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 (ac‐
394 cording 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. Us‐
439 ing 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 ef‐
486 ficiency.
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. Ei‐
566 ther decreasing the length of the parent box to make it fit on a line:
567 printf "@[123456@[7@]89@]@."
568 or opening an intermediary box before the maximum indentation limit
569 which fits on the current line
570 printf "@[123@[456@[7@]89@]A@]@."
571 avoids the rejection to the left of the inner boxes and print respec‐
572 tively "123456789" and "123456789A" . Note also that vertical boxes
573 never fit on a line whereas horizontal boxes always fully fit on the
574 current line. Opening a box may split a line whereas the contents may
575 have fit. If this behavior is problematic, it can be curtailed by set‐
576 ting the maximum indentation limit to margin - 1 . Note that setting
577 the maximum indentation limit to margin is invalid.
578 Nothing happens if d is smaller than 2.
580 If d is too large, the limit is set to the maximum admissible value
582 (which is greater than 10 ^ 9 ).
583 If d is greater or equal than the current margin, it is ignored, and
585 the current maximum indentation limit is kept.
586 See also Format.pp_set_geometry .
588 val pp_get_max_indent : formatter -> unit -> int
592 val get_max_indent : unit -> int
597 Return the maximum indentation limit (in characters).
599 Geometry
604 Geometric functions can be used to manipulate simultaneously the cou‐
605 pled variables, margin and maxixum indentation limit.
606 type geometry = {
608 max_indent : int ;
609 margin : int ;
610 }
611 val check_geometry : geometry -> bool
617 Check if the formatter geometry is valid: 1 < max_indent < margin
619 val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
624 val set_geometry : max_indent:int -> margin:int -> unit
629 val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int ->
634 unit
635 val safe_set_geometry : max_indent:int -> margin:int -> unit
640 pp_set_geometry ppf ~max_indent ~margin sets both the margin and maxi‐
643 mum indentation limit for ppf .
644 When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin
646 is equivalent to pp_set_margin ppf margin; pp_set_max_indent ppf
647 max_indent ; and avoids the subtly incorrect pp_set_max_indent ppf
648 max_indent; pp_set_margin ppf margin ;
649 Outside of this domain, pp_set_geometry raises an invalid argument ex‐
651 ception whereas pp_safe_set_geometry does nothing.
652 Since 4.08.0
655 val pp_update_geometry : formatter -> (geometry -> geometry) -> unit
659 pp_update_geometry ppf (fun geo -> { geo with ... }) lets you update a
662 formatter's geometry in a way that is robust to extension of the geome‐
663 try record with new fields.
664 Raises an invalid argument exception if the returned geometry does not
666 satisfy Format.check_geometry .
667 Since 4.11.0
670 val update_geometry : (geometry -> geometry) -> unit
674 val pp_get_geometry : formatter -> unit -> geometry
679 val get_geometry : unit -> geometry
684 Return the current geometry of the formatter
686 Since 4.08.0
689 Maximum formatting depth
694 The maximum formatting depth is the maximum number of pretty-printing
695 boxes simultaneously open.
696 Material inside boxes nested deeper is printed as an ellipsis (more
698 precisely as the text returned by Format.get_ellipsis_text () ).
699 val pp_set_max_boxes : formatter -> int -> unit
701 val set_max_boxes : int -> unit
706 pp_set_max_boxes ppf max sets the maximum number of pretty-printing
709 boxes simultaneously open.
710 Material inside boxes nested deeper is printed as an ellipsis (more
712 precisely as the text returned by Format.get_ellipsis_text () ).
713 Nothing happens if max is smaller than 2.
715 val pp_get_max_boxes : formatter -> unit -> int
719 val get_max_boxes : unit -> int
724 Returns the maximum number of pretty-printing boxes allowed before el‐
726 lipsis.
727 val pp_over_max_boxes : formatter -> unit -> bool
731 val over_max_boxes : unit -> bool
736 Tests if the maximum number of pretty-printing boxes allowed have al‐
738 ready been opened.
739 Tabulation boxes
744 A tabulation box prints material on lines divided into cells of fixed
745 length. A tabulation box provides a simple way to display vertical col‐
746 umns of left adjusted text.
747 This box features command set_tab to define cell boundaries, and com‐
749 mand print_tab to move from cell to cell and split the line when there
750 is no more cells to print on the line.
751 Note: printing within tabulation box is line directed, so arbitrary
753 line splitting inside a tabulation box leads to poor rendering. Yet,
754 controlled use of tabulation boxes allows simple printing of columns
755 within module Format .
756 val pp_open_tbox : formatter -> unit -> unit
758 val open_tbox : unit -> unit
763 open_tbox () opens a new tabulation box.
766 This box prints lines separated into cells of fixed width.
768 Inside a tabulation box, special tabulation markers defines points of
770 interest on the line (for instance to delimit cell boundaries). Func‐
771 tion Format.set_tab sets a tabulation marker at insertion point.
772 A tabulation box features specific tabulation breaks to move to next
774 tabulation marker or split the line. Function Format.print_tbreak
775 prints a tabulation break.
776 val pp_close_tbox : formatter -> unit -> unit
780 val close_tbox : unit -> unit
785 Closes the most recently opened tabulation box.
787 val pp_set_tab : formatter -> unit -> unit
791 val set_tab : unit -> unit
796 Sets a tabulation marker at current insertion point.
798 val pp_print_tab : formatter -> unit -> unit
802 val print_tab : unit -> unit
807 print_tab () emits a 'next' tabulation break hint: if not already set
810 on a tabulation marker, the insertion point moves to the first tabula‐
811 tion marker on the right, or the pretty-printer splits the line and in‐
812 sertion point moves to the leftmost tabulation marker.
813 It is equivalent to print_tbreak 0 0 .
815 val pp_print_tbreak : formatter -> int -> int -> unit
819 val print_tbreak : int -> int -> unit
824 print_tbreak nspaces offset emits a 'full' tabulation break hint.
827 If not already set on a tabulation marker, the insertion point moves to
829 the first tabulation marker on the right and the pretty-printer prints
830 nspaces spaces.
831 If there is no next tabulation marker on the right, the pretty-printer
833 splits the line at this point, then insertion point moves to the left‐
834 most tabulation marker of the box.
835 If the pretty-printer splits the line, offset is added to the current
837 indentation.
838 Ellipsis
843 val pp_set_ellipsis_text : formatter -> string -> unit
844 val set_ellipsis_text : string -> unit
849 Set the text of the ellipsis printed when too many pretty-printing
851 boxes are open (a single dot, . , by default).
852 val pp_get_ellipsis_text : formatter -> unit -> string
856 val get_ellipsis_text : unit -> string
861 Return the text of the ellipsis.
863 Semantic tags
868 type stag = ..
869 Semantic tags (or simply tags) are user's defined annotations to asso‐
872 ciate user's specific operations to printed entities.
873 Common usage of semantic tags is text decoration to get specific font
875 or text size rendering for a display device, or marking delimitation of
876 entities (e.g. HTML or TeX elements or terminal escape sequences).
877 More sophisticated usage of semantic tags could handle dynamic modifi‐
878 cation of the pretty-printer behavior to properly print the material
879 within some specific tags. For instance, we can define an RGB tag like
880 so:
881 type stag += RGB of {r:int;g:int;b:int}
882 In order to properly delimit printed entities, a semantic tag must be
885 opened before and closed after the entity. Semantic tags must be prop‐
886 erly nested like parentheses using Format.pp_open_stag and For‐
887 mat.pp_close_stag .
888 Tag specific operations occur any time a tag is opened or closed, At
890 each occurrence, two kinds of operations are performed tag-marking and
891 tag-printing:
892 -The tag-marking operation is the simpler tag specific operation: it
894 simply writes a tag specific string into the output device of the for‐
895 matter. Tag-marking does not interfere with line-splitting computation.
896 -The tag-printing operation is the more involved tag specific opera‐
898 tion: it can print arbitrary material to the formatter. Tag-printing is
899 tightly linked to the current pretty-printer operations.
900 Roughly speaking, tag-marking is commonly used to get a better render‐
902 ing of texts in the rendering device, while tag-printing allows fine
903 tuning of printing routines to print the same entity differently ac‐
904 cording to the semantic tags (i.e. print additional material or even
905 omit parts of the output).
906 More precisely: when a semantic tag is opened or closed then both and
908 successive 'tag-printing' and 'tag-marking' operations occur:
909 -Tag-printing a semantic tag means calling the formatter specific func‐
911 tion print_open_stag (resp. print_close_stag ) with the name of the
912 tag as argument: that tag-printing function can then print any regular
913 material to the formatter (so that this material is enqueued as usual
914 in the formatter queue for further line splitting computation).
915 -Tag-marking a semantic tag means calling the formatter specific func‐
917 tion mark_open_stag (resp. mark_close_stag ) with the name of the tag
918 as argument: that tag-marking function can then return the 'tag-opening
919 marker' (resp. `tag-closing marker') for direct output into the output
920 device of the formatter.
921 Being written directly into the output device of the formatter, seman‐
923 tic tag marker strings are not considered as part of the printing mate‐
924 rial that drives line splitting (in other words, the length of the
925 strings corresponding to tag markers is considered as zero for line
926 splitting).
927 Thus, semantic tag handling is in some sense transparent to
929 pretty-printing and does not interfere with usual indentation. Hence, a
930 single pretty-printing routine can output both simple 'verbatim' mate‐
931 rial or richer decorated output depending on the treatment of tags. By
932 default, tags are not active, hence the output is not decorated with
933 tag information. Once set_tags is set to true , the pretty-printer en‐
934 gine honors tags and decorates the output accordingly.
935 Default tag-marking functions behave the HTML way: Format.tag are en‐
937 closed in "<" and ">" while other tags are ignored; hence, opening
938 marker for tag string "t" is "<t>" and closing marker is "</t>" .
939 Default tag-printing functions just do nothing.
941 Tag-marking and tag-printing functions are user definable and can be
943 set by calling Format.set_formatter_stag_functions .
944 Semantic tag operations may be set on or off with Format.set_tags .
946 Tag-marking operations may be set on or off with Format.set_mark_tags .
947 Tag-printing operations may be set on or off with Format.set_print_tags
948 .
949 type tag = string
952 type Format.stag +=
957 | String_tag of tag (* String_tag s is a string tag s . String tags
958 can be inserted either by explicitly using the constructor String_tag
959 or by using the dedicated format syntax "@{<s> ... @}" .
960 *)
961 val pp_open_stag : formatter -> stag -> unit
967 val open_stag : stag -> unit
972 pp_open_stag ppf t opens the semantic tag named t .
975 The print_open_stag tag-printing function of the formatter is called
977 with t as argument; then the opening tag marker for t , as given by
978 mark_open_stag t , is written into the output device of the formatter.
979 val pp_close_stag : formatter -> unit -> unit
983 val close_stag : unit -> unit
988 pp_close_stag ppf () closes the most recently opened semantic tag t .
991 The closing tag marker, as given by mark_close_stag t , is written into
993 the output device of the formatter; then the print_close_stag
994 tag-printing function of the formatter is called with t as argument.
995 val pp_set_tags : formatter -> bool -> unit
999 val set_tags : bool -> unit
1004 pp_set_tags ppf b turns on or off the treatment of semantic tags (de‐
1007 fault is off).
1008 val pp_set_print_tags : formatter -> bool -> unit
1012 val set_print_tags : bool -> unit
1017 pp_set_print_tags ppf b turns on or off the tag-printing operations.
1020 val pp_set_mark_tags : formatter -> bool -> unit
1024 val set_mark_tags : bool -> unit
1029 pp_set_mark_tags ppf b turns on or off the tag-marking operations.
1032 val pp_get_print_tags : formatter -> unit -> bool
1036 val get_print_tags : unit -> bool
1041 Return the current status of tag-printing operations.
1043 val pp_get_mark_tags : formatter -> unit -> bool
1047 val get_mark_tags : unit -> bool
1052 Return the current status of tag-marking operations.
1054 val pp_set_formatter_out_channel : formatter -> out_channel -> unit
1058 Redirecting the standard formatter output
1061 val set_formatter_out_channel : out_channel -> unit
1062 Redirect the standard pretty-printer output to the given channel. (All
1064 the output functions of the standard formatter are set to the default
1065 output functions printing to the given channel.)
1066 set_formatter_out_channel is equivalent to Format.pp_set_format‐
1069 ter_out_channel std_formatter .
1070 val pp_set_formatter_output_functions : formatter -> (string -> int ->
1074 int -> unit) -> (unit -> unit) -> unit
1075 val set_formatter_output_functions : (string -> int -> int -> unit) ->
1080 (unit -> unit) -> unit
1081 pp_set_formatter_output_functions ppf out flush redirects the standard
1084 pretty-printer output functions to the functions out and flush .
1085 The out function performs all the pretty-printer string output. It is
1087 called with a string s , a start position p , and a number of charac‐
1088 ters n ; it is supposed to output characters p to p + n - 1 of s .
1089 The flush function is called whenever the pretty-printer is flushed
1091 (via conversion %! , or pretty-printing indications @? or @. , or
1092 using low level functions print_flush or print_newline ).
1093 val pp_get_formatter_output_functions : formatter -> unit -> (string ->
1097 int -> int -> unit) * (unit -> unit)
1098 val get_formatter_output_functions : unit -> (string -> int -> int ->
1103 unit) * (unit -> unit)
1104 Return the current output functions of the standard pretty-printer.
1106 Redefining formatter output
1111 The Format module is versatile enough to let you completely redefine
1112 the meaning of pretty-printing output: you may provide your own func‐
1113 tions to define how to handle indentation, line splitting, and even
1114 printing of all the characters that have to be printed!
1115 Redefining output functions
1117 type formatter_out_functions = {
1118 out_string : string -> int -> int -> unit ;
1119 out_flush : unit -> unit ;
1120 out_newline : unit -> unit ;
1121 out_spaces : int -> unit ;
1122 out_indent : int -> unit ;
1123 }
1124 The set of output functions specific to a formatter:
1127 -the out_string function performs all the pretty-printer string output.
1129 It is called with a string s , a start position p , and a number of
1130 characters n ; it is supposed to output characters p to p + n - 1 of s
1131 .
1132 -the out_flush function flushes the pretty-printer output device.
1134 - out_newline is called to open a new line when the pretty-printer
1136 splits the line.
1137 -the out_spaces function outputs spaces when a break hint leads to spa‐
1139 ces instead of a line split. It is called with the number of spaces to
1140 output.
1141 -the out_indent function performs new line indentation when the
1143 pretty-printer splits the line. It is called with the indentation value
1144 of the new line.
1145 By default:
1147 -fields out_string and out_flush are output device specific; (e.g.
1149 output_string and flush for a out_channel device, or Buffer.add_sub‐
1150 string and ignore for a Buffer.t output device),
1151 -field out_newline is equivalent to out_string "\n" 0 1 ;
1153 -fields out_spaces and out_indent are equivalent to out_string
1155 (String.make n ' ') 0 n .
1156 Since 4.01.0
1160 val pp_set_formatter_out_functions : formatter -> formatter_out_func‐
1164 tions -> unit
1165 val set_formatter_out_functions : formatter_out_functions -> unit
1170 pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer
1173 output functions of ppf to those of argument out_funs ,
1174 This way, you can change the meaning of indentation (which can be some‐
1176 thing else than just printing space characters) and the meaning of new
1177 lines opening (which can be connected to any other action needed by the
1178 application at hand).
1179 Reasonable defaults for functions out_spaces and out_newline are re‐
1181 spectively out_funs.out_string (String.make n ' ') 0 n and
1182 out_funs.out_string "\n" 0 1 .
1183 Since 4.01.0
1186 val pp_get_formatter_out_functions : formatter -> unit -> format‐
1190 ter_out_functions
1191 val get_formatter_out_functions : unit -> formatter_out_functions
1196 Return the current output functions of the pretty-printer, including
1198 line splitting and indentation functions. Useful to record the current
1199 setting and restore it afterwards.
1200 Since 4.01.0
1203 Redefining semantic tag operations
1208 type formatter_stag_functions = {
1209 mark_open_stag : stag -> string ;
1210 mark_close_stag : stag -> string ;
1211 print_open_stag : stag -> unit ;
1212 print_close_stag : stag -> unit ;
1213 }
1214 The semantic tag handling functions specific to a formatter: mark ver‐
1217 sions are the 'tag-marking' functions that associate a string marker to
1218 a tag in order for the pretty-printing engine to write those markers as
1219 0 length tokens in the output device of the formatter. print versions
1220 are the 'tag-printing' functions that can perform regular printing when
1221 a tag is closed or opened.
1222 val pp_set_formatter_stag_functions : formatter -> formatter_stag_func‐
1226 tions -> unit
1227 val set_formatter_stag_functions : formatter_stag_functions -> unit
1232 pp_set_formatter_stag_functions ppf tag_funs changes the meaning of
1235 opening and closing semantic tag operations to use the functions in
1236 tag_funs when printing on ppf .
1237 When opening a semantic tag with name t , the string t is passed to the
1239 opening tag-marking function (the mark_open_stag field of the record
1240 tag_funs ), that must return the opening tag marker for that name. When
1241 the next call to close_stag () happens, the semantic tag name t is sent
1242 back to the closing tag-marking function (the mark_close_stag field of
1243 record tag_funs ), that must return a closing tag marker for that name.
1244 The print_ field of the record contains the tag-printing functions that
1246 are called at tag opening and tag closing time, to output regular mate‐
1247 rial in the pretty-printer queue.
1248 val pp_get_formatter_stag_functions : formatter -> unit -> format‐
1252 ter_stag_functions
1253 val get_formatter_stag_functions : unit -> formatter_stag_functions
1258 Return the current semantic tag operation functions of the standard
1260 pretty-printer.
1261 Defining formatters
1266 Defining new formatters permits unrelated output of material in paral‐
1267 lel on several output devices. All the parameters of a formatter are
1268 local to the formatter: right margin, maximum indentation limit, maxi‐
1269 mum number of pretty-printing boxes simultaneously open, ellipsis, and
1270 so on, are specific to each formatter and may be fixed independently.
1271 For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b
1273 returns a new formatter using buffer b as its output device. Simi‐
1274 larly, given a out_channel output channel oc , Format.format‐
1275 ter_of_out_channel oc returns a new formatter using channel oc as its
1276 output device.
1277 Alternatively, given out_funs , a complete set of output functions for
1279 a formatter, then Format.formatter_of_out_functions out_funs computes a
1280 new formatter using those functions for output.
1281 val formatter_of_out_channel : out_channel -> formatter
1283 formatter_of_out_channel oc returns a new formatter writing to the cor‐
1286 responding output channel oc .
1287 val std_formatter : formatter
1291 The standard formatter to write to standard output.
1293 It is defined as Format.formatter_of_out_channel stdout .
1295 val err_formatter : formatter
1299 A formatter to write to standard error.
1301 It is defined as Format.formatter_of_out_channel stderr .
1303 val formatter_of_buffer : Buffer.t -> formatter
1307 formatter_of_buffer b returns a new formatter writing to buffer b . At
1310 the end of pretty-printing, the formatter must be flushed using For‐
1311 mat.pp_print_flush or Format.pp_print_newline , to print all the pend‐
1312 ing material into the buffer.
1313 val stdbuf : Buffer.t
1317 The string buffer in which str_formatter writes.
1319 val str_formatter : formatter
1323 A formatter to output to the Format.stdbuf string buffer.
1325 str_formatter is defined as Format.formatter_of_buffer Format.stdbuf .
1328 val flush_str_formatter : unit -> string
1332 Returns the material printed with str_formatter , flushes the formatter
1334 and resets the corresponding buffer.
1335 val make_formatter : (string -> int -> int -> unit) -> (unit -> unit)
1339 -> formatter
1340 make_formatter out flush returns a new formatter that outputs with
1343 function out , and flushes with function flush .
1344 For instance,
1346 make_formatter
1347 (Stdlib.output oc)
1348 (fun () -> Stdlib.flush oc)
1349 returns a formatter to the out_channel oc .
1350 val formatter_of_out_functions : formatter_out_functions -> formatter
1354 formatter_of_out_functions out_funs returns a new formatter that writes
1357 with the set of output functions out_funs .
1358 See definition of type Format.formatter_out_functions for the meaning
1360 of argument out_funs .
1361 Since 4.06.0
1364 Symbolic pretty-printing
1369 Symbolic pretty-printing is pretty-printing using a symbolic formatter,
1370 i.e. a formatter that outputs symbolic pretty-printing items.
1371 When using a symbolic formatter, all regular pretty-printing activities
1373 occur but output material is symbolic and stored in a buffer of output
1374 items. At the end of pretty-printing, flushing the output buffer al‐
1375 lows post-processing of symbolic output before performing low level
1376 output operations.
1377 In practice, first define a symbolic output buffer b using:
1379 - let sob = make_symbolic_output_buffer () . Then define a symbolic
1381 formatter with:
1382 - let ppf = formatter_of_symbolic_output_buffer sob
1384 Use symbolic formatter ppf as usual, and retrieve symbolic items at end
1386 of pretty-printing by flushing symbolic output buffer sob with:
1387 - flush_symbolic_output_buffer sob .
1389 type symbolic_output_item =
1392 | Output_flush (* symbolic flush command
1393 *)
1394 | Output_newline (* symbolic newline command
1395 *)
1396 | Output_string of string
1397 (* Output_string s : symbolic output for string s
1398 *)
1400 | Output_spaces of int
1401 (* Output_spaces n : symbolic command to output n spaces
1402 *)
1403 | Output_indent of int
1404 (* Output_indent i : symbolic indentation of size i
1405 *)
1407 Items produced by symbolic pretty-printers
1410 Since 4.06.0
1413 type symbolic_output_buffer
1416 The output buffer of a symbolic pretty-printer.
1419 Since 4.06.0
1422 val make_symbolic_output_buffer : unit -> symbolic_output_buffer
1426 make_symbolic_output_buffer () returns a fresh buffer for symbolic out‐
1429 put.
1430 Since 4.06.0
1433 val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
1437 clear_symbolic_output_buffer sob resets buffer sob .
1440 Since 4.06.0
1443 val get_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1447 bolic_output_item list
1448 get_symbolic_output_buffer sob returns the contents of buffer sob .
1451 Since 4.06.0
1454 val flush_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1458 bolic_output_item list
1459 flush_symbolic_output_buffer sob returns the contents of buffer sob and
1462 resets buffer sob . flush_symbolic_output_buffer sob is equivalent to
1463 let items = get_symbolic_output_buffer sob in
1464 clear_symbolic_output_buffer sob; items
1465 Since 4.06.0
1469 val add_symbolic_output_item : symbolic_output_buffer -> symbolic_out‐
1473 put_item -> unit
1474 add_symbolic_output_item sob itm adds item itm to buffer sob .
1477 Since 4.06.0
1480 val formatter_of_symbolic_output_buffer : symbolic_output_buffer ->
1484 formatter
1485 formatter_of_symbolic_output_buffer sob returns a symbolic formatter
1488 that outputs to symbolic_output_buffer sob .
1489 Since 4.06.0
1492 Convenience formatting functions.
1497 val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter
1498 -> 'a -> unit) -> formatter -> 'a list -> unit
1499 pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to
1502 print each item, and calling pp_sep between items ( pp_sep defaults to
1503 Format.pp_print_cut . Does nothing on empty lists.
1504 Since 4.02.0
1507 val pp_print_text : formatter -> string -> unit
1511 pp_print_text ppf s prints s with spaces and newlines respectively
1514 printed using Format.pp_print_space and Format.pp_force_newline .
1515 Since 4.02.0
1518 val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter
1522 -> 'a -> unit) -> formatter -> 'a option -> unit
1523 pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is
1526 Some v and none if it is None . none prints nothing by default.
1527 Since 4.08
1530 val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter
1534 -> 'e -> unit) -> formatter -> ('a, 'e) result -> unit
1535 pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _
1538 and error if r is Error _ .
1539 Since 4.08
1542 Formatted pretty-printing
1547 Module Format provides a complete set of printf like functions for
1548 pretty-printing using format string specifications.
1549 Specific annotations may be added in the format strings to give
1551 pretty-printing commands to the pretty-printing engine.
1552 Those annotations are introduced in the format strings using the @
1554 character. For instance, @ means a space break, @, means a cut, @[
1555 opens a new box, and @] closes the last open box.
1556 val fprintf : formatter -> ('a, formatter, unit) format -> 'a
1558 fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN accord‐
1564 ing to the format string fmt , and outputs the resulting string on the
1565 formatter ff .
1566 The format string fmt is a character string which contains three types
1568 of objects: plain characters and conversion specifications as specified
1569 in the Printf module, and pretty-printing indications specific to the
1570 Format module.
1571 The pretty-printing indication characters are introduced by a @ charac‐
1573 ter, and their meanings are:
1574 - @[ : open a pretty-printing box. The type and offset of the box may
1576 be optionally specified with the following syntax: the < character,
1577 followed by an optional box type indication, then an optional integer
1578 offset, and the closing > character. Pretty-printing box type is one
1579 of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
1580 pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box,
1581 ' hv ' stands for an 'horizontal/vertical' pretty-printing box, ' b '
1582 stands for an 'horizontal-or-vertical' pretty-printing box demonstrat‐
1583 ing indentation, ' hov ' stands a simple 'horizontal-or-vertical'
1584 pretty-printing box. For instance, @[<hov 2> opens an 'horizon‐
1585 tal-or-vertical' pretty-printing box with indentation 2 as obtained
1586 with open_hovbox 2 . For more details about pretty-printing boxes, see
1587 the various box opening functions open_*box .
1588 - @] : close the most recently opened pretty-printing box.
1590 - @, : output a 'cut' break hint, as with print_cut () .
1592 - @ : output a 'space' break hint, as with print_space () .
1594 - @; : output a 'full' break hint as with print_break . The nspaces and
1596 offset parameters of the break hint may be optionally specified with
1597 the following syntax: the < character, followed by an integer nspaces
1598 value, then an integer offset , and a closing > character. If no pa‐
1599 rameters are provided, the good break defaults to a 'space' break hint.
1600 - @. : flush the pretty-printer and split the line, as with print_new‐
1602 line () .
1603 - @<n> : print the following item as if it were of length n . Hence,
1605 printf "@<0>%s" arg prints arg as a zero length string. If @<n> is not
1606 followed by a conversion specification, then the following character of
1607 the format is printed as if it were of length n .
1608 - @{ : open a semantic tag. The name of the tag may be optionally spec‐
1610 ified with the following syntax: the < character, followed by an op‐
1611 tional string specification, and the closing > character. The string
1612 specification is any character string that does not contain the closing
1613 character '>' . If omitted, the tag name defaults to the empty string.
1614 For more details about semantic tags, see the functions For‐
1615 mat.open_stag and Format.close_stag .
1616 - @} : close the most recently opened semantic tag.
1618 - @? : flush the pretty-printer as with print_flush () . This is
1620 equivalent to the conversion %! .
1621 - @\n : force a newline, as with force_newline () , not the normal way
1623 of pretty-printing, you should prefer using break hints inside a verti‐
1624 cal pretty-printing box.
1625 Note: To prevent the interpretation of a @ character as a pretty-print‐
1627 ing indication, escape it with a % character. Old quotation mode @@ is
1628 deprecated since it is not compatible with formatted input interpreta‐
1629 tion of character '@' .
1630 Example: printf "@[%s@ %d@]@." "x =" 1 is equivalent to open_box ();
1632 print_string "x ="; print_space ();
1633 print_int 1; close_box (); print_newline () . It prints x = 1
1634 within a pretty-printing 'horizontal-or-vertical' box.
1635 val printf : ('a, formatter, unit) format -> 'a
1637 Same as fprintf above, but output on std_formatter .
1639 val eprintf : ('a, formatter, unit) format -> 'a
1643 Same as fprintf above, but output on err_formatter .
1645 val sprintf : ('a, unit, string) format -> 'a
1649 Same as printf above, but instead of printing on a formatter, returns a
1651 string containing the result of formatting the arguments. Note that
1652 the pretty-printer queue is flushed at the end of each call to sprintf
1653 .
1654 In case of multiple and related calls to sprintf to output material on
1656 a single string, you should consider using fprintf with the predefined
1657 formatter str_formatter and call flush_str_formatter () to get the fi‐
1658 nal result.
1659 Alternatively, you can use Format.fprintf with a formatter writing to a
1661 buffer of your own: flushing the formatter and the buffer at the end of
1662 pretty-printing returns the desired string.
1663 val asprintf : ('a, formatter, unit, string) format4 -> 'a
1667 Same as printf above, but instead of printing on a formatter, returns a
1669 string containing the result of formatting the arguments. The type of
1670 asprintf is general enough to interact nicely with %a conversions.
1671 Since 4.01.0
1674 val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
1678 Same as Format.fprintf , except the formatter is the last argument.
1680 dprintf "..." a b c is a function of type formatter -> unit which can
1681 be given to a format specifier %t .
1682 This can be used as a replacement for Format.asprintf to delay format‐
1684 ting decisions. Using the string returned by Format.asprintf in a for‐
1685 matting context forces formatting decisions to be taken in isolation,
1686 and the final string may be created prematurely. Format.dprintf allows
1687 delay of formatting decisions until the final formatting context is
1688 known. For example:
1689 let t = Format.dprintf "%i@ %i@ %i" 1 2 3 in
1690 ...
1691 Format.printf "@[<v>%t@]" t
1692 Since 4.08.0
1696 val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
1700 Same as fprintf above, but does not print anything. Useful to ignore
1702 some material when conditionally printing.
1703 Since 3.10.0
1706 Formatted Pretty-Printing with continuations.
1711 val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1713 'a) format4 -> 'b
1714 Same as fprintf above, but instead of returning immediately, passes the
1716 formatter to its first argument at the end of printing.
1717 val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a)
1721 format4 -> 'b
1722 Same as Format.dprintf above, but instead of returning immediately,
1724 passes the suspended printer to its first argument at the end of print‐
1725 ing.
1726 Since 4.08.0
1729 val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1733 'a) format4 -> 'b
1734 Same as kfprintf above, but does not print anything. Useful to ignore
1736 some material when conditionally printing.
1737 Since 3.12.0
1740 val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1744 Same as sprintf above, but instead of returning the string, passes it
1746 to the first argument.
1747 val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 ->
1751 'b
1752 Same as asprintf above, but instead of returning the string, passes it
1754 to the first argument.
1755 Since 4.03
1758 Deprecated
1763 val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
1764 Deprecated. This function is error prone. Do not use it. This func‐
1766 tion is neither compositional nor incremental, since it flushes the
1767 pretty-printer queue at each call.
1768 If you need to print to some buffer b , you must first define a format‐
1770 ter writing to b , using let to_b = formatter_of_buffer b ; then use
1771 regular calls to Format.fprintf with formatter to_b .
1772 val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1776 Deprecated. An alias for ksprintf .
1778 val set_all_formatter_output_functions : out:(string -> int -> int ->
1782 unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int
1783 -> unit) -> unit
1784 Deprecated. Subsumed by set_formatter_out_functions .
1786 val get_all_formatter_output_functions : unit -> (string -> int -> int
1790 -> unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
1791 Deprecated. Subsumed by get_formatter_out_functions .
1793 val pp_set_all_formatter_output_functions : formatter -> out:(string ->
1797 int -> int -> unit) -> flush:(unit -> unit) -> newline:(unit -> unit)
1798 -> spaces:(int -> unit) -> unit
1799 Deprecated. Subsumed by pp_set_formatter_out_functions .
1801 val pp_get_all_formatter_output_functions : formatter -> unit ->
1805 (string -> int -> int -> unit) * (unit -> unit) * (unit -> unit) * (int
1806 -> unit)
1807 Deprecated. Subsumed by pp_get_formatter_out_functions .
1809 String tags
1814 val pp_open_tag : formatter -> tag -> unit
1815 Deprecated. Subsumed by Format.pp_open_stag .
1817 val open_tag : tag -> unit
1821 Deprecated. Subsumed by Format.open_stag .
1823 val pp_close_tag : formatter -> unit -> unit
1827 Deprecated. Subsumed by Format.pp_close_stag .
1829 val close_tag : unit -> unit
1833 Deprecated. Subsumed by Format.close_stag .
1835 type formatter_tag_functions = {
1838 mark_open_tag : tag -> string ;
1839 mark_close_tag : tag -> string ;
1840 print_open_tag : tag -> unit ;
1841 print_close_tag : tag -> unit ;
1842 }
1843 Deprecated. Subsumed by Format.formatter_stag_functions .
1846 val pp_set_formatter_tag_functions : formatter -> formatter_tag_func‐
1850 tions -> unit
1851 Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
1853 This function will erase non-string tag formatting functions.
1856 val set_formatter_tag_functions : formatter_tag_functions -> unit
1860 Deprecated. Subsumed by Format.set_formatter_stag_functions .
1862 val pp_get_formatter_tag_functions : formatter -> unit -> format‐
1866 ter_tag_functions
1867 Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
1869 val get_formatter_tag_functions : unit -> formatter_tag_functions
1873 Deprecated. Subsumed by Format.get_formatter_stag_functions .
1875OCamldoc 2021-01-26 Stdlib.Format(3)