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
21 indents lines according to the box structure. Similarly, Format.tags
22 can 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 (); print_int 1; close_box (); print_newline () that prints x = 1
63 within a pretty-printing box, can be abbreviated as printf @[%s@ %i@]@.
64 x = 1 , or even shorter printf @[x =@ %i@]@. 1 .
65 Rule of thumb for casual users of this library:
67 -use simple pretty-printing boxes (as obtained by open_box 0 );
69 -use simple break hints as obtained by print_cut () that outputs a sim‐
71 ple break hint, or by print_space () that outputs a space indicating a
72 break hint;
73 -once a pretty-printing box is open, display its material with basic
75 printing functions (e. g. print_int and print_string );
76 -when the material for a pretty-printing box has been printed, call
78 close_box () to close the box;
79 -at the end of pretty-printing, flush the pretty-printer to display all
81 the remaining material, e.g. evaluate print_newline () .
82 The behavior of pretty-printing commands is unspecified if there is no
84 open pretty-printing box. Each box opened by one of the open_ functions
85 below must be closed using close_box for proper formatting. Otherwise,
86 some of the material printed in the boxes may not be output, or may be
87 formatted incorrectly.
88 In case of interactive use, each phrase is executed in the initial
90 state of the standard pretty-printer: after each phrase execution, the
91 interactive system closes all open pretty-printing boxes, flushes all
92 pending text, and resets the standard pretty-printer.
93 Warning: mixing calls to pretty-printing functions of this module with
95 calls to Stdlib low level output functions is error prone.
96 The pretty-printing functions output material that is delayed in the
98 pretty-printer queue and stacks in order to compute proper line split‐
99 ting. In contrast, basic I/O output functions write directly in their
100 output device. As a consequence, the output of a basic I/O function may
101 appear before the output of a pretty-printing function that has been
102 called before. For instance, Stdlib.print_string < ; For‐
103 mat.print_string PRETTY ; Stdlib.print_string > ; Format.print_string
104 TEXT ; leads to output <>PRETTYTEXT .
105 type formatter
107 Abstract data corresponding to a pretty-printer (also called a format‐
110 ter) and all its machinery. See also Format.formatter .
111 Pretty-printing boxes
116 The pretty-printing engine uses the concepts of pretty-printing box and
117 break hint to drive indentation and line splitting behavior of the
118 pretty-printer.
119 Each different pretty-printing box kind introduces a specific line
121 splitting policy:
122 -within an horizontal box, break hints never split the line (but the
125 line may be split in a box nested deeper),
126 -within a vertical box, break hints always split the line,
128 -within an horizontal/vertical box, if the box fits on the current line
130 then break hints never split the line, otherwise break hint always
131 split the line,
132 -within a compacting box, a break hint never splits the line, unless
134 there is no more room on the current line.
135 Note that line splitting policy is box specific: the policy of a box
137 does not rule the policy of inner boxes. For instance, if a vertical
138 box is nested in an horizontal box, all break hints within the vertical
139 box will split the line.
140 val pp_open_box : formatter -> int -> unit
142 val open_box : int -> unit
147 pp_open_box ppf d opens a new compacting pretty-printing box with off‐
150 set d in the formatter ppf .
151 Within this box, the pretty-printer prints as much as possible material
153 on every line.
154 A break hint splits the line if there is no more room on the line to
156 print the remainder of the box.
157 Within this box, the pretty-printer emphasizes the box structure: a
159 break hint also splits the line if the splitting ``moves to the left''
160 (i.e. the new line gets an indentation smaller than the one of the cur‐
161 rent line).
162 This box is the general purpose pretty-printing box.
164 If the pretty-printer splits the line in the box, offset d is added to
166 the current indentation.
167 val pp_close_box : formatter -> unit -> unit
171 val close_box : unit -> unit
176 Closes the most recently open pretty-printing box.
178 val pp_open_hbox : formatter -> unit -> unit
182 val open_hbox : unit -> unit
187 pp_open_hbox ppf () opens a new 'horizontal' pretty-printing box.
190 This box prints material on a single line.
192 Break hints in a horizontal box never split the line. (Line splitting
194 may still occur inside boxes nested deeper).
195 val pp_open_vbox : formatter -> int -> unit
199 val open_vbox : int -> unit
204 pp_open_vbox ppf d opens a new 'vertical' pretty-printing box with off‐
207 set d .
208 This box prints material on as many lines as break hints in the box.
210 Every break hint in a vertical box splits the line.
212 If the pretty-printer splits the line in the box, d is added to the
214 current indentation.
215 val pp_open_hvbox : formatter -> int -> unit
219 val open_hvbox : int -> unit
224 pp_open_hvbox ppf d opens a new 'horizontal/vertical' pretty-printing
227 box with offset d .
228 This box behaves as an horizontal box if it fits on a single line, oth‐
230 erwise it behaves as a vertical box.
231 If the pretty-printer splits the line in the box, d is added to the
233 current indentation.
234 val pp_open_hovbox : formatter -> int -> unit
238 val open_hovbox : int -> unit
243 pp_open_hovbox ppf d opens a new 'horizontal-or-vertical' pretty-print‐
246 ing box with offset d .
247 This box prints material as much as possible on every line.
249 A break hint splits the line if there is no more room on the line to
251 print the remainder of the box.
252 If the pretty-printer splits the line in the box, d is added to the
254 current indentation.
255 Formatting functions
260 val pp_print_string : formatter -> string -> unit
261 val print_string : string -> unit
266 pp_print_string ppf s prints s in the current pretty-printing box.
269 val pp_print_as : formatter -> int -> string -> unit
273 val print_as : int -> string -> unit
278 pp_print_as ppf len s prints s in the current pretty-printing box. The
281 pretty-printer formats s as if it were of length len .
282 val pp_print_int : formatter -> int -> unit
286 val print_int : int -> unit
291 Print an integer in the current pretty-printing box.
293 val pp_print_float : formatter -> float -> unit
297 val print_float : float -> unit
302 Print a floating point number in the current pretty-printing box.
304 val pp_print_char : formatter -> char -> unit
308 val print_char : char -> unit
313 Print a character in the current pretty-printing box.
315 val pp_print_bool : formatter -> bool -> unit
319 val print_bool : bool -> unit
324 Print a boolean in the current pretty-printing box.
326 Break hints
331 A 'break hint' tells the pretty-printer to output some space or split
332 the line whichever way is more appropriate to the current pretty-print‐
333 ing box splitting rules.
334 Break hints are used to separate printing items and are mandatory to
336 let the pretty-printer correctly split lines and indent items.
337 Simple break hints are:
339 -the 'space': output a space or split the line if appropriate,
341 -the 'cut': split the line if appropriate.
343 Note: the notions of space and line splitting are abstract for the
345 pretty-printing engine, since those notions can be completely redefined
346 by the programmer. However, in the pretty-printer default setting,
347 ``output a space'' simply means printing a space character (ASCII code
348 32) and ``split the line'' means printing a newline character (ASCII
349 code 10).
350 val pp_print_space : formatter -> unit -> unit
352 val print_space : unit -> unit
357 pp_print_space ppf () emits a 'space' break hint: the pretty-printer
360 may split the line at this point, otherwise it prints one space.
361 pp_print_space ppf () is equivalent to pp_print_break ppf 1 0 .
364 val pp_print_cut : formatter -> unit -> unit
368 val print_cut : unit -> unit
373 pp_print_cut ppf () emits a 'cut' break hint: the pretty-printer may
376 split the line at this point, otherwise it prints nothing.
377 pp_print_cut ppf () is equivalent to pp_print_break ppf 0 0 .
380 val pp_print_break : formatter -> int -> int -> unit
384 val print_break : int -> int -> unit
389 pp_print_break ppf nspaces offset emits a 'full' break hint: the
392 pretty-printer may split the line at this point, otherwise it prints
393 nspaces spaces.
394 If the pretty-printer splits the line, offset is added to the current
396 indentation.
397 val pp_print_custom_break : formatter -> fits:string * int * string ->
401 breaks:string * int * string -> unit
402 pp_print_custom_break ppf ~fits:(s1, n, s2) ~breaks:(s3, m, s4) emits a
405 custom break hint: the pretty-printer may split the line at this point.
406 If it does not split the line, then the s1 is emitted, then n spaces,
408 then s2 .
409 If it splits the line, then it emits the s3 string, then an indent
411 (according to the box rules), then an offset of m spaces, then the s4
412 string.
413 While n and m are handled by formatter_out_functions.out_indent , the
415 strings will be handled by formatter_out_functions.out_string . This
416 allows for a custom formatter that handles indentation distinctly, for
417 example, outputs <br/> tags or entities.
418 The custom break is useful if you want to change which visible
420 (non-whitespace) characters are printed in case of break or no break.
421 For example, when printing a list [a; b; c] , you might want to add a
422 trailing semicolon when it is printed vertically:
423 [ a; b; c; ]
426 You can do this as follows: printf @[<v 0>[@;<0 2>@[<v
428 0>a;@,b;@,c@]%t]@]@\n (pp_print_custom_break ~fits:("", 0, )
429 ~breaks:(";", 0, ))
430 Since 4.08.0
434 val pp_force_newline : formatter -> unit -> unit
438 val force_newline : unit -> unit
443 Force a new line in the current pretty-printing box.
445 The pretty-printer must split the line at this point,
447 Not the normal way of pretty-printing, since imperative line splitting
449 may interfere with current line counters and box size calculation.
450 Using break hints within an enclosing vertical box is a better alterna‐
451 tive.
452 val pp_print_if_newline : formatter -> unit -> unit
456 val print_if_newline : unit -> unit
461 Execute the next formatting command if the preceding line has just been
463 split. Otherwise, ignore the next formatting command.
464 Pretty-printing termination
469 val pp_print_flush : formatter -> unit -> unit
470 val print_flush : unit -> unit
475 End of pretty-printing: resets the pretty-printer to initial state.
477 All open pretty-printing boxes are closed, all pending text is printed.
479 In addition, the pretty-printer low level output device is flushed to
480 ensure that all pending text is really displayed.
481 Note: never use print_flush in the normal course of a pretty-printing
483 routine, since the pretty-printer uses a complex buffering machinery to
484 properly indent the output; manually flushing those buffers at random
485 would conflict with the pretty-printer strategy and result to poor ren‐
486 dering.
487 Only consider using print_flush when displaying all pending material is
489 mandatory (for instance in case of interactive use when you want the
490 user to read some text) and when resetting the pretty-printer state
491 will not disturb further pretty-printing.
492 Warning: If the output device of the pretty-printer is an output chan‐
494 nel, repeated calls to print_flush means repeated calls to flush to
495 flush the out channel; these explicit flush calls could foil the
496 buffering strategy of output channels and could dramatically impact
497 efficiency.
498 val pp_print_newline : formatter -> unit -> unit
502 val print_newline : unit -> unit
507 End of pretty-printing: resets the pretty-printer to initial state.
509 All open pretty-printing boxes are closed, all pending text is printed.
511 Equivalent to Format.print_flush followed by a new line. See corre‐
513 sponding words of caution for Format.print_flush .
514 Note: this is not the normal way to output a new line; the preferred
516 method is using break hints within a vertical pretty-printing box.
517 Margin
522 val pp_set_margin : formatter -> int -> unit
523 val set_margin : int -> unit
528 pp_set_margin ppf d sets the right margin to d (in characters): the
531 pretty-printer splits lines that overflow the right margin according to
532 the break hints given. Nothing happens if d is smaller than 2. If d
533 is too large, the right margin is set to the maximum admissible value
534 (which is greater than 10 ^ 9 ). If d is less than the current maximum
535 indentation limit, the maximum indentation limit is decreased while
536 trying to preserve a minimal ratio max_indent/margin>=50% and if possi‐
537 ble the current difference margin - max_indent .
538 See also Format.pp_set_geometry .
540 val pp_get_margin : formatter -> unit -> int
544 val get_margin : unit -> int
549 Returns the position of the right margin.
551 Maximum indentation limit
556 val pp_set_max_indent : formatter -> int -> unit
557 val set_max_indent : int -> unit
562 pp_set_max_indent ppf d sets the maximum indentation limit of lines to
565 d (in characters): once this limit is reached, new pretty-printing
566 boxes are rejected to the left, unless the enclosing box fully fits on
567 the current line. As an illustration, set_margin 10; set_max_indent 5;
568 printf @[123456@[7@]89A@]@. yields 123456 789A because the nested box
569 @[7@] is opened after the maximum indentation limit ( 7>5 ) and its
570 parent box does not fit on the current line. Either decreasing the
571 length of the parent box to make it fit on a line: printf
572 @[123456@[7@]89@]@. or opening an intermediary box before the maximum
573 indentation limit which fits on the current line printf
574 @[123@[456@[7@]89@]A@]@. avoids the rejection to the left of the inner
575 boxes and print respectively 123456789 and 123456789A . Note also that
576 vertical boxes never fit on a line whereas horizontal boxes always
577 fully fit on the current line.
578 Nothing happens if d is smaller than 2.
580 If d is too large, the limit is set to the maximum admissible value
582 (which is greater than 10 ^ 9 ).
583 If d is greater or equal than the current margin, it is ignored, and
585 the current maximum indentation limit is kept.
586 See also Format.pp_set_geometry .
588 val pp_get_max_indent : formatter -> unit -> int
592 val get_max_indent : unit -> int
597 Return the maximum indentation limit (in characters).
599 Geometry
604 Geometric functions can be used to manipulate simultaneously the cou‐
605 pled variables, margin and maxixum indentation limit.
606 type geometry = {
608 max_indent : int ;
609 margin : int ;
610 }
611 val check_geometry : geometry -> bool
617 Check if the formatter geometry is valid: 1 < max_indent < margin
619 val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
624 val set_geometry : max_indent:int -> margin:int -> unit
629 val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int ->
634 unit
635 val safe_set_geometry : max_indent:int -> margin:int -> unit
640 pp_set_geometry ppf ~max_indent ~margin sets both the margin and maxi‐
643 mum indentation limit for ppf .
644 When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin
646 is equivalent to pp_set_margin ppf margin; pp_set_max_indent ppf
647 max_indent ; and avoids the subtly incorrect pp_set_max_indent ppf
648 max_indent; pp_set_margin ppf margin ;
649 Outside of this domain, pp_set_geometry raises an invalid argument
651 exception whereas pp_safe_set_geometry does nothing.
652 Since 4.08.0
655 val pp_get_geometry : formatter -> unit -> geometry
659 val get_geometry : unit -> geometry
664 Return the current geometry of the formatter
666 Since 4.08.0
669 Maximum formatting depth
674 The maximum formatting depth is the maximum number of pretty-printing
675 boxes simultaneously open.
676 Material inside boxes nested deeper is printed as an ellipsis (more
678 precisely as the text returned by Format.get_ellipsis_text () ).
679 val pp_set_max_boxes : formatter -> int -> unit
681 val set_max_boxes : int -> unit
686 pp_set_max_boxes ppf max sets the maximum number of pretty-printing
689 boxes simultaneously open.
690 Material inside boxes nested deeper is printed as an ellipsis (more
692 precisely as the text returned by Format.get_ellipsis_text () ).
693 Nothing happens if max is smaller than 2.
695 val pp_get_max_boxes : formatter -> unit -> int
699 val get_max_boxes : unit -> int
704 Returns the maximum number of pretty-printing boxes allowed before
706 ellipsis.
707 val pp_over_max_boxes : formatter -> unit -> bool
711 val over_max_boxes : unit -> bool
716 Tests if the maximum number of pretty-printing boxes allowed have
718 already been opened.
719 Tabulation boxes
724 A tabulation box prints material on lines divided into cells of fixed
725 length. A tabulation box provides a simple way to display vertical col‐
726 umns of left adjusted text.
727 This box features command set_tab to define cell boundaries, and com‐
729 mand print_tab to move from cell to cell and split the line when there
730 is no more cells to print on the line.
731 Note: printing within tabulation box is line directed, so arbitrary
733 line splitting inside a tabulation box leads to poor rendering. Yet,
734 controlled use of tabulation boxes allows simple printing of columns
735 within module Format .
736 val pp_open_tbox : formatter -> unit -> unit
738 val open_tbox : unit -> unit
743 open_tbox () opens a new tabulation box.
746 This box prints lines separated into cells of fixed width.
748 Inside a tabulation box, special tabulation markers defines points of
750 interest on the line (for instance to delimit cell boundaries). Func‐
751 tion Format.set_tab sets a tabulation marker at insertion point.
752 A tabulation box features specific tabulation breaks to move to next
754 tabulation marker or split the line. Function Format.print_tbreak
755 prints a tabulation break.
756 val pp_close_tbox : formatter -> unit -> unit
760 val close_tbox : unit -> unit
765 Closes the most recently opened tabulation box.
767 val pp_set_tab : formatter -> unit -> unit
771 val set_tab : unit -> unit
776 Sets a tabulation marker at current insertion point.
778 val pp_print_tab : formatter -> unit -> unit
782 val print_tab : unit -> unit
787 print_tab () emits a 'next' tabulation break hint: if not already set
790 on a tabulation marker, the insertion point moves to the first tabula‐
791 tion marker on the right, or the pretty-printer splits the line and
792 insertion point moves to the leftmost tabulation marker.
793 It is equivalent to print_tbreak 0 0 .
795 val pp_print_tbreak : formatter -> int -> int -> unit
799 val print_tbreak : int -> int -> unit
804 print_tbreak nspaces offset emits a 'full' tabulation break hint.
807 If not already set on a tabulation marker, the insertion point moves to
809 the first tabulation marker on the right and the pretty-printer prints
810 nspaces spaces.
811 If there is no next tabulation marker on the right, the pretty-printer
813 splits the line at this point, then insertion point moves to the left‐
814 most tabulation marker of the box.
815 If the pretty-printer splits the line, offset is added to the current
817 indentation.
818 Ellipsis
823 val pp_set_ellipsis_text : formatter -> string -> unit
824 val set_ellipsis_text : string -> unit
829 Set the text of the ellipsis printed when too many pretty-printing
831 boxes are open (a single dot, . , by default).
832 val pp_get_ellipsis_text : formatter -> unit -> string
836 val get_ellipsis_text : unit -> string
841 Return the text of the ellipsis.
843 Semantic tags
848 type stag = ..
849 Semantic tags (or simply tags) are user's defined annotations to asso‐
852 ciate user's specific operations to printed entities.
853 Common usage of semantic tags is text decoration to get specific font
855 or text size rendering for a display device, or marking delimitation of
856 entities (e.g. HTML or TeX elements or terminal escape sequences).
857 More sophisticated usage of semantic tags could handle dynamic modifi‐
858 cation of the pretty-printer behavior to properly print the material
859 within some specific tags. For instance, we can define an RGB tag like
860 so: type stag += RGB of {r:int;g:int;b:int}
861 In order to properly delimit printed entities, a semantic tag must be
863 opened before and closed after the entity. Semantic tags must be prop‐
864 erly nested like parentheses using Format.pp_open_stag and For‐
865 mat.pp_close_stag .
866 Tag specific operations occur any time a tag is opened or closed, At
868 each occurrence, two kinds of operations are performed tag-marking and
869 tag-printing:
870 -The tag-marking operation is the simpler tag specific operation: it
872 simply writes a tag specific string into the output device of the for‐
873 matter. Tag-marking does not interfere with line-splitting computation.
874 -The tag-printing operation is the more involved tag specific opera‐
876 tion: it can print arbitrary material to the formatter. Tag-printing is
877 tightly linked to the current pretty-printer operations.
878 Roughly speaking, tag-marking is commonly used to get a better render‐
880 ing of texts in the rendering device, while tag-printing allows fine
881 tuning of printing routines to print the same entity differently
882 according to the semantic tags (i.e. print additional material or even
883 omit parts of the output).
884 More precisely: when a semantic tag is opened or closed then both and
886 successive 'tag-printing' and 'tag-marking' operations occur:
887 -Tag-printing a semantic tag means calling the formatter specific func‐
889 tion print_open_stag (resp. print_close_stag ) with the name of the
890 tag as argument: that tag-printing function can then print any regular
891 material to the formatter (so that this material is enqueued as usual
892 in the formatter queue for further line splitting computation).
893 -Tag-marking a semantic tag means calling the formatter specific func‐
895 tion mark_open_stag (resp. mark_close_stag ) with the name of the tag
896 as argument: that tag-marking function can then return the 'tag-opening
897 marker' (resp. `tag-closing marker') for direct output into the output
898 device of the formatter.
899 Being written directly into the output device of the formatter, seman‐
901 tic tag marker strings are not considered as part of the printing mate‐
902 rial that drives line splitting (in other words, the length of the
903 strings corresponding to tag markers is considered as zero for line
904 splitting).
905 Thus, semantic tag handling is in some sense transparent to
907 pretty-printing and does not interfere with usual indentation. Hence, a
908 single pretty-printing routine can output both simple 'verbatim' mate‐
909 rial or richer decorated output depending on the treatment of tags. By
910 default, tags are not active, hence the output is not decorated with
911 tag information. Once set_tags is set to true , the pretty-printer
912 engine honors tags and decorates the output accordingly.
913 Default tag-marking functions behave the HTML way: Format.tag are
915 enclosed in "<" and ">" while other tags are ignored; hence, opening
916 marker for tag string t is <t> and closing marker is </t> .
917 Default tag-printing functions just do nothing.
919 Tag-marking and tag-printing functions are user definable and can be
921 set by calling Format.set_formatter_stag_functions .
922 Semantic tag operations may be set on or off with Format.set_tags .
924 Tag-marking operations may be set on or off with Format.set_mark_tags .
925 Tag-printing operations may be set on or off with Format.set_print_tags
926 .
927 type tag = string
930 type stag +=
935 | String_tag of tag (* String_tag s is a string tag s . String tags
936 can be inserted either by explicitly using the constructor String_tag
937 or by using the dedicated format syntax @{<s> ... @} .
938 *)
939 val pp_open_stag : formatter -> stag -> unit
945 val open_stag : stag -> unit
950 pp_open_stag ppf t opens the semantic tag named t .
953 The print_open_stag tag-printing function of the formatter is called
955 with t as argument; then the opening tag marker for t , as given by
956 mark_open_stag t , is written into the output device of the formatter.
957 val pp_close_stag : formatter -> unit -> unit
961 val close_stag : unit -> unit
966 pp_close_stag ppf () closes the most recently opened semantic tag t .
969 The closing tag marker, as given by mark_close_stag t , is written into
971 the output device of the formatter; then the print_close_stag
972 tag-printing function of the formatter is called with t as argument.
973 val pp_set_tags : formatter -> bool -> unit
977 val set_tags : bool -> unit
982 pp_set_tags ppf b turns on or off the treatment of semantic tags
985 (default is off).
986 val pp_set_print_tags : formatter -> bool -> unit
990 val set_print_tags : bool -> unit
995 pp_set_print_tags ppf b turns on or off the tag-printing operations.
998 val pp_set_mark_tags : formatter -> bool -> unit
1002 val set_mark_tags : bool -> unit
1007 pp_set_mark_tags ppf b turns on or off the tag-marking operations.
1010 val pp_get_print_tags : formatter -> unit -> bool
1014 val get_print_tags : unit -> bool
1019 Return the current status of tag-printing operations.
1021 val pp_get_mark_tags : formatter -> unit -> bool
1025 val get_mark_tags : unit -> bool
1030 Return the current status of tag-marking operations.
1032 val pp_set_formatter_out_channel : formatter -> out_channel -> unit
1036 Redirecting the standard formatter output
1039 val set_formatter_out_channel : out_channel -> unit
1040 Redirect the standard pretty-printer output to the given channel. (All
1042 the output functions of the standard formatter are set to the default
1043 output functions printing to the given channel.)
1044 set_formatter_out_channel is equivalent to Format.pp_set_format‐
1047 ter_out_channel std_formatter .
1048 val pp_set_formatter_output_functions : formatter -> (string -> int ->
1052 int -> unit) -> (unit -> unit) -> unit
1053 val set_formatter_output_functions : (string -> int -> int -> unit) ->
1058 (unit -> unit) -> unit
1059 pp_set_formatter_output_functions ppf out flush redirects the standard
1062 pretty-printer output functions to the functions out and flush .
1063 The out function performs all the pretty-printer string output. It is
1065 called with a string s , a start position p , and a number of charac‐
1066 ters n ; it is supposed to output characters p to p + n - 1 of s .
1067 The flush function is called whenever the pretty-printer is flushed
1069 (via conversion %! , or pretty-printing indications @? or @. , or
1070 using low level functions print_flush or print_newline ).
1071 val pp_get_formatter_output_functions : formatter -> unit -> (string ->
1075 int -> int -> unit) * (unit -> unit)
1076 val get_formatter_output_functions : unit -> (string -> int -> int ->
1081 unit) * (unit -> unit)
1082 Return the current output functions of the standard pretty-printer.
1084 Redefining formatter output
1089 The Format module is versatile enough to let you completely redefine
1090 the meaning of pretty-printing output: you may provide your own func‐
1091 tions to define how to handle indentation, line splitting, and even
1092 printing of all the characters that have to be printed!
1093 Redefining output functions
1095 type formatter_out_functions = {
1096 out_string : string -> int -> int -> unit ;
1097 out_flush : unit -> unit ;
1098 out_newline : unit -> unit ;
1099 out_spaces : int -> unit ;
1100 out_indent : int -> unit ;
1101 }
1102 The set of output functions specific to a formatter:
1105 -the out_string function performs all the pretty-printer string output.
1107 It is called with a string s , a start position p , and a number of
1108 characters n ; it is supposed to output characters p to p + n - 1 of s
1109 .
1110 -the out_flush function flushes the pretty-printer output device.
1112 - out_newline is called to open a new line when the pretty-printer
1114 splits the line.
1115 -the out_spaces function outputs spaces when a break hint leads to spa‐
1117 ces instead of a line split. It is called with the number of spaces to
1118 output.
1119 -the out_indent function performs new line indentation when the
1121 pretty-printer splits the line. It is called with the indentation value
1122 of the new line.
1123 By default:
1125 -fields out_string and out_flush are output device specific; (e.g.
1127 output_string and flush for a out_channel device, or Buffer.add_sub‐
1128 string and ignore for a Buffer.t output device),
1129 -field out_newline is equivalent to out_string \n 0 1 ;
1131 -fields out_spaces and out_indent are equivalent to out_string
1133 (String.make n ' ') 0 n .
1134 Since 4.01.0
1138 val pp_set_formatter_out_functions : formatter -> formatter_out_func‐
1142 tions -> unit
1143 val set_formatter_out_functions : formatter_out_functions -> unit
1148 pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer
1151 output functions of ppf to those of argument out_funs ,
1152 This way, you can change the meaning of indentation (which can be some‐
1154 thing else than just printing space characters) and the meaning of new
1155 lines opening (which can be connected to any other action needed by the
1156 application at hand).
1157 Reasonable defaults for functions out_spaces and out_newline are
1159 respectively out_funs.out_string (String.make n ' ') 0 n and
1160 out_funs.out_string \n 0 1 .
1161 Since 4.01.0
1164 val pp_get_formatter_out_functions : formatter -> unit -> format‐
1168 ter_out_functions
1169 val get_formatter_out_functions : unit -> formatter_out_functions
1174 Return the current output functions of the pretty-printer, including
1176 line splitting and indentation functions. Useful to record the current
1177 setting and restore it afterwards.
1178 Since 4.01.0
1181 Redefining semantic tag operations
1186 type formatter_stag_functions = {
1187 mark_open_stag : stag -> string ;
1188 mark_close_stag : stag -> string ;
1189 print_open_stag : stag -> unit ;
1190 print_close_stag : stag -> unit ;
1191 }
1192 The semantic tag handling functions specific to a formatter: mark ver‐
1195 sions are the 'tag-marking' functions that associate a string marker to
1196 a tag in order for the pretty-printing engine to write those markers as
1197 0 length tokens in the output device of the formatter. print versions
1198 are the 'tag-printing' functions that can perform regular printing when
1199 a tag is closed or opened.
1200 val pp_set_formatter_stag_functions : formatter -> formatter_stag_func‐
1204 tions -> unit
1205 val set_formatter_stag_functions : formatter_stag_functions -> unit
1210 pp_set_formatter_stag_functions ppf tag_funs changes the meaning of
1213 opening and closing semantic tag operations to use the functions in
1214 tag_funs when printing on ppf .
1215 When opening a semantic tag with name t , the string t is passed to the
1217 opening tag-marking function (the mark_open_stag field of the record
1218 tag_funs ), that must return the opening tag marker for that name. When
1219 the next call to close_stag () happens, the semantic tag name t is sent
1220 back to the closing tag-marking function (the mark_close_stag field of
1221 record tag_funs ), that must return a closing tag marker for that name.
1222 The print_ field of the record contains the tag-printing functions that
1224 are called at tag opening and tag closing time, to output regular mate‐
1225 rial in the pretty-printer queue.
1226 val pp_get_formatter_stag_functions : formatter -> unit -> format‐
1230 ter_stag_functions
1231 val get_formatter_stag_functions : unit -> formatter_stag_functions
1236 Return the current semantic tag operation functions of the standard
1238 pretty-printer.
1239 Defining formatters
1244 Defining new formatters permits unrelated output of material in paral‐
1245 lel on several output devices. All the parameters of a formatter are
1246 local to the formatter: right margin, maximum indentation limit, maxi‐
1247 mum number of pretty-printing boxes simultaneously open, ellipsis, and
1248 so on, are specific to each formatter and may be fixed independently.
1249 For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b
1251 returns a new formatter using buffer b as its output device. Simi‐
1252 larly, given a out_channel output channel oc , Format.format‐
1253 ter_of_out_channel oc returns a new formatter using channel oc as its
1254 output device.
1255 Alternatively, given out_funs , a complete set of output functions for
1257 a formatter, then Format.formatter_of_out_functions out_funs computes a
1258 new formatter using those functions for output.
1259 val formatter_of_out_channel : out_channel -> formatter
1261 formatter_of_out_channel oc returns a new formatter writing to the cor‐
1264 responding output channel oc .
1265 val std_formatter : formatter
1269 The standard formatter to write to standard output.
1271 It is defined as Format.formatter_of_out_channel stdout .
1273 val err_formatter : formatter
1277 A formatter to write to standard error.
1279 It is defined as Format.formatter_of_out_channel stderr .
1281 val formatter_of_buffer : Buffer.t -> formatter
1285 formatter_of_buffer b returns a new formatter writing to buffer b . At
1288 the end of pretty-printing, the formatter must be flushed using For‐
1289 mat.pp_print_flush or Format.pp_print_newline , to print all the pend‐
1290 ing material into the buffer.
1291 val stdbuf : Buffer.t
1295 The string buffer in which str_formatter writes.
1297 val str_formatter : formatter
1301 A formatter to output to the Format.stdbuf string buffer.
1303 str_formatter is defined as Format.formatter_of_buffer Format.stdbuf .
1306 val flush_str_formatter : unit -> string
1310 Returns the material printed with str_formatter , flushes the formatter
1312 and resets the corresponding buffer.
1313 val make_formatter : (string -> int -> int -> unit) -> (unit -> unit)
1317 -> formatter
1318 make_formatter out flush returns a new formatter that outputs with
1321 function out , and flushes with function flush .
1322 For instance, make_formatter (Stdlib.output oc) (fun () -> Stdlib.flush
1324 oc) returns a formatter to the out_channel oc .
1325 val formatter_of_out_functions : formatter_out_functions -> formatter
1329 formatter_of_out_functions out_funs returns a new formatter that writes
1332 with the set of output functions out_funs .
1333 See definition of type Format.formatter_out_functions for the meaning
1335 of argument out_funs .
1336 Since 4.06.0
1339 Symbolic pretty-printing
1344 Symbolic pretty-printing is pretty-printing using a symbolic formatter,
1345 i.e. a formatter that outputs symbolic pretty-printing items.
1346 When using a symbolic formatter, all regular pretty-printing activities
1348 occur but output material is symbolic and stored in a buffer of output
1349 items. At the end of pretty-printing, flushing the output buffer
1350 allows post-processing of symbolic output before performing low level
1351 output operations.
1352 In practice, first define a symbolic output buffer b using:
1354 - let sob = make_symbolic_output_buffer () . Then define a symbolic
1356 formatter with:
1357 - let ppf = formatter_of_symbolic_output_buffer sob
1359 Use symbolic formatter ppf as usual, and retrieve symbolic items at end
1361 of pretty-printing by flushing symbolic output buffer sob with:
1362 - flush_symbolic_output_buffer sob .
1364 type symbolic_output_item =
1367 | Output_flush (* symbolic flush command
1368 *)
1369 | Output_newline (* symbolic newline command
1370 *)
1371 | Output_string of string
1372 (* Output_string s : symbolic output for string s
1373 *)
1375 | Output_spaces of int
1376 (* Output_spaces n : symbolic command to output n spaces
1377 *)
1378 | Output_indent of int
1379 (* Output_indent i : symbolic indentation of size i
1380 *)
1382 Items produced by symbolic pretty-printers
1385 Since 4.06.0
1388 type symbolic_output_buffer
1391 The output buffer of a symbolic pretty-printer.
1394 Since 4.06.0
1397 val make_symbolic_output_buffer : unit -> symbolic_output_buffer
1401 make_symbolic_output_buffer () returns a fresh buffer for symbolic out‐
1404 put.
1405 Since 4.06.0
1408 val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
1412 clear_symbolic_output_buffer sob resets buffer sob .
1415 Since 4.06.0
1418 val get_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1422 bolic_output_item list
1423 get_symbolic_output_buffer sob returns the contents of buffer sob .
1426 Since 4.06.0
1429 val flush_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1433 bolic_output_item list
1434 flush_symbolic_output_buffer sob returns the contents of buffer sob and
1437 resets buffer sob . flush_symbolic_output_buffer sob is equivalent to
1438 let items = get_symbolic_output_buffer sob in clear_symbolic_out‐
1439 put_buffer sob; items
1440 Since 4.06.0
1444 val add_symbolic_output_item : symbolic_output_buffer -> symbolic_out‐
1448 put_item -> unit
1449 add_symbolic_output_item sob itm adds item itm to buffer sob .
1452 Since 4.06.0
1455 val formatter_of_symbolic_output_buffer : symbolic_output_buffer ->
1459 formatter
1460 formatter_of_symbolic_output_buffer sob returns a symbolic formatter
1463 that outputs to symbolic_output_buffer sob .
1464 Since 4.06.0
1467 Convenience formatting functions.
1472 val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter
1473 -> 'a -> unit) -> formatter -> 'a list -> unit
1474 pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to
1477 print each item, and calling pp_sep between items ( pp_sep defaults to
1478 Format.pp_print_cut . Does nothing on empty lists.
1479 Since 4.02.0
1482 val pp_print_text : formatter -> string -> unit
1486 pp_print_text ppf s prints s with spaces and newlines respectively
1489 printed using Format.pp_print_space and Format.pp_force_newline .
1490 Since 4.02.0
1493 val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter
1497 -> 'a -> unit) -> formatter -> 'a option -> unit
1498 pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is
1501 Some v and none if it is None . none prints nothing by default.
1502 Since 4.08
1505 val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter
1509 -> 'e -> unit) -> formatter -> ('a, 'e) result -> unit
1510 pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _
1513 and error if r is Error _ .
1514 Since 4.08
1517 Formatted pretty-printing
1522 Module Format provides a complete set of printf like functions for
1523 pretty-printing using format string specifications.
1524 Specific annotations may be added in the format strings to give
1526 pretty-printing commands to the pretty-printing engine.
1527 Those annotations are introduced in the format strings using the @
1529 character. For instance, @ means a space break, @, means a cut, @[
1530 opens a new box, and @] closes the last open box.
1531 val fprintf : formatter -> ('a, formatter, unit) format -> 'a
1533 fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN accord‐
1539 ing to the format string fmt , and outputs the resulting string on the
1540 formatter ff .
1541 The format string fmt is a character string which contains three types
1543 of objects: plain characters and conversion specifications as specified
1544 in the Printf module, and pretty-printing indications specific to the
1545 Format module.
1546 The pretty-printing indication characters are introduced by a @ charac‐
1548 ter, and their meanings are:
1549 - @[ : open a pretty-printing box. The type and offset of the box may
1551 be optionally specified with the following syntax: the < character,
1552 followed by an optional box type indication, then an optional integer
1553 offset, and the closing > character. Pretty-printing box type is one
1554 of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
1555 pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box,
1556 ' hv ' stands for an 'horizontal/vertical' pretty-printing box, ' b '
1557 stands for an 'horizontal-or-vertical' pretty-printing box demonstrat‐
1558 ing indentation, ' hov ' stands a simple 'horizontal-or-vertical'
1559 pretty-printing box. For instance, @[<hov 2> opens an 'horizon‐
1560 tal-or-vertical' pretty-printing box with indentation 2 as obtained
1561 with open_hovbox 2 . For more details about pretty-printing boxes, see
1562 the various box opening functions open_*box .
1563 - @] : close the most recently opened pretty-printing box.
1565 - @, : output a 'cut' break hint, as with print_cut () .
1567 - @ : output a 'space' break hint, as with print_space () .
1569 - @; : output a 'full' break hint as with print_break . The nspaces and
1571 offset parameters of the break hint may be optionally specified with
1572 the following syntax: the < character, followed by an integer nspaces
1573 value, then an integer offset , and a closing > character. If no
1574 parameters are provided, the good break defaults to a 'space' break
1575 hint.
1576 - @. : flush the pretty-printer and split the line, as with print_new‐
1578 line () .
1579 - @<n> : print the following item as if it were of length n . Hence,
1581 printf @<0>%s arg prints arg as a zero length string. If @<n> is not
1582 followed by a conversion specification, then the following character of
1583 the format is printed as if it were of length n .
1584 - @{ : open a semantic tag. The name of the tag may be optionally spec‐
1586 ified with the following syntax: the < character, followed by an
1587 optional string specification, and the closing > character. The string
1588 specification is any character string that does not contain the closing
1589 character '>' . If omitted, the tag name defaults to the empty string.
1590 For more details about semantic tags, see the functions For‐
1591 mat.open_stag and Format.close_stag .
1592 - @} : close the most recently opened semantic tag.
1594 - @? : flush the pretty-printer as with print_flush () . This is
1596 equivalent to the conversion %! .
1597 - @\n : force a newline, as with force_newline () , not the normal way
1599 of pretty-printing, you should prefer using break hints inside a verti‐
1600 cal pretty-printing box.
1601 Note: To prevent the interpretation of a @ character as a pretty-print‐
1603 ing indication, escape it with a % character. Old quotation mode @@ is
1604 deprecated since it is not compatible with formatted input interpreta‐
1605 tion of character '@' .
1606 Example: printf @[%s@ %d@]@. x = 1 is equivalent to open_box ();
1608 print_string x = ; print_space (); print_int 1; close_box ();
1609 print_newline () . It prints x = 1 within a pretty-printing 'horizon‐
1610 tal-or-vertical' box.
1611 val printf : ('a, formatter, unit) format -> 'a
1613 Same as fprintf above, but output on std_formatter .
1615 val eprintf : ('a, formatter, unit) format -> 'a
1619 Same as fprintf above, but output on err_formatter .
1621 val sprintf : ('a, unit, string) format -> 'a
1625 Same as printf above, but instead of printing on a formatter, returns a
1627 string containing the result of formatting the arguments. Note that
1628 the pretty-printer queue is flushed at the end of each call to sprintf
1629 .
1630 In case of multiple and related calls to sprintf to output material on
1632 a single string, you should consider using fprintf with the predefined
1633 formatter str_formatter and call flush_str_formatter () to get the
1634 final result.
1635 Alternatively, you can use Format.fprintf with a formatter writing to a
1637 buffer of your own: flushing the formatter and the buffer at the end of
1638 pretty-printing returns the desired string.
1639 val asprintf : ('a, formatter, unit, string) format4 -> 'a
1643 Same as printf above, but instead of printing on a formatter, returns a
1645 string containing the result of formatting the arguments. The type of
1646 asprintf is general enough to interact nicely with %a conversions.
1647 Since 4.01.0
1650 val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
1654 Same as Format.fprintf , except the formatter is the last argument.
1656 dprintf ... a b c is a function of type formatter -> unit which can be
1657 given to a format specifier %t .
1658 This can be used as a replacement for Format.asprintf to delay format‐
1660 ting decisions. Using the string returned by Format.asprintf in a for‐
1661 matting context forces formatting decisions to be taken in isolation,
1662 and the final string may be created prematurely. Format.dprintf allows
1663 delay of formatting decisions until the final formatting context is
1664 known. For example: let t = Format.dprintf %i@ %i@ %i 1 2 3 in ...
1665 Format.printf @[<v>%t@] t
1666 Since 4.08.0
1670 val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
1674 Same as fprintf above, but does not print anything. Useful to ignore
1676 some material when conditionally printing.
1677 Since 3.10.0
1680 Formatted Pretty-Printing with continuations.
1685 val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1687 'a) format4 -> 'b
1688 Same as fprintf above, but instead of returning immediately, passes the
1690 formatter to its first argument at the end of printing.
1691 val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a)
1695 format4 -> 'b
1696 Same as Format.dprintf above, but instead of returning immediately,
1698 passes the suspended printer to its first argument at the end of print‐
1699 ing.
1700 Since 4.08.0
1703 val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1707 'a) format4 -> 'b
1708 Same as kfprintf above, but does not print anything. Useful to ignore
1710 some material when conditionally printing.
1711 Since 3.12.0
1714 val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1718 Same as sprintf above, but instead of returning the string, passes it
1720 to the first argument.
1721 val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 ->
1725 'b
1726 Same as asprintf above, but instead of returning the string, passes it
1728 to the first argument.
1729 Since 4.03
1732 Deprecated
1737 val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
1738 Deprecated. This function is error prone. Do not use it. This func‐
1740 tion is neither compositional nor incremental, since it flushes the
1741 pretty-printer queue at each call.
1742 If you need to print to some buffer b , you must first define a format‐
1744 ter writing to b , using let to_b = formatter_of_buffer b ; then use
1745 regular calls to Format.fprintf with formatter to_b .
1746 val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1750 Deprecated. An alias for ksprintf .
1752 val set_all_formatter_output_functions : out:(string -> int -> int ->
1756 unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int
1757 -> unit) -> unit
1758 Deprecated. Subsumed by set_formatter_out_functions .
1760 val get_all_formatter_output_functions : unit -> (string -> int -> int
1764 -> unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
1765 Deprecated. Subsumed by get_formatter_out_functions .
1767 val pp_set_all_formatter_output_functions : formatter -> out:(string ->
1771 int -> int -> unit) -> flush:(unit -> unit) -> newline:(unit -> unit)
1772 -> spaces:(int -> unit) -> unit
1773 Deprecated. Subsumed by pp_set_formatter_out_functions .
1775 val pp_get_all_formatter_output_functions : formatter -> unit ->
1779 (string -> int -> int -> unit) * (unit -> unit) * (unit -> unit) * (int
1780 -> unit)
1781 Deprecated. Subsumed by pp_get_formatter_out_functions .
1783 String tags
1788 val pp_open_tag : formatter -> tag -> unit
1789 Deprecated. Subsumed by Format.pp_open_stag .
1791 val open_tag : tag -> unit
1795 Deprecated. Subsumed by Format.open_stag .
1797 val pp_close_tag : formatter -> unit -> unit
1801 Deprecated. Subsumed by Format.pp_close_stag .
1803 val close_tag : unit -> unit
1807 Deprecated. Subsumed by Format.close_stag .
1809 type formatter_tag_functions = {
1812 mark_open_tag : tag -> string ;
1813 mark_close_tag : tag -> string ;
1814 print_open_tag : tag -> unit ;
1815 print_close_tag : tag -> unit ;
1816 }
1817 Deprecated. Subsumed by Format.formatter_stag_functions .
1820 val pp_set_formatter_tag_functions : formatter -> formatter_tag_func‐
1824 tions -> unit
1825 Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
1827 This function will erase non-string tag formatting functions.
1830 val set_formatter_tag_functions : formatter_tag_functions -> unit
1834 Deprecated. Subsumed by Format.set_formatter_stag_functions .
1836 val pp_get_formatter_tag_functions : formatter -> unit -> format‐
1840 ter_tag_functions
1841 Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
1843 val get_formatter_tag_functions : unit -> formatter_tag_functions
1847 Deprecated. Subsumed by Format.get_formatter_stag_functions .
1849OCamldoc 2019-07-30 Format(3)