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 ();
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
418 (according 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.
463 Using 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
510 efficiency.
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.
590 Either decreasing the length of the parent box to make it fit on a
591 line:
592 printf "@[123456@[7@]89@]@."
593 or opening an intermediary box before the maximum indentation limit
594 which fits on the current line
595 printf "@[123@[456@[7@]89@]A@]@."
596 avoids the rejection to the left of the inner boxes and print respec‐
597 tively "123456789" and "123456789A" . Note also that vertical boxes
598 never fit on a line whereas horizontal boxes always fully fit on the
599 current line. Opening a box may split a line whereas the contents may
600 have fit. If this behavior is problematic, it can be curtailed by set‐
601 ting the maximum indentation limit to margin - 1 . Note that setting
602 the maximum indentation limit to margin is invalid.
603 Nothing happens if d is smaller than 2.
605 If d is too large, the limit is set to the maximum admissible value
607 (which is greater than 10 ^ 9 ).
608 If d is greater or equal than the current margin, it is ignored, and
610 the current maximum indentation limit is kept.
611 See also Format.pp_set_geometry .
613 val pp_get_max_indent : formatter -> unit -> int
617 val get_max_indent : unit -> int
622 Return the maximum indentation limit (in characters).
624 Geometry
629 Geometric functions can be used to manipulate simultaneously the cou‐
630 pled variables, margin and maxixum indentation limit.
631 type geometry = {
633 max_indent : int ;
634 margin : int ;
635 }
636 val check_geometry : geometry -> bool
642 Check if the formatter geometry is valid: 1 < max_indent < margin
644 val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
649 val set_geometry : max_indent:int -> margin:int -> unit
654 val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int ->
659 unit
660 val safe_set_geometry : max_indent:int -> margin:int -> unit
665 pp_set_geometry ppf ~max_indent ~margin sets both the margin and maxi‐
668 mum indentation limit for ppf .
669 When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin
671 is equivalent to pp_set_margin ppf margin; pp_set_max_indent ppf
672 max_indent ; and avoids the subtly incorrect pp_set_max_indent ppf
673 max_indent; pp_set_margin ppf margin ;
674 Outside of this domain, pp_set_geometry raises an invalid argument
676 exception whereas pp_safe_set_geometry does nothing.
677 Since 4.08.0
680 val pp_update_geometry : formatter -> (geometry -> geometry) -> unit
684 pp_update_geometry ppf (fun geo -> { geo with ... }) lets you update a
687 formatter's geometry in a way that is robust to extension of the geome‐
688 try record with new fields.
689 Raises an invalid argument exception if the returned geometry does not
691 satisfy Format.check_geometry .
692 Since 4.11.0
695 val update_geometry : (geometry -> geometry) -> unit
699 val pp_get_geometry : formatter -> unit -> geometry
704 val get_geometry : unit -> geometry
709 Return the current geometry of the formatter
711 Since 4.08.0
714 Maximum formatting depth
719 The maximum formatting depth is the maximum number of pretty-printing
720 boxes simultaneously open.
721 Material inside boxes nested deeper is printed as an ellipsis (more
723 precisely as the text returned by Format.get_ellipsis_text () ).
724 val pp_set_max_boxes : formatter -> int -> unit
726 val set_max_boxes : int -> unit
731 pp_set_max_boxes ppf max sets the maximum number of pretty-printing
734 boxes simultaneously open.
735 Material inside boxes nested deeper is printed as an ellipsis (more
737 precisely as the text returned by Format.get_ellipsis_text () ).
738 Nothing happens if max is smaller than 2.
740 val pp_get_max_boxes : formatter -> unit -> int
744 val get_max_boxes : unit -> int
749 Returns the maximum number of pretty-printing boxes allowed before
751 ellipsis.
752 val pp_over_max_boxes : formatter -> unit -> bool
756 val over_max_boxes : unit -> bool
761 Tests if the maximum number of pretty-printing boxes allowed have
763 already been opened.
764 Tabulation boxes
769 A tabulation box prints material on lines divided into cells of fixed
770 length. A tabulation box provides a simple way to display vertical col‐
771 umns of left adjusted text.
772 This box features command set_tab to define cell boundaries, and com‐
774 mand print_tab to move from cell to cell and split the line when there
775 is no more cells to print on the line.
776 Note: printing within tabulation box is line directed, so arbitrary
778 line splitting inside a tabulation box leads to poor rendering. Yet,
779 controlled use of tabulation boxes allows simple printing of columns
780 within module Format .
781 val pp_open_tbox : formatter -> unit -> unit
783 val open_tbox : unit -> unit
788 open_tbox () opens a new tabulation box.
791 This box prints lines separated into cells of fixed width.
793 Inside a tabulation box, special tabulation markers defines points of
795 interest on the line (for instance to delimit cell boundaries). Func‐
796 tion Format.set_tab sets a tabulation marker at insertion point.
797 A tabulation box features specific tabulation breaks to move to next
799 tabulation marker or split the line. Function Format.print_tbreak
800 prints a tabulation break.
801 val pp_close_tbox : formatter -> unit -> unit
805 val close_tbox : unit -> unit
810 Closes the most recently opened tabulation box.
812 val pp_set_tab : formatter -> unit -> unit
816 val set_tab : unit -> unit
821 Sets a tabulation marker at current insertion point.
823 val pp_print_tab : formatter -> unit -> unit
827 val print_tab : unit -> unit
832 print_tab () emits a 'next' tabulation break hint: if not already set
835 on a tabulation marker, the insertion point moves to the first tabula‐
836 tion marker on the right, or the pretty-printer splits the line and
837 insertion point moves to the leftmost tabulation marker.
838 It is equivalent to print_tbreak 0 0 .
840 val pp_print_tbreak : formatter -> int -> int -> unit
844 val print_tbreak : int -> int -> unit
849 print_tbreak nspaces offset emits a 'full' tabulation break hint.
852 If not already set on a tabulation marker, the insertion point moves to
854 the first tabulation marker on the right and the pretty-printer prints
855 nspaces spaces.
856 If there is no next tabulation marker on the right, the pretty-printer
858 splits the line at this point, then insertion point moves to the left‐
859 most tabulation marker of the box.
860 If the pretty-printer splits the line, offset is added to the current
862 indentation.
863 Ellipsis
868 val pp_set_ellipsis_text : formatter -> string -> unit
869 val set_ellipsis_text : string -> unit
874 Set the text of the ellipsis printed when too many pretty-printing
876 boxes are open (a single dot, . , by default).
877 val pp_get_ellipsis_text : formatter -> unit -> string
881 val get_ellipsis_text : unit -> string
886 Return the text of the ellipsis.
888 Semantic tags
893 type stag = ..
894 Semantic tags (or simply tags) are user's defined annotations to asso‐
897 ciate user's specific operations to printed entities.
898 Common usage of semantic tags is text decoration to get specific font
900 or text size rendering for a display device, or marking delimitation of
901 entities (e.g. HTML or TeX elements or terminal escape sequences).
902 More sophisticated usage of semantic tags could handle dynamic modifi‐
903 cation of the pretty-printer behavior to properly print the material
904 within some specific tags. For instance, we can define an RGB tag like
905 so:
906 type stag += RGB of {r:int;g:int;b:int}
907 In order to properly delimit printed entities, a semantic tag must be
910 opened before and closed after the entity. Semantic tags must be prop‐
911 erly nested like parentheses using Format.pp_open_stag and For‐
912 mat.pp_close_stag .
913 Tag specific operations occur any time a tag is opened or closed, At
915 each occurrence, two kinds of operations are performed tag-marking and
916 tag-printing:
917 -The tag-marking operation is the simpler tag specific operation: it
919 simply writes a tag specific string into the output device of the for‐
920 matter. Tag-marking does not interfere with line-splitting computation.
921 -The tag-printing operation is the more involved tag specific opera‐
923 tion: it can print arbitrary material to the formatter. Tag-printing is
924 tightly linked to the current pretty-printer operations.
925 Roughly speaking, tag-marking is commonly used to get a better render‐
927 ing of texts in the rendering device, while tag-printing allows fine
928 tuning of printing routines to print the same entity differently
929 according to the semantic tags (i.e. print additional material or even
930 omit parts of the output).
931 More precisely: when a semantic tag is opened or closed then both and
933 successive 'tag-printing' and 'tag-marking' operations occur:
934 -Tag-printing a semantic tag means calling the formatter specific func‐
936 tion print_open_stag (resp. print_close_stag ) with the name of the
937 tag as argument: that tag-printing function can then print any regular
938 material to the formatter (so that this material is enqueued as usual
939 in the formatter queue for further line splitting computation).
940 -Tag-marking a semantic tag means calling the formatter specific func‐
942 tion mark_open_stag (resp. mark_close_stag ) with the name of the tag
943 as argument: that tag-marking function can then return the 'tag-opening
944 marker' (resp. `tag-closing marker') for direct output into the output
945 device of the formatter.
946 Being written directly into the output device of the formatter, seman‐
948 tic tag marker strings are not considered as part of the printing mate‐
949 rial that drives line splitting (in other words, the length of the
950 strings corresponding to tag markers is considered as zero for line
951 splitting).
952 Thus, semantic tag handling is in some sense transparent to
954 pretty-printing and does not interfere with usual indentation. Hence, a
955 single pretty-printing routine can output both simple 'verbatim' mate‐
956 rial or richer decorated output depending on the treatment of tags. By
957 default, tags are not active, hence the output is not decorated with
958 tag information. Once set_tags is set to true , the pretty-printer
959 engine honors tags and decorates the output accordingly.
960 Default tag-marking functions behave the HTML way: Format.tag are
962 enclosed in "<" and ">" while other tags are ignored; hence, opening
963 marker for tag string "t" is "<t>" and closing marker is "</t>" .
964 Default tag-printing functions just do nothing.
966 Tag-marking and tag-printing functions are user definable and can be
968 set by calling Format.set_formatter_stag_functions .
969 Semantic tag operations may be set on or off with Format.set_tags .
971 Tag-marking operations may be set on or off with Format.set_mark_tags .
972 Tag-printing operations may be set on or off with Format.set_print_tags
973 .
974 type tag = string
977 type stag +=
982 | String_tag of tag (* String_tag s is a string tag s . String tags
983 can be inserted either by explicitly using the constructor String_tag
984 or by using the dedicated format syntax "@{<s> ... @}" .
985 *)
986 val pp_open_stag : formatter -> stag -> unit
992 val open_stag : stag -> unit
997 pp_open_stag ppf t opens the semantic tag named t .
1000 The print_open_stag tag-printing function of the formatter is called
1002 with t as argument; then the opening tag marker for t , as given by
1003 mark_open_stag t , is written into the output device of the formatter.
1004 val pp_close_stag : formatter -> unit -> unit
1008 val close_stag : unit -> unit
1013 pp_close_stag ppf () closes the most recently opened semantic tag t .
1016 The closing tag marker, as given by mark_close_stag t , is written into
1018 the output device of the formatter; then the print_close_stag
1019 tag-printing function of the formatter is called with t as argument.
1020 val pp_set_tags : formatter -> bool -> unit
1024 val set_tags : bool -> unit
1029 pp_set_tags ppf b turns on or off the treatment of semantic tags
1032 (default is off).
1033 val pp_set_print_tags : formatter -> bool -> unit
1037 val set_print_tags : bool -> unit
1042 pp_set_print_tags ppf b turns on or off the tag-printing operations.
1045 val pp_set_mark_tags : formatter -> bool -> unit
1049 val set_mark_tags : bool -> unit
1054 pp_set_mark_tags ppf b turns on or off the tag-marking operations.
1057 val pp_get_print_tags : formatter -> unit -> bool
1061 val get_print_tags : unit -> bool
1066 Return the current status of tag-printing operations.
1068 val pp_get_mark_tags : formatter -> unit -> bool
1072 val get_mark_tags : unit -> bool
1077 Return the current status of tag-marking operations.
1079 val pp_set_formatter_out_channel : formatter -> out_channel -> unit
1083 Redirecting the standard formatter output
1086 val set_formatter_out_channel : out_channel -> unit
1087 Redirect the standard pretty-printer output to the given channel. (All
1089 the output functions of the standard formatter are set to the default
1090 output functions printing to the given channel.)
1091 set_formatter_out_channel is equivalent to Format.pp_set_format‐
1094 ter_out_channel std_formatter .
1095 val pp_set_formatter_output_functions : formatter -> (string -> int ->
1099 int -> unit) -> (unit -> unit) -> unit
1100 val set_formatter_output_functions : (string -> int -> int -> unit) ->
1105 (unit -> unit) -> unit
1106 pp_set_formatter_output_functions ppf out flush redirects the standard
1109 pretty-printer output functions to the functions out and flush .
1110 The out function performs all the pretty-printer string output. It is
1112 called with a string s , a start position p , and a number of charac‐
1113 ters n ; it is supposed to output characters p to p + n - 1 of s .
1114 The flush function is called whenever the pretty-printer is flushed
1116 (via conversion %! , or pretty-printing indications @? or @. , or
1117 using low level functions print_flush or print_newline ).
1118 val pp_get_formatter_output_functions : formatter -> unit -> (string ->
1122 int -> int -> unit) * (unit -> unit)
1123 val get_formatter_output_functions : unit -> (string -> int -> int ->
1128 unit) * (unit -> unit)
1129 Return the current output functions of the standard pretty-printer.
1131 Redefining formatter output
1136 The Format module is versatile enough to let you completely redefine
1137 the meaning of pretty-printing output: you may provide your own func‐
1138 tions to define how to handle indentation, line splitting, and even
1139 printing of all the characters that have to be printed!
1140 Redefining output functions
1142 type formatter_out_functions = {
1143 out_string : string -> int -> int -> unit ;
1144 out_flush : unit -> unit ;
1145 out_newline : unit -> unit ;
1146 out_spaces : int -> unit ;
1147 out_indent : int -> unit ;
1148 }
1149 The set of output functions specific to a formatter:
1152 -the out_string function performs all the pretty-printer string output.
1154 It is called with a string s , a start position p , and a number of
1155 characters n ; it is supposed to output characters p to p + n - 1 of s
1156 .
1157 -the out_flush function flushes the pretty-printer output device.
1159 - out_newline is called to open a new line when the pretty-printer
1161 splits the line.
1162 -the out_spaces function outputs spaces when a break hint leads to spa‐
1164 ces instead of a line split. It is called with the number of spaces to
1165 output.
1166 -the out_indent function performs new line indentation when the
1168 pretty-printer splits the line. It is called with the indentation value
1169 of the new line.
1170 By default:
1172 -fields out_string and out_flush are output device specific; (e.g.
1174 output_string and flush for a out_channel device, or Buffer.add_sub‐
1175 string and ignore for a Buffer.t output device),
1176 -field out_newline is equivalent to out_string "\n" 0 1 ;
1178 -fields out_spaces and out_indent are equivalent to out_string
1180 (String.make n ' ') 0 n .
1181 Since 4.01.0
1185 val pp_set_formatter_out_functions : formatter -> formatter_out_func‐
1189 tions -> unit
1190 val set_formatter_out_functions : formatter_out_functions -> unit
1195 pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer
1198 output functions of ppf to those of argument out_funs ,
1199 This way, you can change the meaning of indentation (which can be some‐
1201 thing else than just printing space characters) and the meaning of new
1202 lines opening (which can be connected to any other action needed by the
1203 application at hand).
1204 Reasonable defaults for functions out_spaces and out_newline are
1206 respectively out_funs.out_string (String.make n ' ') 0 n and
1207 out_funs.out_string "\n" 0 1 .
1208 Since 4.01.0
1211 val pp_get_formatter_out_functions : formatter -> unit -> format‐
1215 ter_out_functions
1216 val get_formatter_out_functions : unit -> formatter_out_functions
1221 Return the current output functions of the pretty-printer, including
1223 line splitting and indentation functions. Useful to record the current
1224 setting and restore it afterwards.
1225 Since 4.01.0
1228 Redefining semantic tag operations
1233 type formatter_stag_functions = {
1234 mark_open_stag : stag -> string ;
1235 mark_close_stag : stag -> string ;
1236 print_open_stag : stag -> unit ;
1237 print_close_stag : stag -> unit ;
1238 }
1239 The semantic tag handling functions specific to a formatter: mark ver‐
1242 sions are the 'tag-marking' functions that associate a string marker to
1243 a tag in order for the pretty-printing engine to write those markers as
1244 0 length tokens in the output device of the formatter. print versions
1245 are the 'tag-printing' functions that can perform regular printing when
1246 a tag is closed or opened.
1247 val pp_set_formatter_stag_functions : formatter -> formatter_stag_func‐
1251 tions -> unit
1252 val set_formatter_stag_functions : formatter_stag_functions -> unit
1257 pp_set_formatter_stag_functions ppf tag_funs changes the meaning of
1260 opening and closing semantic tag operations to use the functions in
1261 tag_funs when printing on ppf .
1262 When opening a semantic tag with name t , the string t is passed to the
1264 opening tag-marking function (the mark_open_stag field of the record
1265 tag_funs ), that must return the opening tag marker for that name. When
1266 the next call to close_stag () happens, the semantic tag name t is sent
1267 back to the closing tag-marking function (the mark_close_stag field of
1268 record tag_funs ), that must return a closing tag marker for that name.
1269 The print_ field of the record contains the tag-printing functions that
1271 are called at tag opening and tag closing time, to output regular mate‐
1272 rial in the pretty-printer queue.
1273 val pp_get_formatter_stag_functions : formatter -> unit -> format‐
1277 ter_stag_functions
1278 val get_formatter_stag_functions : unit -> formatter_stag_functions
1283 Return the current semantic tag operation functions of the standard
1285 pretty-printer.
1286 Defining formatters
1291 Defining new formatters permits unrelated output of material in paral‐
1292 lel on several output devices. All the parameters of a formatter are
1293 local to the formatter: right margin, maximum indentation limit, maxi‐
1294 mum number of pretty-printing boxes simultaneously open, ellipsis, and
1295 so on, are specific to each formatter and may be fixed independently.
1296 For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b
1298 returns a new formatter using buffer b as its output device. Simi‐
1299 larly, given a out_channel output channel oc , Format.format‐
1300 ter_of_out_channel oc returns a new formatter using channel oc as its
1301 output device.
1302 Alternatively, given out_funs , a complete set of output functions for
1304 a formatter, then Format.formatter_of_out_functions out_funs computes a
1305 new formatter using those functions for output.
1306 val formatter_of_out_channel : out_channel -> formatter
1308 formatter_of_out_channel oc returns a new formatter writing to the cor‐
1311 responding output channel oc .
1312 val std_formatter : formatter
1316 The standard formatter to write to standard output.
1318 It is defined as Format.formatter_of_out_channel stdout .
1320 val err_formatter : formatter
1324 A formatter to write to standard error.
1326 It is defined as Format.formatter_of_out_channel stderr .
1328 val formatter_of_buffer : Buffer.t -> formatter
1332 formatter_of_buffer b returns a new formatter writing to buffer b . At
1335 the end of pretty-printing, the formatter must be flushed using For‐
1336 mat.pp_print_flush or Format.pp_print_newline , to print all the pend‐
1337 ing material into the buffer.
1338 val stdbuf : Buffer.t
1342 The string buffer in which str_formatter writes.
1344 val str_formatter : formatter
1348 A formatter to output to the Format.stdbuf string buffer.
1350 str_formatter is defined as Format.formatter_of_buffer Format.stdbuf .
1353 val flush_str_formatter : unit -> string
1357 Returns the material printed with str_formatter , flushes the formatter
1359 and resets the corresponding buffer.
1360 val make_formatter : (string -> int -> int -> unit) -> (unit -> unit)
1364 -> formatter
1365 make_formatter out flush returns a new formatter that outputs with
1368 function out , and flushes with function flush .
1369 For instance,
1371 make_formatter
1372 (Stdlib.output oc)
1373 (fun () -> Stdlib.flush oc)
1374 returns a formatter to the out_channel oc .
1375 val formatter_of_out_functions : formatter_out_functions -> formatter
1379 formatter_of_out_functions out_funs returns a new formatter that writes
1382 with the set of output functions out_funs .
1383 See definition of type Format.formatter_out_functions for the meaning
1385 of argument out_funs .
1386 Since 4.06.0
1389 Symbolic pretty-printing
1394 Symbolic pretty-printing is pretty-printing using a symbolic formatter,
1395 i.e. a formatter that outputs symbolic pretty-printing items.
1396 When using a symbolic formatter, all regular pretty-printing activities
1398 occur but output material is symbolic and stored in a buffer of output
1399 items. At the end of pretty-printing, flushing the output buffer
1400 allows post-processing of symbolic output before performing low level
1401 output operations.
1402 In practice, first define a symbolic output buffer b using:
1404 - let sob = make_symbolic_output_buffer () . Then define a symbolic
1406 formatter with:
1407 - let ppf = formatter_of_symbolic_output_buffer sob
1409 Use symbolic formatter ppf as usual, and retrieve symbolic items at end
1411 of pretty-printing by flushing symbolic output buffer sob with:
1412 - flush_symbolic_output_buffer sob .
1414 type symbolic_output_item =
1417 | Output_flush (* symbolic flush command
1418 *)
1419 | Output_newline (* symbolic newline command
1420 *)
1421 | Output_string of string
1422 (* Output_string s : symbolic output for string s
1423 *)
1425 | Output_spaces of int
1426 (* Output_spaces n : symbolic command to output n spaces
1427 *)
1428 | Output_indent of int
1429 (* Output_indent i : symbolic indentation of size i
1430 *)
1432 Items produced by symbolic pretty-printers
1435 Since 4.06.0
1438 type symbolic_output_buffer
1441 The output buffer of a symbolic pretty-printer.
1444 Since 4.06.0
1447 val make_symbolic_output_buffer : unit -> symbolic_output_buffer
1451 make_symbolic_output_buffer () returns a fresh buffer for symbolic out‐
1454 put.
1455 Since 4.06.0
1458 val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
1462 clear_symbolic_output_buffer sob resets buffer sob .
1465 Since 4.06.0
1468 val get_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1472 bolic_output_item list
1473 get_symbolic_output_buffer sob returns the contents of buffer sob .
1476 Since 4.06.0
1479 val flush_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1483 bolic_output_item list
1484 flush_symbolic_output_buffer sob returns the contents of buffer sob and
1487 resets buffer sob . flush_symbolic_output_buffer sob is equivalent to
1488 let items = get_symbolic_output_buffer sob in
1489 clear_symbolic_output_buffer sob; items
1490 Since 4.06.0
1494 val add_symbolic_output_item : symbolic_output_buffer -> symbolic_out‐
1498 put_item -> unit
1499 add_symbolic_output_item sob itm adds item itm to buffer sob .
1502 Since 4.06.0
1505 val formatter_of_symbolic_output_buffer : symbolic_output_buffer ->
1509 formatter
1510 formatter_of_symbolic_output_buffer sob returns a symbolic formatter
1513 that outputs to symbolic_output_buffer sob .
1514 Since 4.06.0
1517 Convenience formatting functions.
1522 val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter
1523 -> 'a -> unit) -> formatter -> 'a list -> unit
1524 pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to
1527 print each item, and calling pp_sep between items ( pp_sep defaults to
1528 Format.pp_print_cut . Does nothing on empty lists.
1529 Since 4.02.0
1532 val pp_print_text : formatter -> string -> unit
1536 pp_print_text ppf s prints s with spaces and newlines respectively
1539 printed using Format.pp_print_space and Format.pp_force_newline .
1540 Since 4.02.0
1543 val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter
1547 -> 'a -> unit) -> formatter -> 'a option -> unit
1548 pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is
1551 Some v and none if it is None . none prints nothing by default.
1552 Since 4.08
1555 val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter
1559 -> 'e -> unit) -> formatter -> ('a, 'e) result -> unit
1560 pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _
1563 and error if r is Error _ .
1564 Since 4.08
1567 Formatted pretty-printing
1572 Module Format provides a complete set of printf like functions for
1573 pretty-printing using format string specifications.
1574 Specific annotations may be added in the format strings to give
1576 pretty-printing commands to the pretty-printing engine.
1577 Those annotations are introduced in the format strings using the @
1579 character. For instance, @ means a space break, @, means a cut, @[
1580 opens a new box, and @] closes the last open box.
1581 val fprintf : formatter -> ('a, formatter, unit) format -> 'a
1583 fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN accord‐
1589 ing to the format string fmt , and outputs the resulting string on the
1590 formatter ff .
1591 The format string fmt is a character string which contains three types
1593 of objects: plain characters and conversion specifications as specified
1594 in the Printf module, and pretty-printing indications specific to the
1595 Format module.
1596 The pretty-printing indication characters are introduced by a @ charac‐
1598 ter, and their meanings are:
1599 - @[ : open a pretty-printing box. The type and offset of the box may
1601 be optionally specified with the following syntax: the < character,
1602 followed by an optional box type indication, then an optional integer
1603 offset, and the closing > character. Pretty-printing box type is one
1604 of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
1605 pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box,
1606 ' hv ' stands for an 'horizontal/vertical' pretty-printing box, ' b '
1607 stands for an 'horizontal-or-vertical' pretty-printing box demonstrat‐
1608 ing indentation, ' hov ' stands a simple 'horizontal-or-vertical'
1609 pretty-printing box. For instance, @[<hov 2> opens an 'horizon‐
1610 tal-or-vertical' pretty-printing box with indentation 2 as obtained
1611 with open_hovbox 2 . For more details about pretty-printing boxes, see
1612 the various box opening functions open_*box .
1613 - @] : close the most recently opened pretty-printing box.
1615 - @, : output a 'cut' break hint, as with print_cut () .
1617 - @ : output a 'space' break hint, as with print_space () .
1619 - @; : output a 'full' break hint as with print_break . The nspaces and
1621 offset parameters of the break hint may be optionally specified with
1622 the following syntax: the < character, followed by an integer nspaces
1623 value, then an integer offset , and a closing > character. If no
1624 parameters are provided, the good break defaults to a 'space' break
1625 hint.
1626 - @. : flush the pretty-printer and split the line, as with print_new‐
1628 line () .
1629 - @<n> : print the following item as if it were of length n . Hence,
1631 printf "@<0>%s" arg prints arg as a zero length string. If @<n> is not
1632 followed by a conversion specification, then the following character of
1633 the format is printed as if it were of length n .
1634 - @{ : open a semantic tag. The name of the tag may be optionally spec‐
1636 ified with the following syntax: the < character, followed by an
1637 optional string specification, and the closing > character. The string
1638 specification is any character string that does not contain the closing
1639 character '>' . If omitted, the tag name defaults to the empty string.
1640 For more details about semantic tags, see the functions For‐
1641 mat.open_stag and Format.close_stag .
1642 - @} : close the most recently opened semantic tag.
1644 - @? : flush the pretty-printer as with print_flush () . This is
1646 equivalent to the conversion %! .
1647 - @\n : force a newline, as with force_newline () , not the normal way
1649 of pretty-printing, you should prefer using break hints inside a verti‐
1650 cal pretty-printing box.
1651 Note: To prevent the interpretation of a @ character as a pretty-print‐
1653 ing indication, escape it with a % character. Old quotation mode @@ is
1654 deprecated since it is not compatible with formatted input interpreta‐
1655 tion of character '@' .
1656 Example: printf "@[%s@ %d@]@." "x =" 1 is equivalent to open_box ();
1658 print_string "x ="; print_space ();
1659 print_int 1; close_box (); print_newline () . It prints x = 1
1660 within a pretty-printing 'horizontal-or-vertical' box.
1661 val printf : ('a, formatter, unit) format -> 'a
1663 Same as fprintf above, but output on std_formatter .
1665 val eprintf : ('a, formatter, unit) format -> 'a
1669 Same as fprintf above, but output on err_formatter .
1671 val sprintf : ('a, unit, string) format -> 'a
1675 Same as printf above, but instead of printing on a formatter, returns a
1677 string containing the result of formatting the arguments. Note that
1678 the pretty-printer queue is flushed at the end of each call to sprintf
1679 .
1680 In case of multiple and related calls to sprintf to output material on
1682 a single string, you should consider using fprintf with the predefined
1683 formatter str_formatter and call flush_str_formatter () to get the
1684 final result.
1685 Alternatively, you can use Format.fprintf with a formatter writing to a
1687 buffer of your own: flushing the formatter and the buffer at the end of
1688 pretty-printing returns the desired string.
1689 val asprintf : ('a, formatter, unit, string) format4 -> 'a
1693 Same as printf above, but instead of printing on a formatter, returns a
1695 string containing the result of formatting the arguments. The type of
1696 asprintf is general enough to interact nicely with %a conversions.
1697 Since 4.01.0
1700 val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
1704 Same as Format.fprintf , except the formatter is the last argument.
1706 dprintf "..." a b c is a function of type formatter -> unit which can
1707 be given to a format specifier %t .
1708 This can be used as a replacement for Format.asprintf to delay format‐
1710 ting decisions. Using the string returned by Format.asprintf in a for‐
1711 matting context forces formatting decisions to be taken in isolation,
1712 and the final string may be created prematurely. Format.dprintf allows
1713 delay of formatting decisions until the final formatting context is
1714 known. For example:
1715 let t = Format.dprintf "%i@ %i@ %i" 1 2 3 in
1716 ...
1717 Format.printf "@[<v>%t@]" t
1718 Since 4.08.0
1722 val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
1726 Same as fprintf above, but does not print anything. Useful to ignore
1728 some material when conditionally printing.
1729 Since 3.10.0
1732 Formatted Pretty-Printing with continuations.
1737 val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1739 'a) format4 -> 'b
1740 Same as fprintf above, but instead of returning immediately, passes the
1742 formatter to its first argument at the end of printing.
1743 val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a)
1747 format4 -> 'b
1748 Same as Format.dprintf above, but instead of returning immediately,
1750 passes the suspended printer to its first argument at the end of print‐
1751 ing.
1752 Since 4.08.0
1755 val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1759 'a) format4 -> 'b
1760 Same as kfprintf above, but does not print anything. Useful to ignore
1762 some material when conditionally printing.
1763 Since 3.12.0
1766 val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1770 Same as sprintf above, but instead of returning the string, passes it
1772 to the first argument.
1773 val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 ->
1777 'b
1778 Same as asprintf above, but instead of returning the string, passes it
1780 to the first argument.
1781 Since 4.03
1784 Deprecated
1789 val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
1790 Deprecated. This function is error prone. Do not use it. This func‐
1792 tion is neither compositional nor incremental, since it flushes the
1793 pretty-printer queue at each call.
1794 If you need to print to some buffer b , you must first define a format‐
1796 ter writing to b , using let to_b = formatter_of_buffer b ; then use
1797 regular calls to Format.fprintf with formatter to_b .
1798 val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1802 Deprecated. An alias for ksprintf .
1804 val set_all_formatter_output_functions : out:(string -> int -> int ->
1808 unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int
1809 -> unit) -> unit
1810 Deprecated. Subsumed by set_formatter_out_functions .
1812 val get_all_formatter_output_functions : unit -> (string -> int -> int
1816 -> unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
1817 Deprecated. Subsumed by get_formatter_out_functions .
1819 val pp_set_all_formatter_output_functions : formatter -> out:(string ->
1823 int -> int -> unit) -> flush:(unit -> unit) -> newline:(unit -> unit)
1824 -> spaces:(int -> unit) -> unit
1825 Deprecated. Subsumed by pp_set_formatter_out_functions .
1827 val pp_get_all_formatter_output_functions : formatter -> unit ->
1831 (string -> int -> int -> unit) * (unit -> unit) * (unit -> unit) * (int
1832 -> unit)
1833 Deprecated. Subsumed by pp_get_formatter_out_functions .
1835 String tags
1840 val pp_open_tag : formatter -> tag -> unit
1841 Deprecated. Subsumed by Format.pp_open_stag .
1843 val open_tag : tag -> unit
1847 Deprecated. Subsumed by Format.open_stag .
1849 val pp_close_tag : formatter -> unit -> unit
1853 Deprecated. Subsumed by Format.pp_close_stag .
1855 val close_tag : unit -> unit
1859 Deprecated. Subsumed by Format.close_stag .
1861 type formatter_tag_functions = {
1864 mark_open_tag : tag -> string ;
1865 mark_close_tag : tag -> string ;
1866 print_open_tag : tag -> unit ;
1867 print_close_tag : tag -> unit ;
1868 }
1869 Deprecated. Subsumed by Format.formatter_stag_functions .
1872 val pp_set_formatter_tag_functions : formatter -> formatter_tag_func‐
1876 tions -> unit
1877 Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
1879 This function will erase non-string tag formatting functions.
1882 val set_formatter_tag_functions : formatter_tag_functions -> unit
1886 Deprecated. Subsumed by Format.set_formatter_stag_functions .
1888 val pp_get_formatter_tag_functions : formatter -> unit -> format‐
1892 ter_tag_functions
1893 Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
1895 val get_formatter_tag_functions : unit -> formatter_tag_functions
1899 Deprecated. Subsumed by Format.get_formatter_stag_functions .
1901OCamldoc 2020-09-01 Format(3)