1508 formatter
1509 formatter_of_symbolic_output_buffer sob returns a symbolic formatter
1512 that outputs to symbolic_output_buffer sob .
1513 Since 4.06.0
1516 Convenience formatting functions.
1521 val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter
1522 -> 'a -> unit) -> formatter -> 'a list -> unit
1523 pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to
1526 print each item, and calling pp_sep between items ( pp_sep defaults to
1527 Format.pp_print_cut . Does nothing on empty lists.
1528 Since 4.02.0
1531 val pp_print_text : formatter -> string -> unit
1535 pp_print_text ppf s prints s with spaces and newlines respectively
1538 printed using Format.pp_print_space and Format.pp_force_newline .
1539 Since 4.02.0
1542 val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter
1546 -> 'a -> unit) -> formatter -> 'a option -> unit
1547 pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is
1550 Some v and none if it is None . none prints nothing by default.
1551 Since 4.08
1554 val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter
1558 -> 'e -> unit) -> formatter -> ('a, 'e) result -> unit
1559 pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _
1562 and error if r is Error _ .
1563 Since 4.08
1566 Formatted pretty-printing
1571 Module Format provides a complete set of printf like functions for
1572 pretty-printing using format string specifications.
1573 Specific annotations may be added in the format strings to give
1575 pretty-printing commands to the pretty-printing engine.
1576 Those annotations are introduced in the format strings using the @
1578 character. For instance, @ means a space break, @, means a cut, @[
1579 opens a new box, and @] closes the last open box.
1580 val fprintf : formatter -> ('a, formatter, unit) format -> 'a
1582 fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN accord‐
1588 ing to the format string fmt , and outputs the resulting string on the
1589 formatter ff .
1590 The format string fmt is a character string which contains three types
1592 of objects: plain characters and conversion specifications as specified
1593 in the Printf module, and pretty-printing indications specific to the
1594 Format module.
1595 The pretty-printing indication characters are introduced by a @ charac‐
1597 ter, and their meanings are:
1598 - @[ : open a pretty-printing box. The type and offset of the box may
1600 be optionally specified with the following syntax: the < character,
1601 followed by an optional box type indication, then an optional integer
1602 offset, and the closing > character. Pretty-printing box type is one
1603 of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
1604 pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box,
1605 ' hv ' stands for an 'horizontal/vertical' pretty-printing box, ' b '
1606 stands for an 'horizontal-or-vertical' pretty-printing box demonstrat‐
1607 ing indentation, ' hov ' stands a simple 'horizontal-or-vertical'
1608 pretty-printing box. For instance, @[<hov 2> opens an 'horizon‐
1609 tal-or-vertical' pretty-printing box with indentation 2 as obtained
1610 with open_hovbox 2 . For more details about pretty-printing boxes, see
1611 the various box opening functions open_*box .
1612 - @] : close the most recently opened pretty-printing box.
1614 - @, : output a 'cut' break hint, as with print_cut () .
1616 - @ : output a 'space' break hint, as with print_space () .
1618 - @; : output a 'full' break hint as with print_break . The nspaces and
1620 offset parameters of the break hint may be optionally specified with
1621 the following syntax: the < character, followed by an integer nspaces
1622 value, then an integer offset , and a closing > character. If no pa‐
1623 rameters are provided, the good break defaults to a 'space' break hint.
1624 - @. : flush the pretty-printer and split the line, as with print_new‐
1626 line () .
1627 - @<n> : print the following item as if it were of length n . Hence,
1629 printf "@<0>%s" arg prints arg as a zero length string. If @<n> is not
1630 followed by a conversion specification, then the following character of
1631 the format is printed as if it were of length n .
1632 - @{ : open a semantic tag. The name of the tag may be optionally spec‐
1634 ified with the following syntax: the < character, followed by an op‐
1635 tional string specification, and the closing > character. The string
1636 specification is any character string that does not contain the closing
1637 character '>' . If omitted, the tag name defaults to the empty string.
1638 For more details about semantic tags, see the functions For‐
1639 mat.open_stag and Format.close_stag .
1640 - @} : close the most recently opened semantic tag.
1642 - @? : flush the pretty-printer as with print_flush () . This is
1644 equivalent to the conversion %! .
1645 - @\n : force a newline, as with force_newline () , not the normal way
1647 of pretty-printing, you should prefer using break hints inside a verti‐
1648 cal pretty-printing box.
1649 Note: To prevent the interpretation of a @ character as a pretty-print‐
1651 ing indication, escape it with a % character. Old quotation mode @@ is
1652 deprecated since it is not compatible with formatted input interpreta‐
1653 tion of character '@' .
1654 Example: printf "@[%s@ %d@]@." "x =" 1 is equivalent to open_box ();
1656 print_string "x ="; print_space ();
1657 print_int 1; close_box (); print_newline () . It prints x = 1
1658 within a pretty-printing 'horizontal-or-vertical' box.
1659 val printf : ('a, formatter, unit) format -> 'a
1661 Same as fprintf above, but output on std_formatter .
1663 val eprintf : ('a, formatter, unit) format -> 'a
1667 Same as fprintf above, but output on err_formatter .
1669 val sprintf : ('a, unit, string) format -> 'a
1673 Same as printf above, but instead of printing on a formatter, returns a
1675 string containing the result of formatting the arguments. Note that
1676 the pretty-printer queue is flushed at the end of each call to sprintf
1677 .
1678 In case of multiple and related calls to sprintf to output material on
1680 a single string, you should consider using fprintf with the predefined
1681 formatter str_formatter and call flush_str_formatter () to get the fi‐
1682 nal result.
1683 Alternatively, you can use Format.fprintf with a formatter writing to a
1685 buffer of your own: flushing the formatter and the buffer at the end of
1686 pretty-printing returns the desired string.
1687 val asprintf : ('a, formatter, unit, string) format4 -> 'a
1691 Same as printf above, but instead of printing on a formatter, returns a
1693 string containing the result of formatting the arguments. The type of
1694 asprintf is general enough to interact nicely with %a conversions.
1695 Since 4.01.0
1698 val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
1702 Same as Format.fprintf , except the formatter is the last argument.
1704 dprintf "..." a b c is a function of type formatter -> unit which can
1705 be given to a format specifier %t .
1706 This can be used as a replacement for Format.asprintf to delay format‐
1708 ting decisions. Using the string returned by Format.asprintf in a for‐
1709 matting context forces formatting decisions to be taken in isolation,
1710 and the final string may be created prematurely. Format.dprintf allows
1711 delay of formatting decisions until the final formatting context is
1712 known. For example:
1713 let t = Format.dprintf "%i@ %i@ %i" 1 2 3 in
1714 ...
1715 Format.printf "@[<v>%t@]" t
1716 Since 4.08.0
1720 val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
1724 Same as fprintf above, but does not print anything. Useful to ignore
1726 some material when conditionally printing.
1727 Since 3.10.0
1730 Formatted Pretty-Printing with continuations.
1735 val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1737 'a) format4 -> 'b
1738 Same as fprintf above, but instead of returning immediately, passes the
1740 formatter to its first argument at the end of printing.
1741 val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a)
1745 format4 -> 'b
1746 Same as Format.dprintf above, but instead of returning immediately,
1748 passes the suspended printer to its first argument at the end of print‐
1749 ing.
1750 Since 4.08.0
1753 val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1757 'a) format4 -> 'b
1758 Same as kfprintf above, but does not print anything. Useful to ignore
1760 some material when conditionally printing.
1761 Since 3.12.0
1764 val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1768 Same as sprintf above, but instead of returning the string, passes it
1770 to the first argument.
1771 val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 ->
1775 'b
1776 Same as asprintf above, but instead of returning the string, passes it
1778 to the first argument.
1779 Since 4.03
1782 Deprecated
1787 val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
1788 Deprecated. This function is error prone. Do not use it. This func‐
1790 tion is neither compositional nor incremental, since it flushes the
1791 pretty-printer queue at each call.
1792 If you need to print to some buffer b , you must first define a format‐
1794 ter writing to b , using let to_b = formatter_of_buffer b ; then use
1795 regular calls to Format.fprintf with formatter to_b .
1796 val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1800 Deprecated. An alias for ksprintf .
1802 val set_all_formatter_output_functions : out:(string -> int -> int ->
1806 unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int
1807 -> unit) -> unit
1808 Deprecated. Subsumed by set_formatter_out_functions .
1810 val get_all_formatter_output_functions : unit -> (string -> int -> int
1814 -> unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
1815 Deprecated. Subsumed by get_formatter_out_functions .
1817 val pp_set_all_formatter_output_functions : formatter -> out:(string ->
1821 int -> int -> unit) -> flush:(unit -> unit) -> newline:(unit -> unit)
1822 -> spaces:(int -> unit) -> unit
1823 Deprecated. Subsumed by pp_set_formatter_out_functions .
1825 val pp_get_all_formatter_output_functions : formatter -> unit ->
1829 (string -> int -> int -> unit) * (unit -> unit) * (unit -> unit) * (int
1830 -> unit)
1831 Deprecated. Subsumed by pp_get_formatter_out_functions .
1833 String tags
1838 val pp_open_tag : formatter -> tag -> unit
1839 Deprecated. Subsumed by Format.pp_open_stag .
1841 val open_tag : tag -> unit
1845 Deprecated. Subsumed by Format.open_stag .
1847 val pp_close_tag : formatter -> unit -> unit
1851 Deprecated. Subsumed by Format.pp_close_stag .
1853 val close_tag : unit -> unit
1857 Deprecated. Subsumed by Format.close_stag .
1859 type formatter_tag_functions = {
1862 mark_open_tag : tag -> string ;
1863 mark_close_tag : tag -> string ;
1864 print_open_tag : tag -> unit ;
1865 print_close_tag : tag -> unit ;
1866 }
1867 Deprecated. Subsumed by Format.formatter_stag_functions .
1870 val pp_set_formatter_tag_functions : formatter -> formatter_tag_func‐
1874 tions -> unit
1875 Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
1877 This function will erase non-string tag formatting functions.
1880 val set_formatter_tag_functions : formatter_tag_functions -> unit
1884 Deprecated. Subsumed by Format.set_formatter_stag_functions .
1886 val pp_get_formatter_tag_functions : formatter -> unit -> format‐
1890 ter_tag_functions
1891 Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
1893 val get_formatter_tag_functions : unit -> formatter_tag_functions
1897 Deprecated. Subsumed by Format.get_formatter_stag_functions .
1899OCamldoc 2021-01-26 Format(3)