1Stdlib.Format(3) OCaml library Stdlib.Format(3)
2
6 Stdlib.Format - no description
7
9 Module Stdlib.Format
10
12 Module Format
13 : (module Stdlib__format)
14 Introduction
24 For a gentle introduction to the basics of pretty-printing using Format
25 , read http://caml.inria.fr/resources/doc/guides/format.en.html.
26 You may consider this module as providing an extension to the printf
28 facility to provide automatic line splitting. The addition of
29 pretty-printing annotations to your regular printf format strings gives
30 you fancy indentation and line breaks. Pretty-printing annotations are
31 described below in the documentation of the function Format.fprintf .
32 You may also use the explicit pretty-printing box management and print‐
34 ing functions provided by this module. This style is more basic but
35 more verbose than the concise fprintf format strings.
36 For instance, the sequence open_box 0; print_string "x ="; print_space
38 ();
39 print_int 1; close_box (); print_newline () that prints x = 1
40 within a pretty-printing box, can be abbreviated as printf "@[%s@
41 %i@]@." "x =" 1 , or even shorter printf "@[x =@ %i@]@." 1 .
42 Rule of thumb for casual users of this library:
44 -use simple pretty-printing boxes (as obtained by open_box 0 );
46 -use simple break hints as obtained by print_cut () that outputs a sim‐
48 ple break hint, or by print_space () that outputs a space indicating a
49 break hint;
50 -once a pretty-printing box is open, display its material with basic
52 printing functions (e. g. print_int and print_string );
53 -when the material for a pretty-printing box has been printed, call
55 close_box () to close the box;
56 -at the end of pretty-printing, flush the pretty-printer to display all
58 the remaining material, e.g. evaluate print_newline () .
59 The behavior of pretty-printing commands is unspecified if there is no
61 open pretty-printing box. Each box opened by one of the open_ functions
62 below must be closed using close_box for proper formatting. Otherwise,
63 some of the material printed in the boxes may not be output, or may be
64 formatted incorrectly.
65 In case of interactive use, each phrase is executed in the initial
67 state of the standard pretty-printer: after each phrase execution, the
68 interactive system closes all open pretty-printing boxes, flushes all
69 pending text, and resets the standard pretty-printer.
70 Warning: mixing calls to pretty-printing functions of this module with
72 calls to Stdlib low level output functions is error prone.
73 The pretty-printing functions output material that is delayed in the
75 pretty-printer queue and stacks in order to compute proper line split‐
76 ting. In contrast, basic I/O output functions write directly in their
77 output device. As a consequence, the output of a basic I/O function may
78 appear before the output of a pretty-printing function that has been
79 called before. For instance,
80 Stdlib.print_string "<";
81 Format.print_string "PRETTY";
82 Stdlib.print_string ">";
83 Format.print_string "TEXT";
84 leads to output <>PRETTYTEXT .
85 type formatter
87 Abstract data corresponding to a pretty-printer (also called a format‐
90 ter) and all its machinery. See also Format.formatter .
91 Pretty-printing boxes
96 The pretty-printing engine uses the concepts of pretty-printing box and
97 break hint to drive indentation and line splitting behavior of the
98 pretty-printer.
99 Each different pretty-printing box kind introduces a specific line
101 splitting policy:
102 -within an horizontal box, break hints never split the line (but the
105 line may be split in a box nested deeper),
106 -within a vertical box, break hints always split the line,
108 -within an horizontal/vertical box, if the box fits on the current line
110 then break hints never split the line, otherwise break hint always
111 split the line,
112 -within a compacting box, a break hint never splits the line, unless
114 there is no more room on the current line.
115 Note that line splitting policy is box specific: the policy of a box
117 does not rule the policy of inner boxes. For instance, if a vertical
118 box is nested in an horizontal box, all break hints within the vertical
119 box will split the line.
120 Moreover, opening a box after the Format.maxindent splits the line
122 whether or not the box would end up fitting on the line.
123 val pp_open_box : formatter -> int -> unit
125 val open_box : int -> unit
130 pp_open_box ppf d opens a new compacting pretty-printing box with off‐
133 set d in the formatter ppf .
134 Within this box, the pretty-printer prints as much as possible material
136 on every line.
137 A break hint splits the line if there is no more room on the line to
139 print the remainder of the box.
140 Within this box, the pretty-printer emphasizes the box structure: if a
142 structural box does not fit fully on a simple line, a break hint also
143 splits the line if the splitting ``moves to the left'' (i.e. the new
144 line gets an indentation smaller than the one of the current line).
145 This box is the general purpose pretty-printing box.
147 If the pretty-printer splits the line in the box, offset d is added to
149 the current indentation.
150 val pp_close_box : formatter -> unit -> unit
154 val close_box : unit -> unit
159 Closes the most recently open pretty-printing box.
161 val pp_open_hbox : formatter -> unit -> unit
165 val open_hbox : unit -> unit
170 pp_open_hbox ppf () opens a new 'horizontal' pretty-printing box.
173 This box prints material on a single line.
175 Break hints in a horizontal box never split the line. (Line splitting
177 may still occur inside boxes nested deeper).
178 val pp_open_vbox : formatter -> int -> unit
182 val open_vbox : int -> unit
187 pp_open_vbox ppf d opens a new 'vertical' pretty-printing box with off‐
190 set d .
191 This box prints material on as many lines as break hints in the box.
193 Every break hint in a vertical box splits the line.
195 If the pretty-printer splits the line in the box, d is added to the
197 current indentation.
198 val pp_open_hvbox : formatter -> int -> unit
202 val open_hvbox : int -> unit
207 pp_open_hvbox ppf d opens a new 'horizontal/vertical' pretty-printing
210 box with offset d .
211 This box behaves as an horizontal box if it fits on a single line, oth‐
213 erwise it behaves as a vertical box.
214 If the pretty-printer splits the line in the box, d is added to the
216 current indentation.
217 val pp_open_hovbox : formatter -> int -> unit
221 val open_hovbox : int -> unit
226 pp_open_hovbox ppf d opens a new 'horizontal-or-vertical' pretty-print‐
229 ing box with offset d .
230 This box prints material as much as possible on every line.
232 A break hint splits the line if there is no more room on the line to
234 print the remainder of the box.
235 If the pretty-printer splits the line in the box, d is added to the
237 current indentation.
238 Formatting functions
243 val pp_print_string : formatter -> string -> unit
244 val print_string : string -> unit
249 pp_print_string ppf s prints s in the current pretty-printing box.
252 val pp_print_as : formatter -> int -> string -> unit
256 val print_as : int -> string -> unit
261 pp_print_as ppf len s prints s in the current pretty-printing box. The
264 pretty-printer formats s as if it were of length len .
265 val pp_print_int : formatter -> int -> unit
269 val print_int : int -> unit
274 Print an integer in the current pretty-printing box.
276 val pp_print_float : formatter -> float -> unit
280 val print_float : float -> unit
285 Print a floating point number in the current pretty-printing box.
287 val pp_print_char : formatter -> char -> unit
291 val print_char : char -> unit
296 Print a character in the current pretty-printing box.
298 val pp_print_bool : formatter -> bool -> unit
302 val print_bool : bool -> unit
307 Print a boolean in the current pretty-printing box.
309 Break hints
314 A 'break hint' tells the pretty-printer to output some space or split
315 the line whichever way is more appropriate to the current pretty-print‐
316 ing box splitting rules.
317 Break hints are used to separate printing items and are mandatory to
319 let the pretty-printer correctly split lines and indent items.
320 Simple break hints are:
322 -the 'space': output a space or split the line if appropriate,
324 -the 'cut': split the line if appropriate.
326 Note: the notions of space and line splitting are abstract for the
328 pretty-printing engine, since those notions can be completely redefined
329 by the programmer. However, in the pretty-printer default setting,
330 ``output a space'' simply means printing a space character (ASCII code
331 32) and ``split the line'' means printing a newline character (ASCII
332 code 10).
333 val pp_print_space : formatter -> unit -> unit
335 val print_space : unit -> unit
340 pp_print_space ppf () emits a 'space' break hint: the pretty-printer
343 may split the line at this point, otherwise it prints one space.
344 pp_print_space ppf () is equivalent to pp_print_break ppf 1 0 .
347 val pp_print_cut : formatter -> unit -> unit
351 val print_cut : unit -> unit
356 pp_print_cut ppf () emits a 'cut' break hint: the pretty-printer may
359 split the line at this point, otherwise it prints nothing.
360 pp_print_cut ppf () is equivalent to pp_print_break ppf 0 0 .
363 val pp_print_break : formatter -> int -> int -> unit
367 val print_break : int -> int -> unit
372 pp_print_break ppf nspaces offset emits a 'full' break hint: the
375 pretty-printer may split the line at this point, otherwise it prints
376 nspaces spaces.
377 If the pretty-printer splits the line, offset is added to the current
379 indentation.
380 val pp_print_custom_break : formatter -> fits:string * int * string ->
384 breaks:string * int * string -> unit
385 pp_print_custom_break ppf ~fits:(s1, n, s2) ~breaks:(s3, m, s4) emits a
388 custom break hint: the pretty-printer may split the line at this point.
389 If it does not split the line, then the s1 is emitted, then n spaces,
391 then s2 .
392 If it splits the line, then it emits the s3 string, then an indent
394 (according to the box rules), then an offset of m spaces, then the s4
395 string.
396 While n and m are handled by formatter_out_functions.out_indent , the
398 strings will be handled by formatter_out_functions.out_string . This
399 allows for a custom formatter that handles indentation distinctly, for
400 example, outputs <br/> tags or entities.
401 The custom break is useful if you want to change which visible
403 (non-whitespace) characters are printed in case of break or no break.
404 For example, when printing a list
405 [a; b; c]
406 trailing semicolon when it is printed vertically:
407 [
410 a;
411 b;
412 c;
413 ]
414 You can do this as follows:
417 printf "@[<v 0>[@;<0 2>@[<v 0>a;@,b;@,c@]%t]@]@\n"
418 (pp_print_custom_break ~fits:("", 0, "") ~breaks:(";", 0, ""))
419 Since 4.08.0
423 val pp_force_newline : formatter -> unit -> unit
427 val force_newline : unit -> unit
432 Force a new line in the current pretty-printing box.
434 The pretty-printer must split the line at this point,
436 Not the normal way of pretty-printing, since imperative line splitting
438 may interfere with current line counters and box size calculation.
439 Using break hints within an enclosing vertical box is a better alterna‐
440 tive.
441 val pp_print_if_newline : formatter -> unit -> unit
445 val print_if_newline : unit -> unit
450 Execute the next formatting command if the preceding line has just been
452 split. Otherwise, ignore the next formatting command.
453 Pretty-printing termination
458 val pp_print_flush : formatter -> unit -> unit
459 val print_flush : unit -> unit
464 End of pretty-printing: resets the pretty-printer to initial state.
466 All open pretty-printing boxes are closed, all pending text is printed.
468 In addition, the pretty-printer low level output device is flushed to
469 ensure that all pending text is really displayed.
470 Note: never use print_flush in the normal course of a pretty-printing
472 routine, since the pretty-printer uses a complex buffering machinery to
473 properly indent the output; manually flushing those buffers at random
474 would conflict with the pretty-printer strategy and result to poor ren‐
475 dering.
476 Only consider using print_flush when displaying all pending material is
478 mandatory (for instance in case of interactive use when you want the
479 user to read some text) and when resetting the pretty-printer state
480 will not disturb further pretty-printing.
481 Warning: If the output device of the pretty-printer is an output chan‐
483 nel, repeated calls to print_flush means repeated calls to flush to
484 flush the out channel; these explicit flush calls could foil the
485 buffering strategy of output channels and could dramatically impact
486 efficiency.
487 val pp_print_newline : formatter -> unit -> unit
491 val print_newline : unit -> unit
496 End of pretty-printing: resets the pretty-printer to initial state.
498 All open pretty-printing boxes are closed, all pending text is printed.
500 Equivalent to Format.print_flush followed by a new line. See corre‐
502 sponding words of caution for Format.print_flush .
503 Note: this is not the normal way to output a new line; the preferred
505 method is using break hints within a vertical pretty-printing box.
506 Margin
511 val pp_set_margin : formatter -> int -> unit
512 val set_margin : int -> unit
517 pp_set_margin ppf d sets the right margin to d (in characters): the
520 pretty-printer splits lines that overflow the right margin according to
521 the break hints given. Setting the margin to d means that the format‐
522 ting engine aims at printing at most d-1 characters per line. Nothing
523 happens if d is smaller than 2. If d is too large, the right margin is
524 set to the maximum admissible value (which is greater than 10 ^ 9 ).
525 If d is less than the current maximum indentation limit, the maximum
526 indentation limit is decreased while trying to preserve a minimal ratio
527 max_indent/margin>=50% and if possible the current difference margin -
528 max_indent .
529 See also Format.pp_set_geometry .
531 val pp_get_margin : formatter -> unit -> int
535 val get_margin : unit -> int
540 Returns the position of the right margin.
542 Maximum indentation limit
547 val pp_set_max_indent : formatter -> int -> unit
548 val set_max_indent : int -> unit
553 pp_set_max_indent ppf d sets the maximum indentation limit of lines to
556 d (in characters): once this limit is reached, new pretty-printing
557 boxes are rejected to the left, unless the enclosing box fully fits on
558 the current line. As an illustration,
559 set_margin 10; set_max_indent 5; printf "@[123456@[7@]89A@]@."
560 yields
561 123456
562 789A
563 because the nested box "@[7@]" is opened after the maximum indentation
565 limit ( 7>5 ) and its parent box does not fit on the current line.
566 Either decreasing the length of the parent box to make it fit on a
567 line:
568 printf "@[123456@[7@]89@]@."
569 or opening an intermediary box before the maximum indentation limit
570 which fits on the current line
571 printf "@[123@[456@[7@]89@]A@]@."
572 avoids the rejection to the left of the inner boxes and print respec‐
573 tively "123456789" and "123456789A" . Note also that vertical boxes
574 never fit on a line whereas horizontal boxes always fully fit on the
575 current line. Opening a box may split a line whereas the contents may
576 have fit. If this behavior is problematic, it can be curtailed by set‐
577 ting the maximum indentation limit to margin - 1 . Note that setting
578 the maximum indentation limit to margin is invalid.
579 Nothing happens if d is smaller than 2.
581 If d is too large, the limit is set to the maximum admissible value
583 (which is greater than 10 ^ 9 ).
584 If d is greater or equal than the current margin, it is ignored, and
586 the current maximum indentation limit is kept.
587 See also Format.pp_set_geometry .
589 val pp_get_max_indent : formatter -> unit -> int
593 val get_max_indent : unit -> int
598 Return the maximum indentation limit (in characters).
600 Geometry
605 Geometric functions can be used to manipulate simultaneously the cou‐
606 pled variables, margin and maxixum indentation limit.
607 type geometry = {
609 max_indent : int ;
610 margin : int ;
611 }
612 val check_geometry : geometry -> bool
618 Check if the formatter geometry is valid: 1 < max_indent < margin
620 val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
625 val set_geometry : max_indent:int -> margin:int -> unit
630 val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int ->
635 unit
636 val safe_set_geometry : max_indent:int -> margin:int -> unit
641 pp_set_geometry ppf ~max_indent ~margin sets both the margin and maxi‐
644 mum indentation limit for ppf .
645 When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin
647 is equivalent to pp_set_margin ppf margin; pp_set_max_indent ppf
648 max_indent ; and avoids the subtly incorrect pp_set_max_indent ppf
649 max_indent; pp_set_margin ppf margin ;
650 Outside of this domain, pp_set_geometry raises an invalid argument
652 exception whereas pp_safe_set_geometry does nothing.
653 Since 4.08.0
656 val pp_update_geometry : formatter -> (geometry -> geometry) -> unit
660 pp_update_geometry ppf (fun geo -> { geo with ... }) lets you update a
663 formatter's geometry in a way that is robust to extension of the geome‐
664 try record with new fields.
665 Raises an invalid argument exception if the returned geometry does not
667 satisfy Format.check_geometry .
668 Since 4.11.0
671 val update_geometry : (geometry -> geometry) -> unit
675 val pp_get_geometry : formatter -> unit -> geometry
680 val get_geometry : unit -> geometry
685 Return the current geometry of the formatter
687 Since 4.08.0
690 Maximum formatting depth
695 The maximum formatting depth is the maximum number of pretty-printing
696 boxes simultaneously open.
697 Material inside boxes nested deeper is printed as an ellipsis (more
699 precisely as the text returned by Format.get_ellipsis_text () ).
700 val pp_set_max_boxes : formatter -> int -> unit
702 val set_max_boxes : int -> unit
707 pp_set_max_boxes ppf max sets the maximum number of pretty-printing
710 boxes simultaneously open.
711 Material inside boxes nested deeper is printed as an ellipsis (more
713 precisely as the text returned by Format.get_ellipsis_text () ).
714 Nothing happens if max is smaller than 2.
716 val pp_get_max_boxes : formatter -> unit -> int
720 val get_max_boxes : unit -> int
725 Returns the maximum number of pretty-printing boxes allowed before
727 ellipsis.
728 val pp_over_max_boxes : formatter -> unit -> bool
732 val over_max_boxes : unit -> bool
737 Tests if the maximum number of pretty-printing boxes allowed have
739 already been opened.
740 Tabulation boxes
745 A tabulation box prints material on lines divided into cells of fixed
746 length. A tabulation box provides a simple way to display vertical col‐
747 umns of left adjusted text.
748 This box features command set_tab to define cell boundaries, and com‐
750 mand print_tab to move from cell to cell and split the line when there
751 is no more cells to print on the line.
752 Note: printing within tabulation box is line directed, so arbitrary
754 line splitting inside a tabulation box leads to poor rendering. Yet,
755 controlled use of tabulation boxes allows simple printing of columns
756 within module Format .
757 val pp_open_tbox : formatter -> unit -> unit
759 val open_tbox : unit -> unit
764 open_tbox () opens a new tabulation box.
767 This box prints lines separated into cells of fixed width.
769 Inside a tabulation box, special tabulation markers defines points of
771 interest on the line (for instance to delimit cell boundaries). Func‐
772 tion Format.set_tab sets a tabulation marker at insertion point.
773 A tabulation box features specific tabulation breaks to move to next
775 tabulation marker or split the line. Function Format.print_tbreak
776 prints a tabulation break.
777 val pp_close_tbox : formatter -> unit -> unit
781 val close_tbox : unit -> unit
786 Closes the most recently opened tabulation box.
788 val pp_set_tab : formatter -> unit -> unit
792 val set_tab : unit -> unit
797 Sets a tabulation marker at current insertion point.
799 val pp_print_tab : formatter -> unit -> unit
803 val print_tab : unit -> unit
808 print_tab () emits a 'next' tabulation break hint: if not already set
811 on a tabulation marker, the insertion point moves to the first tabula‐
812 tion marker on the right, or the pretty-printer splits the line and
813 insertion point moves to the leftmost tabulation marker.
814 It is equivalent to print_tbreak 0 0 .
816 val pp_print_tbreak : formatter -> int -> int -> unit
820 val print_tbreak : int -> int -> unit
825 print_tbreak nspaces offset emits a 'full' tabulation break hint.
828 If not already set on a tabulation marker, the insertion point moves to
830 the first tabulation marker on the right and the pretty-printer prints
831 nspaces spaces.
832 If there is no next tabulation marker on the right, the pretty-printer
834 splits the line at this point, then insertion point moves to the left‐
835 most tabulation marker of the box.
836 If the pretty-printer splits the line, offset is added to the current
838 indentation.
839 Ellipsis
844 val pp_set_ellipsis_text : formatter -> string -> unit
845 val set_ellipsis_text : string -> unit
850 Set the text of the ellipsis printed when too many pretty-printing
852 boxes are open (a single dot, . , by default).
853 val pp_get_ellipsis_text : formatter -> unit -> string
857 val get_ellipsis_text : unit -> string
862 Return the text of the ellipsis.
864 Semantic tags
869 type stag = ..
870 Semantic tags (or simply tags) are user's defined annotations to asso‐
873 ciate user's specific operations to printed entities.
874 Common usage of semantic tags is text decoration to get specific font
876 or text size rendering for a display device, or marking delimitation of
877 entities (e.g. HTML or TeX elements or terminal escape sequences).
878 More sophisticated usage of semantic tags could handle dynamic modifi‐
879 cation of the pretty-printer behavior to properly print the material
880 within some specific tags. For instance, we can define an RGB tag like
881 so:
882 type stag += RGB of {r:int;g:int;b:int}
883 In order to properly delimit printed entities, a semantic tag must be
886 opened before and closed after the entity. Semantic tags must be prop‐
887 erly nested like parentheses using Format.pp_open_stag and For‐
888 mat.pp_close_stag .
889 Tag specific operations occur any time a tag is opened or closed, At
891 each occurrence, two kinds of operations are performed tag-marking and
892 tag-printing:
893 -The tag-marking operation is the simpler tag specific operation: it
895 simply writes a tag specific string into the output device of the for‐
896 matter. Tag-marking does not interfere with line-splitting computation.
897 -The tag-printing operation is the more involved tag specific opera‐
899 tion: it can print arbitrary material to the formatter. Tag-printing is
900 tightly linked to the current pretty-printer operations.
901 Roughly speaking, tag-marking is commonly used to get a better render‐
903 ing of texts in the rendering device, while tag-printing allows fine
904 tuning of printing routines to print the same entity differently
905 according to the semantic tags (i.e. print additional material or even
906 omit parts of the output).
907 More precisely: when a semantic tag is opened or closed then both and
909 successive 'tag-printing' and 'tag-marking' operations occur:
910 -Tag-printing a semantic tag means calling the formatter specific func‐
912 tion print_open_stag (resp. print_close_stag ) with the name of the
913 tag as argument: that tag-printing function can then print any regular
914 material to the formatter (so that this material is enqueued as usual
915 in the formatter queue for further line splitting computation).
916 -Tag-marking a semantic tag means calling the formatter specific func‐
918 tion mark_open_stag (resp. mark_close_stag ) with the name of the tag
919 as argument: that tag-marking function can then return the 'tag-opening
920 marker' (resp. `tag-closing marker') for direct output into the output
921 device of the formatter.
922 Being written directly into the output device of the formatter, seman‐
924 tic tag marker strings are not considered as part of the printing mate‐
925 rial that drives line splitting (in other words, the length of the
926 strings corresponding to tag markers is considered as zero for line
927 splitting).
928 Thus, semantic tag handling is in some sense transparent to
930 pretty-printing and does not interfere with usual indentation. Hence, a
931 single pretty-printing routine can output both simple 'verbatim' mate‐
932 rial or richer decorated output depending on the treatment of tags. By
933 default, tags are not active, hence the output is not decorated with
934 tag information. Once set_tags is set to true , the pretty-printer
935 engine honors tags and decorates the output accordingly.
936 Default tag-marking functions behave the HTML way: Format.tag are
938 enclosed in "<" and ">" while other tags are ignored; hence, opening
939 marker for tag string "t" is "<t>" and closing marker is "</t>" .
940 Default tag-printing functions just do nothing.
942 Tag-marking and tag-printing functions are user definable and can be
944 set by calling Format.set_formatter_stag_functions .
945 Semantic tag operations may be set on or off with Format.set_tags .
947 Tag-marking operations may be set on or off with Format.set_mark_tags .
948 Tag-printing operations may be set on or off with Format.set_print_tags
949 .
950 type tag = string
953 type Format.stag +=
958 | String_tag of tag (* String_tag s is a string tag s . String tags
959 can be inserted either by explicitly using the constructor String_tag
960 or by using the dedicated format syntax "@{<s> ... @}" .
961 *)
962 val pp_open_stag : formatter -> stag -> unit
968 val open_stag : stag -> unit
973 pp_open_stag ppf t opens the semantic tag named t .
976 The print_open_stag tag-printing function of the formatter is called
978 with t as argument; then the opening tag marker for t , as given by
979 mark_open_stag t , is written into the output device of the formatter.
980 val pp_close_stag : formatter -> unit -> unit
984 val close_stag : unit -> unit
989 pp_close_stag ppf () closes the most recently opened semantic tag t .
992 The closing tag marker, as given by mark_close_stag t , is written into
994 the output device of the formatter; then the print_close_stag
995 tag-printing function of the formatter is called with t as argument.
996 val pp_set_tags : formatter -> bool -> unit
1000 val set_tags : bool -> unit
1005 pp_set_tags ppf b turns on or off the treatment of semantic tags
1008 (default is off).
1009 val pp_set_print_tags : formatter -> bool -> unit
1013 val set_print_tags : bool -> unit
1018 pp_set_print_tags ppf b turns on or off the tag-printing operations.
1021 val pp_set_mark_tags : formatter -> bool -> unit
1025 val set_mark_tags : bool -> unit
1030 pp_set_mark_tags ppf b turns on or off the tag-marking operations.
1033 val pp_get_print_tags : formatter -> unit -> bool
1037 val get_print_tags : unit -> bool
1042 Return the current status of tag-printing operations.
1044 val pp_get_mark_tags : formatter -> unit -> bool
1048 val get_mark_tags : unit -> bool
1053 Return the current status of tag-marking operations.
1055 val pp_set_formatter_out_channel : formatter -> out_channel -> unit
1059 Redirecting the standard formatter output
1062 val set_formatter_out_channel : out_channel -> unit
1063 Redirect the standard pretty-printer output to the given channel. (All
1065 the output functions of the standard formatter are set to the default
1066 output functions printing to the given channel.)
1067 set_formatter_out_channel is equivalent to Format.pp_set_format‐
1070 ter_out_channel std_formatter .
1071 val pp_set_formatter_output_functions : formatter -> (string -> int ->
1075 int -> unit) -> (unit -> unit) -> unit
1076 val set_formatter_output_functions : (string -> int -> int -> unit) ->
1081 (unit -> unit) -> unit
1082 pp_set_formatter_output_functions ppf out flush redirects the standard
1085 pretty-printer output functions to the functions out and flush .
1086 The out function performs all the pretty-printer string output. It is
1088 called with a string s , a start position p , and a number of charac‐
1089 ters n ; it is supposed to output characters p to p + n - 1 of s .
1090 The flush function is called whenever the pretty-printer is flushed
1092 (via conversion %! , or pretty-printing indications @? or @. , or
1093 using low level functions print_flush or print_newline ).
1094 val pp_get_formatter_output_functions : formatter -> unit -> (string ->
1098 int -> int -> unit) * (unit -> unit)
1099 val get_formatter_output_functions : unit -> (string -> int -> int ->
1104 unit) * (unit -> unit)
1105 Return the current output functions of the standard pretty-printer.
1107 Redefining formatter output
1112 The Format module is versatile enough to let you completely redefine
1113 the meaning of pretty-printing output: you may provide your own func‐
1114 tions to define how to handle indentation, line splitting, and even
1115 printing of all the characters that have to be printed!
1116 Redefining output functions
1118 type formatter_out_functions = {
1119 out_string : string -> int -> int -> unit ;
1120 out_flush : unit -> unit ;
1121 out_newline : unit -> unit ;
1122 out_spaces : int -> unit ;
1123 out_indent : int -> unit ;
1124 }
1125 The set of output functions specific to a formatter:
1128 -the out_string function performs all the pretty-printer string output.
1130 It is called with a string s , a start position p , and a number of
1131 characters n ; it is supposed to output characters p to p + n - 1 of s
1132 .
1133 -the out_flush function flushes the pretty-printer output device.
1135 - out_newline is called to open a new line when the pretty-printer
1137 splits the line.
1138 -the out_spaces function outputs spaces when a break hint leads to spa‐
1140 ces instead of a line split. It is called with the number of spaces to
1141 output.
1142 -the out_indent function performs new line indentation when the
1144 pretty-printer splits the line. It is called with the indentation value
1145 of the new line.
1146 By default:
1148 -fields out_string and out_flush are output device specific; (e.g.
1150 output_string and flush for a out_channel device, or Buffer.add_sub‐
1151 string and ignore for a Buffer.t output device),
1152 -field out_newline is equivalent to out_string "\n" 0 1 ;
1154 -fields out_spaces and out_indent are equivalent to out_string
1156 (String.make n ' ') 0 n .
1157 Since 4.01.0
1161 val pp_set_formatter_out_functions : formatter -> formatter_out_func‐
1165 tions -> unit
1166 val set_formatter_out_functions : formatter_out_functions -> unit
1171 pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer
1174 output functions of ppf to those of argument out_funs ,
1175 This way, you can change the meaning of indentation (which can be some‐
1177 thing else than just printing space characters) and the meaning of new
1178 lines opening (which can be connected to any other action needed by the
1179 application at hand).
1180 Reasonable defaults for functions out_spaces and out_newline are
1182 respectively out_funs.out_string (String.make n ' ') 0 n and
1183 out_funs.out_string "\n" 0 1 .
1184 Since 4.01.0
1187 val pp_get_formatter_out_functions : formatter -> unit -> format‐
1191 ter_out_functions
1192 val get_formatter_out_functions : unit -> formatter_out_functions
1197 Return the current output functions of the pretty-printer, including
1199 line splitting and indentation functions. Useful to record the current
1200 setting and restore it afterwards.
1201 Since 4.01.0
1204 Redefining semantic tag operations
1209 type formatter_stag_functions = {
1210 mark_open_stag : stag -> string ;
1211 mark_close_stag : stag -> string ;
1212 print_open_stag : stag -> unit ;
1213 print_close_stag : stag -> unit ;
1214 }
1215 The semantic tag handling functions specific to a formatter: mark ver‐
1218 sions are the 'tag-marking' functions that associate a string marker to
1219 a tag in order for the pretty-printing engine to write those markers as
1220 0 length tokens in the output device of the formatter. print versions
1221 are the 'tag-printing' functions that can perform regular printing when
1222 a tag is closed or opened.
1223 val pp_set_formatter_stag_functions : formatter -> formatter_stag_func‐
1227 tions -> unit
1228 val set_formatter_stag_functions : formatter_stag_functions -> unit
1233 pp_set_formatter_stag_functions ppf tag_funs changes the meaning of
1236 opening and closing semantic tag operations to use the functions in
1237 tag_funs when printing on ppf .
1238 When opening a semantic tag with name t , the string t is passed to the
1240 opening tag-marking function (the mark_open_stag field of the record
1241 tag_funs ), that must return the opening tag marker for that name. When
1242 the next call to close_stag () happens, the semantic tag name t is sent
1243 back to the closing tag-marking function (the mark_close_stag field of
1244 record tag_funs ), that must return a closing tag marker for that name.
1245 The print_ field of the record contains the tag-printing functions that
1247 are called at tag opening and tag closing time, to output regular mate‐
1248 rial in the pretty-printer queue.
1249 val pp_get_formatter_stag_functions : formatter -> unit -> format‐
1253 ter_stag_functions
1254 val get_formatter_stag_functions : unit -> formatter_stag_functions
1259 Return the current semantic tag operation functions of the standard
1261 pretty-printer.
1262 Defining formatters
1267 Defining new formatters permits unrelated output of material in paral‐
1268 lel on several output devices. All the parameters of a formatter are
1269 local to the formatter: right margin, maximum indentation limit, maxi‐
1270 mum number of pretty-printing boxes simultaneously open, ellipsis, and
1271 so on, are specific to each formatter and may be fixed independently.
1272 For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b
1274 returns a new formatter using buffer b as its output device. Simi‐
1275 larly, given a out_channel output channel oc , Format.format‐
1276 ter_of_out_channel oc returns a new formatter using channel oc as its
1277 output device.
1278 Alternatively, given out_funs , a complete set of output functions for
1280 a formatter, then Format.formatter_of_out_functions out_funs computes a
1281 new formatter using those functions for output.
1282 val formatter_of_out_channel : out_channel -> formatter
1284 formatter_of_out_channel oc returns a new formatter writing to the cor‐
1287 responding output channel oc .
1288 val std_formatter : formatter
1292 The standard formatter to write to standard output.
1294 It is defined as Format.formatter_of_out_channel stdout .
1296 val err_formatter : formatter
1300 A formatter to write to standard error.
1302 It is defined as Format.formatter_of_out_channel stderr .
1304 val formatter_of_buffer : Buffer.t -> formatter
1308 formatter_of_buffer b returns a new formatter writing to buffer b . At
1311 the end of pretty-printing, the formatter must be flushed using For‐
1312 mat.pp_print_flush or Format.pp_print_newline , to print all the pend‐
1313 ing material into the buffer.
1314 val stdbuf : Buffer.t
1318 The string buffer in which str_formatter writes.
1320 val str_formatter : formatter
1324 A formatter to output to the Format.stdbuf string buffer.
1326 str_formatter is defined as Format.formatter_of_buffer Format.stdbuf .
1329 val flush_str_formatter : unit -> string
1333 Returns the material printed with str_formatter , flushes the formatter
1335 and resets the corresponding buffer.
1336 val make_formatter : (string -> int -> int -> unit) -> (unit -> unit)
1340 -> formatter
1341 make_formatter out flush returns a new formatter that outputs with
1344 function out , and flushes with function flush .
1345 For instance,
1347 make_formatter
1348 (Stdlib.output oc)
1349 (fun () -> Stdlib.flush oc)
1350 returns a formatter to the out_channel oc .
1351 val formatter_of_out_functions : formatter_out_functions -> formatter
1355 formatter_of_out_functions out_funs returns a new formatter that writes
1358 with the set of output functions out_funs .
1359 See definition of type Format.formatter_out_functions for the meaning
1361 of argument out_funs .
1362 Since 4.06.0
1365 Symbolic pretty-printing
1370 Symbolic pretty-printing is pretty-printing using a symbolic formatter,
1371 i.e. a formatter that outputs symbolic pretty-printing items.
1372 When using a symbolic formatter, all regular pretty-printing activities
1374 occur but output material is symbolic and stored in a buffer of output
1375 items. At the end of pretty-printing, flushing the output buffer
1376 allows post-processing of symbolic output before performing low level
1377 output operations.
1378 In practice, first define a symbolic output buffer b using:
1380 - let sob = make_symbolic_output_buffer () . Then define a symbolic
1382 formatter with:
1383 - let ppf = formatter_of_symbolic_output_buffer sob
1385 Use symbolic formatter ppf as usual, and retrieve symbolic items at end
1387 of pretty-printing by flushing symbolic output buffer sob with:
1388 - flush_symbolic_output_buffer sob .
1390 type symbolic_output_item =
1393 | Output_flush (* symbolic flush command
1394 *)
1395 | Output_newline (* symbolic newline command
1396 *)
1397 | Output_string of string
1398 (* Output_string s : symbolic output for string s
1399 *)
1401 | Output_spaces of int
1402 (* Output_spaces n : symbolic command to output n spaces
1403 *)
1404 | Output_indent of int
1405 (* Output_indent i : symbolic indentation of size i
1406 *)
1408 Items produced by symbolic pretty-printers
1411 Since 4.06.0
1414 type symbolic_output_buffer
1417 The output buffer of a symbolic pretty-printer.
1420 Since 4.06.0
1423 val make_symbolic_output_buffer : unit -> symbolic_output_buffer
1427 make_symbolic_output_buffer () returns a fresh buffer for symbolic out‐
1430 put.
1431 Since 4.06.0
1434 val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
1438 clear_symbolic_output_buffer sob resets buffer sob .
1441 Since 4.06.0
1444 val get_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1448 bolic_output_item list
1449 get_symbolic_output_buffer sob returns the contents of buffer sob .
1452 Since 4.06.0
1455 val flush_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1459 bolic_output_item list
1460 flush_symbolic_output_buffer sob returns the contents of buffer sob and
1463 resets buffer sob . flush_symbolic_output_buffer sob is equivalent to
1464 let items = get_symbolic_output_buffer sob in
1465 clear_symbolic_output_buffer sob; items
1466 Since 4.06.0
1470 val add_symbolic_output_item : symbolic_output_buffer -> symbolic_out‐
1474 put_item -> unit
1475 add_symbolic_output_item sob itm adds item itm to buffer sob .
1478 Since 4.06.0
1481 val formatter_of_symbolic_output_buffer : symbolic_output_buffer ->
1485 formatter
1486 formatter_of_symbolic_output_buffer sob returns a symbolic formatter
1489 that outputs to symbolic_output_buffer sob .
1490 Since 4.06.0
1493 Convenience formatting functions.
1498 val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter
1499 -> 'a -> unit) -> formatter -> 'a list -> unit
1500 pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to
1503 print each item, and calling pp_sep between items ( pp_sep defaults to
1504 Format.pp_print_cut . Does nothing on empty lists.
1505 Since 4.02.0
1508 val pp_print_text : formatter -> string -> unit
1512 pp_print_text ppf s prints s with spaces and newlines respectively
1515 printed using Format.pp_print_space and Format.pp_force_newline .
1516 Since 4.02.0
1519 val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter
1523 -> 'a -> unit) -> formatter -> 'a option -> unit
1524 pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is
1527 Some v and none if it is None . none prints nothing by default.
1528 Since 4.08
1531 val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter
1535 -> 'e -> unit) -> formatter -> ('a, 'e) result -> unit
1536 pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _
1539 and error if r is Error _ .
1540 Since 4.08
1543 Formatted pretty-printing
1548 Module Format provides a complete set of printf like functions for
1549 pretty-printing using format string specifications.
1550 Specific annotations may be added in the format strings to give
1552 pretty-printing commands to the pretty-printing engine.
1553 Those annotations are introduced in the format strings using the @
1555 character. For instance, @ means a space break, @, means a cut, @[
1556 opens a new box, and @] closes the last open box.
1557 val fprintf : formatter -> ('a, formatter, unit) format -> 'a
1559 fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN accord‐
1565 ing to the format string fmt , and outputs the resulting string on the
1566 formatter ff .
1567 The format string fmt is a character string which contains three types
1569 of objects: plain characters and conversion specifications as specified
1570 in the Printf module, and pretty-printing indications specific to the
1571 Format module.
1572 The pretty-printing indication characters are introduced by a @ charac‐
1574 ter, and their meanings are:
1575 - @[ : open a pretty-printing box. The type and offset of the box may
1577 be optionally specified with the following syntax: the < character,
1578 followed by an optional box type indication, then an optional integer
1579 offset, and the closing > character. Pretty-printing box type is one
1580 of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
1581 pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box,
1582 ' hv ' stands for an 'horizontal/vertical' pretty-printing box, ' b '
1583 stands for an 'horizontal-or-vertical' pretty-printing box demonstrat‐
1584 ing indentation, ' hov ' stands a simple 'horizontal-or-vertical'
1585 pretty-printing box. For instance, @[<hov 2> opens an 'horizon‐
1586 tal-or-vertical' pretty-printing box with indentation 2 as obtained
1587 with open_hovbox 2 . For more details about pretty-printing boxes, see
1588 the various box opening functions open_*box .
1589 - @] : close the most recently opened pretty-printing box.
1591 - @, : output a 'cut' break hint, as with print_cut () .
1593 - @ : output a 'space' break hint, as with print_space () .
1595 - @; : output a 'full' break hint as with print_break . The nspaces and
1597 offset parameters of the break hint may be optionally specified with
1598 the following syntax: the < character, followed by an integer nspaces
1599 value, then an integer offset , and a closing > character. If no
1600 parameters are provided, the good break defaults to a 'space' break
1601 hint.
1602 - @. : flush the pretty-printer and split the line, as with print_new‐
1604 line () .
1605 - @<n> : print the following item as if it were of length n . Hence,
1607 printf "@<0>%s" arg prints arg as a zero length string. If @<n> is not
1608 followed by a conversion specification, then the following character of
1609 the format is printed as if it were of length n .
1610 - @{ : open a semantic tag. The name of the tag may be optionally spec‐
1612 ified with the following syntax: the < character, followed by an
1613 optional string specification, and the closing > character. The string
1614 specification is any character string that does not contain the closing
1615 character '>' . If omitted, the tag name defaults to the empty string.
1616 For more details about semantic tags, see the functions For‐
1617 mat.open_stag and Format.close_stag .
1618 - @} : close the most recently opened semantic tag.
1620 - @? : flush the pretty-printer as with print_flush () . This is
1622 equivalent to the conversion %! .
1623 - @\n : force a newline, as with force_newline () , not the normal way
1625 of pretty-printing, you should prefer using break hints inside a verti‐
1626 cal pretty-printing box.
1627 Note: To prevent the interpretation of a @ character as a pretty-print‐
1629 ing indication, escape it with a % character. Old quotation mode @@ is
1630 deprecated since it is not compatible with formatted input interpreta‐
1631 tion of character '@' .
1632 Example: printf "@[%s@ %d@]@." "x =" 1 is equivalent to open_box ();
1634 print_string "x ="; print_space ();
1635 print_int 1; close_box (); print_newline () . It prints x = 1
1636 within a pretty-printing 'horizontal-or-vertical' box.
1637 val printf : ('a, formatter, unit) format -> 'a
1639 Same as fprintf above, but output on std_formatter .
1641 val eprintf : ('a, formatter, unit) format -> 'a
1645 Same as fprintf above, but output on err_formatter .
1647 val sprintf : ('a, unit, string) format -> 'a
1651 Same as printf above, but instead of printing on a formatter, returns a
1653 string containing the result of formatting the arguments. Note that
1654 the pretty-printer queue is flushed at the end of each call to sprintf
1655 .
1656 In case of multiple and related calls to sprintf to output material on
1658 a single string, you should consider using fprintf with the predefined
1659 formatter str_formatter and call flush_str_formatter () to get the
1660 final result.
1661 Alternatively, you can use Format.fprintf with a formatter writing to a
1663 buffer of your own: flushing the formatter and the buffer at the end of
1664 pretty-printing returns the desired string.
1665 val asprintf : ('a, formatter, unit, string) format4 -> 'a
1669 Same as printf above, but instead of printing on a formatter, returns a
1671 string containing the result of formatting the arguments. The type of
1672 asprintf is general enough to interact nicely with %a conversions.
1673 Since 4.01.0
1676 val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
1680 Same as Format.fprintf , except the formatter is the last argument.
1682 dprintf "..." a b c is a function of type formatter -> unit which can
1683 be given to a format specifier %t .
1684 This can be used as a replacement for Format.asprintf to delay format‐
1686 ting decisions. Using the string returned by Format.asprintf in a for‐
1687 matting context forces formatting decisions to be taken in isolation,
1688 and the final string may be created prematurely. Format.dprintf allows
1689 delay of formatting decisions until the final formatting context is
1690 known. For example:
1691 let t = Format.dprintf "%i@ %i@ %i" 1 2 3 in
1692 ...
1693 Format.printf "@[<v>%t@]" t
1694 Since 4.08.0
1698 val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
1702 Same as fprintf above, but does not print anything. Useful to ignore
1704 some material when conditionally printing.
1705 Since 3.10.0
1708 Formatted Pretty-Printing with continuations.
1713 val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1715 'a) format4 -> 'b
1716 Same as fprintf above, but instead of returning immediately, passes the
1718 formatter to its first argument at the end of printing.
1719 val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a)
1723 format4 -> 'b
1724 Same as Format.dprintf above, but instead of returning immediately,
1726 passes the suspended printer to its first argument at the end of print‐
1727 ing.
1728 Since 4.08.0
1731 val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1735 'a) format4 -> 'b
1736 Same as kfprintf above, but does not print anything. Useful to ignore
1738 some material when conditionally printing.
1739 Since 3.12.0
1742 val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1746 Same as sprintf above, but instead of returning the string, passes it
1748 to the first argument.
1749 val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 ->
1753 'b
1754 Same as asprintf above, but instead of returning the string, passes it
1756 to the first argument.
1757 Since 4.03
1760 Deprecated
1765 val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
1766 Deprecated. This function is error prone. Do not use it. This func‐
1768 tion is neither compositional nor incremental, since it flushes the
1769 pretty-printer queue at each call.
1770 If you need to print to some buffer b , you must first define a format‐
1772 ter writing to b , using let to_b = formatter_of_buffer b ; then use
1773 regular calls to Format.fprintf with formatter to_b .
1774 val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1778 Deprecated. An alias for ksprintf .
1780 val set_all_formatter_output_functions : out:(string -> int -> int ->
1784 unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int
1785 -> unit) -> unit
1786 Deprecated. Subsumed by set_formatter_out_functions .
1788 val get_all_formatter_output_functions : unit -> (string -> int -> int
1792 -> unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
1793 Deprecated. Subsumed by get_formatter_out_functions .
1795 val pp_set_all_formatter_output_functions : formatter -> out:(string ->
1799 int -> int -> unit) -> flush:(unit -> unit) -> newline:(unit -> unit)
1800 -> spaces:(int -> unit) -> unit
1801 Deprecated. Subsumed by pp_set_formatter_out_functions .
1803 val pp_get_all_formatter_output_functions : formatter -> unit ->
1807 (string -> int -> int -> unit) * (unit -> unit) * (unit -> unit) * (int
1808 -> unit)
1809 Deprecated. Subsumed by pp_get_formatter_out_functions .
1811 String tags
1816 val pp_open_tag : formatter -> tag -> unit
1817 Deprecated. Subsumed by Format.pp_open_stag .
1819 val open_tag : tag -> unit
1823 Deprecated. Subsumed by Format.open_stag .
1825 val pp_close_tag : formatter -> unit -> unit
1829 Deprecated. Subsumed by Format.pp_close_stag .
1831 val close_tag : unit -> unit
1835 Deprecated. Subsumed by Format.close_stag .
1837 type formatter_tag_functions = {
1840 mark_open_tag : tag -> string ;
1841 mark_close_tag : tag -> string ;
1842 print_open_tag : tag -> unit ;
1843 print_close_tag : tag -> unit ;
1844 }
1845 Deprecated. Subsumed by Format.formatter_stag_functions .
1848 val pp_set_formatter_tag_functions : formatter -> formatter_tag_func‐
1852 tions -> unit
1853 Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
1855 This function will erase non-string tag formatting functions.
1858 val set_formatter_tag_functions : formatter_tag_functions -> unit
1862 Deprecated. Subsumed by Format.set_formatter_stag_functions .
1864 val pp_get_formatter_tag_functions : formatter -> unit -> format‐
1868 ter_tag_functions
1869 Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
1871 val get_formatter_tag_functions : unit -> formatter_tag_functions
1875 Deprecated. Subsumed by Format.get_formatter_stag_functions .
1877OCamldoc 2020-09-01 Stdlib.Format(3)