1Format(3) OCaml library Format(3)
2
6 Format - Pretty-printing.
7
9 Module Format
10
12 Module Format
13 : sig end
14 Pretty-printing.
17 This module implements a pretty-printing facility to format values
19 within Format.boxes and Format.tags combined with a set of Format.fpp .
20 The pretty-printer splits lines at specified Format.breaks , and
21 indents lines according to the box structure. Similarly, Format.tags
22 can be used to decouple text presentation from its contents.
23 This pretty-printing facility is implemented as an overlay on top of
25 abstract Format.formatter which provide basic output functions. Some
26 formatters are predefined, notably:
27 - Format.std_formatter outputs to stdout
29 - Format.err_formatter outputs to stderr
32 Most functions in the Format module come in two variants: a short ver‐
34 sion that operates on Format.std_formatter and the generic version pre‐
35 fixed by pp_ that takes a formatter as its first argument.
36 More formatters can be created with Format.formatter_of_out_channel ,
38 Format.formatter_of_buffer , Format.formatter_of_symbolic_output_buffer
39 or using Format.formatter .
40 Introduction
48 For a gentle introduction to the basics of pretty-printing using Format
49 , read http://caml.inria.fr/resources/doc/guides/format.en.html.
50 You may consider this module as providing an extension to the printf
52 facility to provide automatic line splitting. The addition of
53 pretty-printing annotations to your regular printf format strings gives
54 you fancy indentation and line breaks. Pretty-printing annotations are
55 described below in the documentation of the function Format.fprintf .
56 You may also use the explicit pretty-printing box management and print‐
58 ing functions provided by this module. This style is more basic but
59 more verbose than the concise fprintf format strings.
60 For instance, the sequence open_box 0; print_string "x ="; print_space
62 ();
63 print_int 1; close_box (); print_newline () that prints x = 1
64 within a pretty-printing box, can be abbreviated as printf "@[%s@
65 %i@]@." "x =" 1 , or even shorter printf "@[x =@ %i@]@." 1 .
66 Rule of thumb for casual users of this library:
68 -use simple pretty-printing boxes (as obtained by open_box 0 );
70 -use simple break hints as obtained by print_cut () that outputs a sim‐
72 ple break hint, or by print_space () that outputs a space indicating a
73 break hint;
74 -once a pretty-printing box is open, display its material with basic
76 printing functions (e. g. print_int and print_string );
77 -when the material for a pretty-printing box has been printed, call
79 close_box () to close the box;
80 -at the end of pretty-printing, flush the pretty-printer to display all
82 the remaining material, e.g. evaluate print_newline () .
83 The behavior of pretty-printing commands is unspecified if there is no
85 open pretty-printing box. Each box opened by one of the open_ functions
86 below must be closed using close_box for proper formatting. Otherwise,
87 some of the material printed in the boxes may not be output, or may be
88 formatted incorrectly.
89 In case of interactive use, each phrase is executed in the initial
91 state of the standard pretty-printer: after each phrase execution, the
92 interactive system closes all open pretty-printing boxes, flushes all
93 pending text, and resets the standard pretty-printer.
94 Warning: mixing calls to pretty-printing functions of this module with
96 calls to Stdlib low level output functions is error prone.
97 The pretty-printing functions output material that is delayed in the
99 pretty-printer queue and stacks in order to compute proper line split‐
100 ting. In contrast, basic I/O output functions write directly in their
101 output device. As a consequence, the output of a basic I/O function may
102 appear before the output of a pretty-printing function that has been
103 called before. For instance,
104 Stdlib.print_string "<";
105 Format.print_string "PRETTY";
106 Stdlib.print_string ">";
107 Format.print_string "TEXT";
108 leads to output <>PRETTYTEXT .
109 type formatter
111 Abstract data corresponding to a pretty-printer (also called a format‐
114 ter) and all its machinery. See also Format.formatter .
115 Pretty-printing boxes
120 The pretty-printing engine uses the concepts of pretty-printing box and
121 break hint to drive indentation and line splitting behavior of the
122 pretty-printer.
123 Each different pretty-printing box kind introduces a specific line
125 splitting policy:
126 -within an horizontal box, break hints never split the line (but the
129 line may be split in a box nested deeper),
130 -within a vertical box, break hints always split the line,
132 -within an horizontal/vertical box, if the box fits on the current line
134 then break hints never split the line, otherwise break hint always
135 split the line,
136 -within a compacting box, a break hint never splits the line, unless
138 there is no more room on the current line.
139 Note that line splitting policy is box specific: the policy of a box
141 does not rule the policy of inner boxes. For instance, if a vertical
142 box is nested in an horizontal box, all break hints within the vertical
143 box will split the line.
144 val pp_open_box : formatter -> int -> unit
146 val open_box : int -> unit
151 pp_open_box ppf d opens a new compacting pretty-printing box with off‐
154 set d in the formatter ppf .
155 Within this box, the pretty-printer prints as much as possible material
157 on every line.
158 A break hint splits the line if there is no more room on the line to
160 print the remainder of the box.
161 Within this box, the pretty-printer emphasizes the box structure: a
163 break hint also splits the line if the splitting ``moves to the left''
164 (i.e. the new line gets an indentation smaller than the one of the cur‐
165 rent line).
166 This box is the general purpose pretty-printing box.
168 If the pretty-printer splits the line in the box, offset d is added to
170 the current indentation.
171 val pp_close_box : formatter -> unit -> unit
175 val close_box : unit -> unit
180 Closes the most recently open pretty-printing box.
182 val pp_open_hbox : formatter -> unit -> unit
186 val open_hbox : unit -> unit
191 pp_open_hbox ppf () opens a new 'horizontal' pretty-printing box.
194 This box prints material on a single line.
196 Break hints in a horizontal box never split the line. (Line splitting
198 may still occur inside boxes nested deeper).
199 val pp_open_vbox : formatter -> int -> unit
203 val open_vbox : int -> unit
208 pp_open_vbox ppf d opens a new 'vertical' pretty-printing box with off‐
211 set d .
212 This box prints material on as many lines as break hints in the box.
214 Every break hint in a vertical box splits the line.
216 If the pretty-printer splits the line in the box, d is added to the
218 current indentation.
219 val pp_open_hvbox : formatter -> int -> unit
223 val open_hvbox : int -> unit
228 pp_open_hvbox ppf d opens a new 'horizontal/vertical' pretty-printing
231 box with offset d .
232 This box behaves as an horizontal box if it fits on a single line, oth‐
234 erwise it behaves as a vertical box.
235 If the pretty-printer splits the line in the box, d is added to the
237 current indentation.
238 val pp_open_hovbox : formatter -> int -> unit
242 val open_hovbox : int -> unit
247 pp_open_hovbox ppf d opens a new 'horizontal-or-vertical' pretty-print‐
250 ing box with offset d .
251 This box prints material as much as possible on every line.
253 A break hint splits the line if there is no more room on the line to
255 print the remainder of the box.
256 If the pretty-printer splits the line in the box, d is added to the
258 current indentation.
259 Formatting functions
264 val pp_print_string : formatter -> string -> unit
265 val print_string : string -> unit
270 pp_print_string ppf s prints s in the current pretty-printing box.
273 val pp_print_as : formatter -> int -> string -> unit
277 val print_as : int -> string -> unit
282 pp_print_as ppf len s prints s in the current pretty-printing box. The
285 pretty-printer formats s as if it were of length len .
286 val pp_print_int : formatter -> int -> unit
290 val print_int : int -> unit
295 Print an integer in the current pretty-printing box.
297 val pp_print_float : formatter -> float -> unit
301 val print_float : float -> unit
306 Print a floating point number in the current pretty-printing box.
308 val pp_print_char : formatter -> char -> unit
312 val print_char : char -> unit
317 Print a character in the current pretty-printing box.
319 val pp_print_bool : formatter -> bool -> unit
323 val print_bool : bool -> unit
328 Print a boolean in the current pretty-printing box.
330 Break hints
335 A 'break hint' tells the pretty-printer to output some space or split
336 the line whichever way is more appropriate to the current pretty-print‐
337 ing box splitting rules.
338 Break hints are used to separate printing items and are mandatory to
340 let the pretty-printer correctly split lines and indent items.
341 Simple break hints are:
343 -the 'space': output a space or split the line if appropriate,
345 -the 'cut': split the line if appropriate.
347 Note: the notions of space and line splitting are abstract for the
349 pretty-printing engine, since those notions can be completely redefined
350 by the programmer. However, in the pretty-printer default setting,
351 ``output a space'' simply means printing a space character (ASCII code
352 32) and ``split the line'' means printing a newline character (ASCII
353 code 10).
354 val pp_print_space : formatter -> unit -> unit
356 val print_space : unit -> unit
361 pp_print_space ppf () emits a 'space' break hint: the pretty-printer
364 may split the line at this point, otherwise it prints one space.
365 pp_print_space ppf () is equivalent to pp_print_break ppf 1 0 .
368 val pp_print_cut : formatter -> unit -> unit
372 val print_cut : unit -> unit
377 pp_print_cut ppf () emits a 'cut' break hint: the pretty-printer may
380 split the line at this point, otherwise it prints nothing.
381 pp_print_cut ppf () is equivalent to pp_print_break ppf 0 0 .
384 val pp_print_break : formatter -> int -> int -> unit
388 val print_break : int -> int -> unit
393 pp_print_break ppf nspaces offset emits a 'full' break hint: the
396 pretty-printer may split the line at this point, otherwise it prints
397 nspaces spaces.
398 If the pretty-printer splits the line, offset is added to the current
400 indentation.
401 val pp_print_custom_break : formatter -> fits:string * int * string ->
405 breaks:string * int * string -> unit
406 pp_print_custom_break ppf ~fits:(s1, n, s2) ~breaks:(s3, m, s4) emits a
409 custom break hint: the pretty-printer may split the line at this point.
410 If it does not split the line, then the s1 is emitted, then n spaces,
412 then s2 .
413 If it splits the line, then it emits the s3 string, then an indent
415 (according to the box rules), then an offset of m spaces, then the s4
416 string.
417 While n and m are handled by formatter_out_functions.out_indent , the
419 strings will be handled by formatter_out_functions.out_string . This
420 allows for a custom formatter that handles indentation distinctly, for
421 example, outputs <br/> tags or entities.
422 The custom break is useful if you want to change which visible
424 (non-whitespace) characters are printed in case of break or no break.
425 For example, when printing a list
426 [a; b; c]
427 trailing semicolon when it is printed vertically:
428 [
431 a;
432 b;
433 c;
434 ]
435 You can do this as follows:
438 printf "@[<v 0>[@;<0 2>@[<v 0>a;@,b;@,c@]%t]@]@\n"
439 (pp_print_custom_break ~fits:("", 0, "") ~breaks:(";", 0, ""))
440 Since 4.08.0
444 val pp_force_newline : formatter -> unit -> unit
448 val force_newline : unit -> unit
453 Force a new line in the current pretty-printing box.
455 The pretty-printer must split the line at this point,
457 Not the normal way of pretty-printing, since imperative line splitting
459 may interfere with current line counters and box size calculation.
460 Using break hints within an enclosing vertical box is a better alterna‐
461 tive.
462 val pp_print_if_newline : formatter -> unit -> unit
466 val print_if_newline : unit -> unit
471 Execute the next formatting command if the preceding line has just been
473 split. Otherwise, ignore the next formatting command.
474 Pretty-printing termination
479 val pp_print_flush : formatter -> unit -> unit
480 val print_flush : unit -> unit
485 End of pretty-printing: resets the pretty-printer to initial state.
487 All open pretty-printing boxes are closed, all pending text is printed.
489 In addition, the pretty-printer low level output device is flushed to
490 ensure that all pending text is really displayed.
491 Note: never use print_flush in the normal course of a pretty-printing
493 routine, since the pretty-printer uses a complex buffering machinery to
494 properly indent the output; manually flushing those buffers at random
495 would conflict with the pretty-printer strategy and result to poor ren‐
496 dering.
497 Only consider using print_flush when displaying all pending material is
499 mandatory (for instance in case of interactive use when you want the
500 user to read some text) and when resetting the pretty-printer state
501 will not disturb further pretty-printing.
502 Warning: If the output device of the pretty-printer is an output chan‐
504 nel, repeated calls to print_flush means repeated calls to flush to
505 flush the out channel; these explicit flush calls could foil the
506 buffering strategy of output channels and could dramatically impact
507 efficiency.
508 val pp_print_newline : formatter -> unit -> unit
512 val print_newline : unit -> unit
517 End of pretty-printing: resets the pretty-printer to initial state.
519 All open pretty-printing boxes are closed, all pending text is printed.
521 Equivalent to Format.print_flush followed by a new line. See corre‐
523 sponding words of caution for Format.print_flush .
524 Note: this is not the normal way to output a new line; the preferred
526 method is using break hints within a vertical pretty-printing box.
527 Margin
532 val pp_set_margin : formatter -> int -> unit
533 val set_margin : int -> unit
538 pp_set_margin ppf d sets the right margin to d (in characters): the
541 pretty-printer splits lines that overflow the right margin according to
542 the break hints given. Nothing happens if d is smaller than 2. If d
543 is too large, the right margin is set to the maximum admissible value
544 (which is greater than 10 ^ 9 ). If d is less than the current maximum
545 indentation limit, the maximum indentation limit is decreased while
546 trying to preserve a minimal ratio max_indent/margin>=50% and if possi‐
547 ble the current difference margin - max_indent .
548 See also Format.pp_set_geometry .
550 val pp_get_margin : formatter -> unit -> int
554 val get_margin : unit -> int
559 Returns the position of the right margin.
561 Maximum indentation limit
566 val pp_set_max_indent : formatter -> int -> unit
567 val set_max_indent : int -> unit
572 pp_set_max_indent ppf d sets the maximum indentation limit of lines to
575 d (in characters): once this limit is reached, new pretty-printing
576 boxes are rejected to the left, unless the enclosing box fully fits on
577 the current line. As an illustration,
578 set_margin 10; set_max_indent 5; printf "@[123456@[7@]89A@]@."
579 yields
580 123456
581 789A
582 because the nested box "@[7@]" is opened after the maximum indentation
584 limit ( 7>5 ) and its parent box does not fit on the current line.
585 Either decreasing the length of the parent box to make it fit on a
586 line:
587 printf "@[123456@[7@]89@]@."
588 or opening an intermediary box before the maximum indentation limit
589 which fits on the current line
590 printf "@[123@[456@[7@]89@]A@]@."
591 avoids the rejection to the left of the inner boxes and print respec‐
592 tively "123456789" and "123456789A" . Note also that vertical boxes
593 never fit on a line whereas horizontal boxes always fully fit on the
594 current line.
595 Nothing happens if d is smaller than 2.
597 If d is too large, the limit is set to the maximum admissible value
599 (which is greater than 10 ^ 9 ).
600 If d is greater or equal than the current margin, it is ignored, and
602 the current maximum indentation limit is kept.
603 See also Format.pp_set_geometry .
605 val pp_get_max_indent : formatter -> unit -> int
609 val get_max_indent : unit -> int
614 Return the maximum indentation limit (in characters).
616 Geometry
621 Geometric functions can be used to manipulate simultaneously the cou‐
622 pled variables, margin and maxixum indentation limit.
623 type geometry = {
625 max_indent : int ;
626 margin : int ;
627 }
628 val check_geometry : geometry -> bool
634 Check if the formatter geometry is valid: 1 < max_indent < margin
636 val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
641 val set_geometry : max_indent:int -> margin:int -> unit
646 val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int ->
651 unit
652 val safe_set_geometry : max_indent:int -> margin:int -> unit
657 pp_set_geometry ppf ~max_indent ~margin sets both the margin and maxi‐
660 mum indentation limit for ppf .
661 When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin
663 is equivalent to pp_set_margin ppf margin; pp_set_max_indent ppf
664 max_indent ; and avoids the subtly incorrect pp_set_max_indent ppf
665 max_indent; pp_set_margin ppf margin ;
666 Outside of this domain, pp_set_geometry raises an invalid argument
668 exception whereas pp_safe_set_geometry does nothing.
669 Since 4.08.0
672 val pp_get_geometry : formatter -> unit -> geometry
676 val get_geometry : unit -> geometry
681 Return the current geometry of the formatter
683 Since 4.08.0
686 Maximum formatting depth
691 The maximum formatting depth is the maximum number of pretty-printing
692 boxes simultaneously open.
693 Material inside boxes nested deeper is printed as an ellipsis (more
695 precisely as the text returned by Format.get_ellipsis_text () ).
696 val pp_set_max_boxes : formatter -> int -> unit
698 val set_max_boxes : int -> unit
703 pp_set_max_boxes ppf max sets the maximum number of pretty-printing
706 boxes simultaneously open.
707 Material inside boxes nested deeper is printed as an ellipsis (more
709 precisely as the text returned by Format.get_ellipsis_text () ).
710 Nothing happens if max is smaller than 2.
712 val pp_get_max_boxes : formatter -> unit -> int
716 val get_max_boxes : unit -> int
721 Returns the maximum number of pretty-printing boxes allowed before
723 ellipsis.
724 val pp_over_max_boxes : formatter -> unit -> bool
728 val over_max_boxes : unit -> bool
733 Tests if the maximum number of pretty-printing boxes allowed have
735 already been opened.
736 Tabulation boxes
741 A tabulation box prints material on lines divided into cells of fixed
742 length. A tabulation box provides a simple way to display vertical col‐
743 umns of left adjusted text.
744 This box features command set_tab to define cell boundaries, and com‐
746 mand print_tab to move from cell to cell and split the line when there
747 is no more cells to print on the line.
748 Note: printing within tabulation box is line directed, so arbitrary
750 line splitting inside a tabulation box leads to poor rendering. Yet,
751 controlled use of tabulation boxes allows simple printing of columns
752 within module Format .
753 val pp_open_tbox : formatter -> unit -> unit
755 val open_tbox : unit -> unit
760 open_tbox () opens a new tabulation box.
763 This box prints lines separated into cells of fixed width.
765 Inside a tabulation box, special tabulation markers defines points of
767 interest on the line (for instance to delimit cell boundaries). Func‐
768 tion Format.set_tab sets a tabulation marker at insertion point.
769 A tabulation box features specific tabulation breaks to move to next
771 tabulation marker or split the line. Function Format.print_tbreak
772 prints a tabulation break.
773 val pp_close_tbox : formatter -> unit -> unit
777 val close_tbox : unit -> unit
782 Closes the most recently opened tabulation box.
784 val pp_set_tab : formatter -> unit -> unit
788 val set_tab : unit -> unit
793 Sets a tabulation marker at current insertion point.
795 val pp_print_tab : formatter -> unit -> unit
799 val print_tab : unit -> unit
804 print_tab () emits a 'next' tabulation break hint: if not already set
807 on a tabulation marker, the insertion point moves to the first tabula‐
808 tion marker on the right, or the pretty-printer splits the line and
809 insertion point moves to the leftmost tabulation marker.
810 It is equivalent to print_tbreak 0 0 .
812 val pp_print_tbreak : formatter -> int -> int -> unit
816 val print_tbreak : int -> int -> unit
821 print_tbreak nspaces offset emits a 'full' tabulation break hint.
824 If not already set on a tabulation marker, the insertion point moves to
826 the first tabulation marker on the right and the pretty-printer prints
827 nspaces spaces.
828 If there is no next tabulation marker on the right, the pretty-printer
830 splits the line at this point, then insertion point moves to the left‐
831 most tabulation marker of the box.
832 If the pretty-printer splits the line, offset is added to the current
834 indentation.
835 Ellipsis
840 val pp_set_ellipsis_text : formatter -> string -> unit
841 val set_ellipsis_text : string -> unit
846 Set the text of the ellipsis printed when too many pretty-printing
848 boxes are open (a single dot, . , by default).
849 val pp_get_ellipsis_text : formatter -> unit -> string
853 val get_ellipsis_text : unit -> string
858 Return the text of the ellipsis.
860 Semantic tags
865 type stag = ..
866 Semantic tags (or simply tags) are user's defined annotations to asso‐
869 ciate user's specific operations to printed entities.
870 Common usage of semantic tags is text decoration to get specific font
872 or text size rendering for a display device, or marking delimitation of
873 entities (e.g. HTML or TeX elements or terminal escape sequences).
874 More sophisticated usage of semantic tags could handle dynamic modifi‐
875 cation of the pretty-printer behavior to properly print the material
876 within some specific tags. For instance, we can define an RGB tag like
877 so:
878 type stag += RGB of {r:int;g:int;b:int}
879 In order to properly delimit printed entities, a semantic tag must be
882 opened before and closed after the entity. Semantic tags must be prop‐
883 erly nested like parentheses using Format.pp_open_stag and For‐
884 mat.pp_close_stag .
885 Tag specific operations occur any time a tag is opened or closed, At
887 each occurrence, two kinds of operations are performed tag-marking and
888 tag-printing:
889 -The tag-marking operation is the simpler tag specific operation: it
891 simply writes a tag specific string into the output device of the for‐
892 matter. Tag-marking does not interfere with line-splitting computation.
893 -The tag-printing operation is the more involved tag specific opera‐
895 tion: it can print arbitrary material to the formatter. Tag-printing is
896 tightly linked to the current pretty-printer operations.
897 Roughly speaking, tag-marking is commonly used to get a better render‐
899 ing of texts in the rendering device, while tag-printing allows fine
900 tuning of printing routines to print the same entity differently
901 according to the semantic tags (i.e. print additional material or even
902 omit parts of the output).
903 More precisely: when a semantic tag is opened or closed then both and
905 successive 'tag-printing' and 'tag-marking' operations occur:
906 -Tag-printing a semantic tag means calling the formatter specific func‐
908 tion print_open_stag (resp. print_close_stag ) with the name of the
909 tag as argument: that tag-printing function can then print any regular
910 material to the formatter (so that this material is enqueued as usual
911 in the formatter queue for further line splitting computation).
912 -Tag-marking a semantic tag means calling the formatter specific func‐
914 tion mark_open_stag (resp. mark_close_stag ) with the name of the tag
915 as argument: that tag-marking function can then return the 'tag-opening
916 marker' (resp. `tag-closing marker') for direct output into the output
917 device of the formatter.
918 Being written directly into the output device of the formatter, seman‐
920 tic tag marker strings are not considered as part of the printing mate‐
921 rial that drives line splitting (in other words, the length of the
922 strings corresponding to tag markers is considered as zero for line
923 splitting).
924 Thus, semantic tag handling is in some sense transparent to
926 pretty-printing and does not interfere with usual indentation. Hence, a
927 single pretty-printing routine can output both simple 'verbatim' mate‐
928 rial or richer decorated output depending on the treatment of tags. By
929 default, tags are not active, hence the output is not decorated with
930 tag information. Once set_tags is set to true , the pretty-printer
931 engine honors tags and decorates the output accordingly.
932 Default tag-marking functions behave the HTML way: Format.tag are
934 enclosed in "<" and ">" while other tags are ignored; hence, opening
935 marker for tag string "t" is "<t>" and closing marker is "</t>" .
936 Default tag-printing functions just do nothing.
938 Tag-marking and tag-printing functions are user definable and can be
940 set by calling Format.set_formatter_stag_functions .
941 Semantic tag operations may be set on or off with Format.set_tags .
943 Tag-marking operations may be set on or off with Format.set_mark_tags .
944 Tag-printing operations may be set on or off with Format.set_print_tags
945 .
946 type tag = string
949 type stag +=
954 | String_tag of tag (* String_tag s is a string tag s . String tags
955 can be inserted either by explicitly using the constructor String_tag
956 or by using the dedicated format syntax "@{<s> ... @}" .
957 *)
958 val pp_open_stag : formatter -> stag -> unit
964 val open_stag : stag -> unit
969 pp_open_stag ppf t opens the semantic tag named t .
972 The print_open_stag tag-printing function of the formatter is called
974 with t as argument; then the opening tag marker for t , as given by
975 mark_open_stag t , is written into the output device of the formatter.
976 val pp_close_stag : formatter -> unit -> unit
980 val close_stag : unit -> unit
985 pp_close_stag ppf () closes the most recently opened semantic tag t .
988 The closing tag marker, as given by mark_close_stag t , is written into
990 the output device of the formatter; then the print_close_stag
991 tag-printing function of the formatter is called with t as argument.
992 val pp_set_tags : formatter -> bool -> unit
996 val set_tags : bool -> unit
1001 pp_set_tags ppf b turns on or off the treatment of semantic tags
1004 (default is off).
1005 val pp_set_print_tags : formatter -> bool -> unit
1009 val set_print_tags : bool -> unit
1014 pp_set_print_tags ppf b turns on or off the tag-printing operations.
1017 val pp_set_mark_tags : formatter -> bool -> unit
1021 val set_mark_tags : bool -> unit
1026 pp_set_mark_tags ppf b turns on or off the tag-marking operations.
1029 val pp_get_print_tags : formatter -> unit -> bool
1033 val get_print_tags : unit -> bool
1038 Return the current status of tag-printing operations.
1040 val pp_get_mark_tags : formatter -> unit -> bool
1044 val get_mark_tags : unit -> bool
1049 Return the current status of tag-marking operations.
1051 val pp_set_formatter_out_channel : formatter -> out_channel -> unit
1055 Redirecting the standard formatter output
1058 val set_formatter_out_channel : out_channel -> unit
1059 Redirect the standard pretty-printer output to the given channel. (All
1061 the output functions of the standard formatter are set to the default
1062 output functions printing to the given channel.)
1063 set_formatter_out_channel is equivalent to Format.pp_set_format‐
1066 ter_out_channel std_formatter .
1067 val pp_set_formatter_output_functions : formatter -> (string -> int ->
1071 int -> unit) -> (unit -> unit) -> unit
1072 val set_formatter_output_functions : (string -> int -> int -> unit) ->
1077 (unit -> unit) -> unit
1078 pp_set_formatter_output_functions ppf out flush redirects the standard
1081 pretty-printer output functions to the functions out and flush .
1082 The out function performs all the pretty-printer string output. It is
1084 called with a string s , a start position p , and a number of charac‐
1085 ters n ; it is supposed to output characters p to p + n - 1 of s .
1086 The flush function is called whenever the pretty-printer is flushed
1088 (via conversion %! , or pretty-printing indications @? or @. , or
1089 using low level functions print_flush or print_newline ).
1090 val pp_get_formatter_output_functions : formatter -> unit -> (string ->
1094 int -> int -> unit) * (unit -> unit)
1095 val get_formatter_output_functions : unit -> (string -> int -> int ->
1100 unit) * (unit -> unit)
1101 Return the current output functions of the standard pretty-printer.
1103 Redefining formatter output
1108 The Format module is versatile enough to let you completely redefine
1109 the meaning of pretty-printing output: you may provide your own func‐
1110 tions to define how to handle indentation, line splitting, and even
1111 printing of all the characters that have to be printed!
1112 Redefining output functions
1114 type formatter_out_functions = {
1115 out_string : string -> int -> int -> unit ;
1116 out_flush : unit -> unit ;
1117 out_newline : unit -> unit ;
1118 out_spaces : int -> unit ;
1119 out_indent : int -> unit ;
1120 }
1121 The set of output functions specific to a formatter:
1124 -the out_string function performs all the pretty-printer string output.
1126 It is called with a string s , a start position p , and a number of
1127 characters n ; it is supposed to output characters p to p + n - 1 of s
1128 .
1129 -the out_flush function flushes the pretty-printer output device.
1131 - out_newline is called to open a new line when the pretty-printer
1133 splits the line.
1134 -the out_spaces function outputs spaces when a break hint leads to spa‐
1136 ces instead of a line split. It is called with the number of spaces to
1137 output.
1138 -the out_indent function performs new line indentation when the
1140 pretty-printer splits the line. It is called with the indentation value
1141 of the new line.
1142 By default:
1144 -fields out_string and out_flush are output device specific; (e.g.
1146 output_string and flush for a out_channel device, or Buffer.add_sub‐
1147 string and ignore for a Buffer.t output device),
1148 -field out_newline is equivalent to out_string "\n" 0 1 ;
1150 -fields out_spaces and out_indent are equivalent to out_string
1152 (String.make n ' ') 0 n .
1153 Since 4.01.0
1157 val pp_set_formatter_out_functions : formatter -> formatter_out_func‐
1161 tions -> unit
1162 val set_formatter_out_functions : formatter_out_functions -> unit
1167 pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer
1170 output functions of ppf to those of argument out_funs ,
1171 This way, you can change the meaning of indentation (which can be some‐
1173 thing else than just printing space characters) and the meaning of new
1174 lines opening (which can be connected to any other action needed by the
1175 application at hand).
1176 Reasonable defaults for functions out_spaces and out_newline are
1178 respectively out_funs.out_string (String.make n ' ') 0 n and
1179 out_funs.out_string "\n" 0 1 .
1180 Since 4.01.0
1183 val pp_get_formatter_out_functions : formatter -> unit -> format‐
1187 ter_out_functions
1188 val get_formatter_out_functions : unit -> formatter_out_functions
1193 Return the current output functions of the pretty-printer, including
1195 line splitting and indentation functions. Useful to record the current
1196 setting and restore it afterwards.
1197 Since 4.01.0
1200 Redefining semantic tag operations
1205 type formatter_stag_functions = {
1206 mark_open_stag : stag -> string ;
1207 mark_close_stag : stag -> string ;
1208 print_open_stag : stag -> unit ;
1209 print_close_stag : stag -> unit ;
1210 }
1211 The semantic tag handling functions specific to a formatter: mark ver‐
1214 sions are the 'tag-marking' functions that associate a string marker to
1215 a tag in order for the pretty-printing engine to write those markers as
1216 0 length tokens in the output device of the formatter. print versions
1217 are the 'tag-printing' functions that can perform regular printing when
1218 a tag is closed or opened.
1219 val pp_set_formatter_stag_functions : formatter -> formatter_stag_func‐
1223 tions -> unit
1224 val set_formatter_stag_functions : formatter_stag_functions -> unit
1229 pp_set_formatter_stag_functions ppf tag_funs changes the meaning of
1232 opening and closing semantic tag operations to use the functions in
1233 tag_funs when printing on ppf .
1234 When opening a semantic tag with name t , the string t is passed to the
1236 opening tag-marking function (the mark_open_stag field of the record
1237 tag_funs ), that must return the opening tag marker for that name. When
1238 the next call to close_stag () happens, the semantic tag name t is sent
1239 back to the closing tag-marking function (the mark_close_stag field of
1240 record tag_funs ), that must return a closing tag marker for that name.
1241 The print_ field of the record contains the tag-printing functions that
1243 are called at tag opening and tag closing time, to output regular mate‐
1244 rial in the pretty-printer queue.
1245 val pp_get_formatter_stag_functions : formatter -> unit -> format‐
1249 ter_stag_functions
1250 val get_formatter_stag_functions : unit -> formatter_stag_functions
1255 Return the current semantic tag operation functions of the standard
1257 pretty-printer.
1258 Defining formatters
1263 Defining new formatters permits unrelated output of material in paral‐
1264 lel on several output devices. All the parameters of a formatter are
1265 local to the formatter: right margin, maximum indentation limit, maxi‐
1266 mum number of pretty-printing boxes simultaneously open, ellipsis, and
1267 so on, are specific to each formatter and may be fixed independently.
1268 For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b
1270 returns a new formatter using buffer b as its output device. Simi‐
1271 larly, given a out_channel output channel oc , Format.format‐
1272 ter_of_out_channel oc returns a new formatter using channel oc as its
1273 output device.
1274 Alternatively, given out_funs , a complete set of output functions for
1276 a formatter, then Format.formatter_of_out_functions out_funs computes a
1277 new formatter using those functions for output.
1278 val formatter_of_out_channel : out_channel -> formatter
1280 formatter_of_out_channel oc returns a new formatter writing to the cor‐
1283 responding output channel oc .
1284 val std_formatter : formatter
1288 The standard formatter to write to standard output.
1290 It is defined as Format.formatter_of_out_channel stdout .
1292 val err_formatter : formatter
1296 A formatter to write to standard error.
1298 It is defined as Format.formatter_of_out_channel stderr .
1300 val formatter_of_buffer : Buffer.t -> formatter
1304 formatter_of_buffer b returns a new formatter writing to buffer b . At
1307 the end of pretty-printing, the formatter must be flushed using For‐
1308 mat.pp_print_flush or Format.pp_print_newline , to print all the pend‐
1309 ing material into the buffer.
1310 val stdbuf : Buffer.t
1314 The string buffer in which str_formatter writes.
1316 val str_formatter : formatter
1320 A formatter to output to the Format.stdbuf string buffer.
1322 str_formatter is defined as Format.formatter_of_buffer Format.stdbuf .
1325 val flush_str_formatter : unit -> string
1329 Returns the material printed with str_formatter , flushes the formatter
1331 and resets the corresponding buffer.
1332 val make_formatter : (string -> int -> int -> unit) -> (unit -> unit)
1336 -> formatter
1337 make_formatter out flush returns a new formatter that outputs with
1340 function out , and flushes with function flush .
1341 For instance,
1343 make_formatter
1344 (Stdlib.output oc)
1345 (fun () -> Stdlib.flush oc)
1346 returns a formatter to the out_channel oc .
1347 val formatter_of_out_functions : formatter_out_functions -> formatter
1351 formatter_of_out_functions out_funs returns a new formatter that writes
1354 with the set of output functions out_funs .
1355 See definition of type Format.formatter_out_functions for the meaning
1357 of argument out_funs .
1358 Since 4.06.0
1361 Symbolic pretty-printing
1366 Symbolic pretty-printing is pretty-printing using a symbolic formatter,
1367 i.e. a formatter that outputs symbolic pretty-printing items.
1368 When using a symbolic formatter, all regular pretty-printing activities
1370 occur but output material is symbolic and stored in a buffer of output
1371 items. At the end of pretty-printing, flushing the output buffer
1372 allows post-processing of symbolic output before performing low level
1373 output operations.
1374 In practice, first define a symbolic output buffer b using:
1376 - let sob = make_symbolic_output_buffer () . Then define a symbolic
1378 formatter with:
1379 - let ppf = formatter_of_symbolic_output_buffer sob
1381 Use symbolic formatter ppf as usual, and retrieve symbolic items at end
1383 of pretty-printing by flushing symbolic output buffer sob with:
1384 - flush_symbolic_output_buffer sob .
1386 type symbolic_output_item =
1389 | Output_flush (* symbolic flush command
1390 *)
1391 | Output_newline (* symbolic newline command
1392 *)
1393 | Output_string of string
1394 (* Output_string s : symbolic output for string s
1395 *)
1397 | Output_spaces of int
1398 (* Output_spaces n : symbolic command to output n spaces
1399 *)
1400 | Output_indent of int
1401 (* Output_indent i : symbolic indentation of size i
1402 *)
1404 Items produced by symbolic pretty-printers
1407 Since 4.06.0
1410 type symbolic_output_buffer
1413 The output buffer of a symbolic pretty-printer.
1416 Since 4.06.0
1419 val make_symbolic_output_buffer : unit -> symbolic_output_buffer
1423 make_symbolic_output_buffer () returns a fresh buffer for symbolic out‐
1426 put.
1427 Since 4.06.0
1430 val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
1434 clear_symbolic_output_buffer sob resets buffer sob .
1437 Since 4.06.0
1440 val get_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1444 bolic_output_item list
1445 get_symbolic_output_buffer sob returns the contents of buffer sob .
1448 Since 4.06.0
1451 val flush_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1455 bolic_output_item list
1456 flush_symbolic_output_buffer sob returns the contents of buffer sob and
1459 resets buffer sob . flush_symbolic_output_buffer sob is equivalent to
1460 let items = get_symbolic_output_buffer sob in
1461 clear_symbolic_output_buffer sob; items
1462 Since 4.06.0
1466 val add_symbolic_output_item : symbolic_output_buffer -> symbolic_out‐
1470 put_item -> unit
1471 add_symbolic_output_item sob itm adds item itm to buffer sob .
1474 Since 4.06.0
1477 val formatter_of_symbolic_output_buffer : symbolic_output_buffer ->
1481 formatter
1482 formatter_of_symbolic_output_buffer sob returns a symbolic formatter
1485 that outputs to symbolic_output_buffer sob .
1486 Since 4.06.0
1489 Convenience formatting functions.
1494 val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter
1495 -> 'a -> unit) -> formatter -> 'a list -> unit
1496 pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to
1499 print each item, and calling pp_sep between items ( pp_sep defaults to
1500 Format.pp_print_cut . Does nothing on empty lists.
1501 Since 4.02.0
1504 val pp_print_text : formatter -> string -> unit
1508 pp_print_text ppf s prints s with spaces and newlines respectively
1511 printed using Format.pp_print_space and Format.pp_force_newline .
1512 Since 4.02.0
1515 val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter
1519 -> 'a -> unit) -> formatter -> 'a option -> unit
1520 pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is
1523 Some v and none if it is None . none prints nothing by default.
1524 Since 4.08
1527 val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter
1531 -> 'e -> unit) -> formatter -> ('a, 'e) result -> unit
1532 pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _
1535 and error if r is Error _ .
1536 Since 4.08
1539 Formatted pretty-printing
1544 Module Format provides a complete set of printf like functions for
1545 pretty-printing using format string specifications.
1546 Specific annotations may be added in the format strings to give
1548 pretty-printing commands to the pretty-printing engine.
1549 Those annotations are introduced in the format strings using the @
1551 character. For instance, @ means a space break, @, means a cut, @[
1552 opens a new box, and @] closes the last open box.
1553 val fprintf : formatter -> ('a, formatter, unit) format -> 'a
1555 fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN accord‐
1561 ing to the format string fmt , and outputs the resulting string on the
1562 formatter ff .
1563 The format string fmt is a character string which contains three types
1565 of objects: plain characters and conversion specifications as specified
1566 in the Printf module, and pretty-printing indications specific to the
1567 Format module.
1568 The pretty-printing indication characters are introduced by a @ charac‐
1570 ter, and their meanings are:
1571 - @[ : open a pretty-printing box. The type and offset of the box may
1573 be optionally specified with the following syntax: the < character,
1574 followed by an optional box type indication, then an optional integer
1575 offset, and the closing > character. Pretty-printing box type is one
1576 of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
1577 pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box,
1578 ' hv ' stands for an 'horizontal/vertical' pretty-printing box, ' b '
1579 stands for an 'horizontal-or-vertical' pretty-printing box demonstrat‐
1580 ing indentation, ' hov ' stands a simple 'horizontal-or-vertical'
1581 pretty-printing box. For instance, @[<hov 2> opens an 'horizon‐
1582 tal-or-vertical' pretty-printing box with indentation 2 as obtained
1583 with open_hovbox 2 . For more details about pretty-printing boxes, see
1584 the various box opening functions open_*box .
1585 - @] : close the most recently opened pretty-printing box.
1587 - @, : output a 'cut' break hint, as with print_cut () .
1589 - @ : output a 'space' break hint, as with print_space () .
1591 - @; : output a 'full' break hint as with print_break . The nspaces and
1593 offset parameters of the break hint may be optionally specified with
1594 the following syntax: the < character, followed by an integer nspaces
1595 value, then an integer offset , and a closing > character. If no
1596 parameters are provided, the good break defaults to a 'space' break
1597 hint.
1598 - @. : flush the pretty-printer and split the line, as with print_new‐
1600 line () .
1601 - @<n> : print the following item as if it were of length n . Hence,
1603 printf "@<0>%s" arg prints arg as a zero length string. If @<n> is not
1604 followed by a conversion specification, then the following character of
1605 the format is printed as if it were of length n .
1606 - @{ : open a semantic tag. The name of the tag may be optionally spec‐
1608 ified with the following syntax: the < character, followed by an
1609 optional string specification, and the closing > character. The string
1610 specification is any character string that does not contain the closing
1611 character '>' . If omitted, the tag name defaults to the empty string.
1612 For more details about semantic tags, see the functions For‐
1613 mat.open_stag and Format.close_stag .
1614 - @} : close the most recently opened semantic tag.
1616 - @? : flush the pretty-printer as with print_flush () . This is
1618 equivalent to the conversion %! .
1619 - @\n : force a newline, as with force_newline () , not the normal way
1621 of pretty-printing, you should prefer using break hints inside a verti‐
1622 cal pretty-printing box.
1623 Note: To prevent the interpretation of a @ character as a pretty-print‐
1625 ing indication, escape it with a % character. Old quotation mode @@ is
1626 deprecated since it is not compatible with formatted input interpreta‐
1627 tion of character '@' .
1628 Example: printf "@[%s@ %d@]@." "x =" 1 is equivalent to open_box ();
1630 print_string "x ="; print_space ();
1631 print_int 1; close_box (); print_newline () . It prints x = 1
1632 within a pretty-printing 'horizontal-or-vertical' box.
1633 val printf : ('a, formatter, unit) format -> 'a
1635 Same as fprintf above, but output on std_formatter .
1637 val eprintf : ('a, formatter, unit) format -> 'a
1641 Same as fprintf above, but output on err_formatter .
1643 val sprintf : ('a, unit, string) format -> 'a
1647 Same as printf above, but instead of printing on a formatter, returns a
1649 string containing the result of formatting the arguments. Note that
1650 the pretty-printer queue is flushed at the end of each call to sprintf
1651 .
1652 In case of multiple and related calls to sprintf to output material on
1654 a single string, you should consider using fprintf with the predefined
1655 formatter str_formatter and call flush_str_formatter () to get the
1656 final result.
1657 Alternatively, you can use Format.fprintf with a formatter writing to a
1659 buffer of your own: flushing the formatter and the buffer at the end of
1660 pretty-printing returns the desired string.
1661 val asprintf : ('a, formatter, unit, string) format4 -> 'a
1665 Same as printf above, but instead of printing on a formatter, returns a
1667 string containing the result of formatting the arguments. The type of
1668 asprintf is general enough to interact nicely with %a conversions.
1669 Since 4.01.0
1672 val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
1676 Same as Format.fprintf , except the formatter is the last argument.
1678 dprintf "..." a b c is a function of type formatter -> unit which can
1679 be given to a format specifier %t .
1680 This can be used as a replacement for Format.asprintf to delay format‐
1682 ting decisions. Using the string returned by Format.asprintf in a for‐
1683 matting context forces formatting decisions to be taken in isolation,
1684 and the final string may be created prematurely. Format.dprintf allows
1685 delay of formatting decisions until the final formatting context is
1686 known. For example:
1687 let t = Format.dprintf "%i@ %i@ %i" 1 2 3 in
1688 ...
1689 Format.printf "@[<v>%t@]" t
1690 Since 4.08.0
1694 val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
1698 Same as fprintf above, but does not print anything. Useful to ignore
1700 some material when conditionally printing.
1701 Since 3.10.0
1704 Formatted Pretty-Printing with continuations.
1709 val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1711 'a) format4 -> 'b
1712 Same as fprintf above, but instead of returning immediately, passes the
1714 formatter to its first argument at the end of printing.
1715 val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a)
1719 format4 -> 'b
1720 Same as Format.dprintf above, but instead of returning immediately,
1722 passes the suspended printer to its first argument at the end of print‐
1723 ing.
1724 Since 4.08.0
1727 val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1731 'a) format4 -> 'b
1732 Same as kfprintf above, but does not print anything. Useful to ignore
1734 some material when conditionally printing.
1735 Since 3.12.0
1738 val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1742 Same as sprintf above, but instead of returning the string, passes it
1744 to the first argument.
1745 val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 ->
1749 'b
1750 Same as asprintf above, but instead of returning the string, passes it
1752 to the first argument.
1753 Since 4.03
1756 Deprecated
1761 val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
1762 Deprecated. This function is error prone. Do not use it. This func‐
1764 tion is neither compositional nor incremental, since it flushes the
1765 pretty-printer queue at each call.
1766 If you need to print to some buffer b , you must first define a format‐
1768 ter writing to b , using let to_b = formatter_of_buffer b ; then use
1769 regular calls to Format.fprintf with formatter to_b .
1770 val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1774 Deprecated. An alias for ksprintf .
1776 val set_all_formatter_output_functions : out:(string -> int -> int ->
1780 unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int
1781 -> unit) -> unit
1782 Deprecated. Subsumed by set_formatter_out_functions .
1784 val get_all_formatter_output_functions : unit -> (string -> int -> int
1788 -> unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
1789 Deprecated. Subsumed by get_formatter_out_functions .
1791 val pp_set_all_formatter_output_functions : formatter -> out:(string ->
1795 int -> int -> unit) -> flush:(unit -> unit) -> newline:(unit -> unit)
1796 -> spaces:(int -> unit) -> unit
1797 Deprecated. Subsumed by pp_set_formatter_out_functions .
1799 val pp_get_all_formatter_output_functions : formatter -> unit ->
1803 (string -> int -> int -> unit) * (unit -> unit) * (unit -> unit) * (int
1804 -> unit)
1805 Deprecated. Subsumed by pp_get_formatter_out_functions .
1807 String tags
1812 val pp_open_tag : formatter -> tag -> unit
1813 Deprecated. Subsumed by Format.pp_open_stag .
1815 val open_tag : tag -> unit
1819 Deprecated. Subsumed by Format.open_stag .
1821 val pp_close_tag : formatter -> unit -> unit
1825 Deprecated. Subsumed by Format.pp_close_stag .
1827 val close_tag : unit -> unit
1831 Deprecated. Subsumed by Format.close_stag .
1833 type formatter_tag_functions = {
1836 mark_open_tag : tag -> string ;
1837 mark_close_tag : tag -> string ;
1838 print_open_tag : tag -> unit ;
1839 print_close_tag : tag -> unit ;
1840 }
1841 Deprecated. Subsumed by Format.formatter_stag_functions .
1844 val pp_set_formatter_tag_functions : formatter -> formatter_tag_func‐
1848 tions -> unit
1849 Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
1851 This function will erase non-string tag formatting functions.
1854 val set_formatter_tag_functions : formatter_tag_functions -> unit
1858 Deprecated. Subsumed by Format.set_formatter_stag_functions .
1860 val pp_get_formatter_tag_functions : formatter -> unit -> format‐
1864 ter_tag_functions
1865 Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
1867 val get_formatter_tag_functions : unit -> formatter_tag_functions
1871 Deprecated. Subsumed by Format.get_formatter_stag_functions .
1873OCamldoc 2020-02-27 Format(3)