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 (); print_int 1; close_box (); print_newline () that prints x = 1
39 within a pretty-printing box, can be abbreviated as printf @[%s@ %i@]@.
40 x = 1 , or even shorter printf @[x =@ %i@]@. 1 .
41 Rule of thumb for casual users of this library:
43 -use simple pretty-printing boxes (as obtained by open_box 0 );
45 -use simple break hints as obtained by print_cut () that outputs a sim‐
47 ple break hint, or by print_space () that outputs a space indicating a
48 break hint;
49 -once a pretty-printing box is open, display its material with basic
51 printing functions (e. g. print_int and print_string );
52 -when the material for a pretty-printing box has been printed, call
54 close_box () to close the box;
55 -at the end of pretty-printing, flush the pretty-printer to display all
57 the remaining material, e.g. evaluate print_newline () .
58 The behavior of pretty-printing commands is unspecified if there is no
60 open pretty-printing box. Each box opened by one of the open_ functions
61 below must be closed using close_box for proper formatting. Otherwise,
62 some of the material printed in the boxes may not be output, or may be
63 formatted incorrectly.
64 In case of interactive use, each phrase is executed in the initial
66 state of the standard pretty-printer: after each phrase execution, the
67 interactive system closes all open pretty-printing boxes, flushes all
68 pending text, and resets the standard pretty-printer.
69 Warning: mixing calls to pretty-printing functions of this module with
71 calls to Stdlib low level output functions is error prone.
72 The pretty-printing functions output material that is delayed in the
74 pretty-printer queue and stacks in order to compute proper line split‐
75 ting. In contrast, basic I/O output functions write directly in their
76 output device. As a consequence, the output of a basic I/O function may
77 appear before the output of a pretty-printing function that has been
78 called before. For instance, Stdlib.print_string < ; For‐
79 mat.print_string PRETTY ; Stdlib.print_string > ; Format.print_string
80 TEXT ; leads to output <>PRETTYTEXT .
81 type formatter
83 Abstract data corresponding to a pretty-printer (also called a format‐
86 ter) and all its machinery. See also Format.formatter .
87 Pretty-printing boxes
92 The pretty-printing engine uses the concepts of pretty-printing box and
93 break hint to drive indentation and line splitting behavior of the
94 pretty-printer.
95 Each different pretty-printing box kind introduces a specific line
97 splitting policy:
98 -within an horizontal box, break hints never split the line (but the
101 line may be split in a box nested deeper),
102 -within a vertical box, break hints always split the line,
104 -within an horizontal/vertical box, if the box fits on the current line
106 then break hints never split the line, otherwise break hint always
107 split the line,
108 -within a compacting box, a break hint never splits the line, unless
110 there is no more room on the current line.
111 Note that line splitting policy is box specific: the policy of a box
113 does not rule the policy of inner boxes. For instance, if a vertical
114 box is nested in an horizontal box, all break hints within the vertical
115 box will split the line.
116 val pp_open_box : formatter -> int -> unit
118 val open_box : int -> unit
123 pp_open_box ppf d opens a new compacting pretty-printing box with off‐
126 set d in the formatter ppf .
127 Within this box, the pretty-printer prints as much as possible material
129 on every line.
130 A break hint splits the line if there is no more room on the line to
132 print the remainder of the box.
133 Within this box, the pretty-printer emphasizes the box structure: a
135 break hint also splits the line if the splitting ``moves to the left''
136 (i.e. the new line gets an indentation smaller than the one of the cur‐
137 rent line).
138 This box is the general purpose pretty-printing box.
140 If the pretty-printer splits the line in the box, offset d is added to
142 the current indentation.
143 val pp_close_box : formatter -> unit -> unit
147 val close_box : unit -> unit
152 Closes the most recently open pretty-printing box.
154 val pp_open_hbox : formatter -> unit -> unit
158 val open_hbox : unit -> unit
163 pp_open_hbox ppf () opens a new 'horizontal' pretty-printing box.
166 This box prints material on a single line.
168 Break hints in a horizontal box never split the line. (Line splitting
170 may still occur inside boxes nested deeper).
171 val pp_open_vbox : formatter -> int -> unit
175 val open_vbox : int -> unit
180 pp_open_vbox ppf d opens a new 'vertical' pretty-printing box with off‐
183 set d .
184 This box prints material on as many lines as break hints in the box.
186 Every break hint in a vertical box splits the line.
188 If the pretty-printer splits the line in the box, d is added to the
190 current indentation.
191 val pp_open_hvbox : formatter -> int -> unit
195 val open_hvbox : int -> unit
200 pp_open_hvbox ppf d opens a new 'horizontal/vertical' pretty-printing
203 box with offset d .
204 This box behaves as an horizontal box if it fits on a single line, oth‐
206 erwise it behaves as a vertical box.
207 If the pretty-printer splits the line in the box, d is added to the
209 current indentation.
210 val pp_open_hovbox : formatter -> int -> unit
214 val open_hovbox : int -> unit
219 pp_open_hovbox ppf d opens a new 'horizontal-or-vertical' pretty-print‐
222 ing box with offset d .
223 This box prints material as much as possible on every line.
225 A break hint splits the line if there is no more room on the line to
227 print the remainder of the box.
228 If the pretty-printer splits the line in the box, d is added to the
230 current indentation.
231 Formatting functions
236 val pp_print_string : formatter -> string -> unit
237 val print_string : string -> unit
242 pp_print_string ppf s prints s in the current pretty-printing box.
245 val pp_print_as : formatter -> int -> string -> unit
249 val print_as : int -> string -> unit
254 pp_print_as ppf len s prints s in the current pretty-printing box. The
257 pretty-printer formats s as if it were of length len .
258 val pp_print_int : formatter -> int -> unit
262 val print_int : int -> unit
267 Print an integer in the current pretty-printing box.
269 val pp_print_float : formatter -> float -> unit
273 val print_float : float -> unit
278 Print a floating point number in the current pretty-printing box.
280 val pp_print_char : formatter -> char -> unit
284 val print_char : char -> unit
289 Print a character in the current pretty-printing box.
291 val pp_print_bool : formatter -> bool -> unit
295 val print_bool : bool -> unit
300 Print a boolean in the current pretty-printing box.
302 Break hints
307 A 'break hint' tells the pretty-printer to output some space or split
308 the line whichever way is more appropriate to the current pretty-print‐
309 ing box splitting rules.
310 Break hints are used to separate printing items and are mandatory to
312 let the pretty-printer correctly split lines and indent items.
313 Simple break hints are:
315 -the 'space': output a space or split the line if appropriate,
317 -the 'cut': split the line if appropriate.
319 Note: the notions of space and line splitting are abstract for the
321 pretty-printing engine, since those notions can be completely redefined
322 by the programmer. However, in the pretty-printer default setting,
323 ``output a space'' simply means printing a space character (ASCII code
324 32) and ``split the line'' means printing a newline character (ASCII
325 code 10).
326 val pp_print_space : formatter -> unit -> unit
328 val print_space : unit -> unit
333 pp_print_space ppf () emits a 'space' break hint: the pretty-printer
336 may split the line at this point, otherwise it prints one space.
337 pp_print_space ppf () is equivalent to pp_print_break ppf 1 0 .
340 val pp_print_cut : formatter -> unit -> unit
344 val print_cut : unit -> unit
349 pp_print_cut ppf () emits a 'cut' break hint: the pretty-printer may
352 split the line at this point, otherwise it prints nothing.
353 pp_print_cut ppf () is equivalent to pp_print_break ppf 0 0 .
356 val pp_print_break : formatter -> int -> int -> unit
360 val print_break : int -> int -> unit
365 pp_print_break ppf nspaces offset emits a 'full' break hint: the
368 pretty-printer may split the line at this point, otherwise it prints
369 nspaces spaces.
370 If the pretty-printer splits the line, offset is added to the current
372 indentation.
373 val pp_print_custom_break : formatter -> fits:string * int * string ->
377 breaks:string * int * string -> unit
378 pp_print_custom_break ppf ~fits:(s1, n, s2) ~breaks:(s3, m, s4) emits a
381 custom break hint: the pretty-printer may split the line at this point.
382 If it does not split the line, then the s1 is emitted, then n spaces,
384 then s2 .
385 If it splits the line, then it emits the s3 string, then an indent
387 (according to the box rules), then an offset of m spaces, then the s4
388 string.
389 While n and m are handled by formatter_out_functions.out_indent , the
391 strings will be handled by formatter_out_functions.out_string . This
392 allows for a custom formatter that handles indentation distinctly, for
393 example, outputs <br/> tags or entities.
394 The custom break is useful if you want to change which visible
396 (non-whitespace) characters are printed in case of break or no break.
397 For example, when printing a list [a; b; c] , you might want to add a
398 trailing semicolon when it is printed vertically:
399 [ a; b; c; ]
402 You can do this as follows: printf @[<v 0>[@;<0 2>@[<v
404 0>a;@,b;@,c@]%t]@]@\n (pp_print_custom_break ~fits:("", 0, )
405 ~breaks:(";", 0, ))
406 Since 4.08.0
410 val pp_force_newline : formatter -> unit -> unit
414 val force_newline : unit -> unit
419 Force a new line in the current pretty-printing box.
421 The pretty-printer must split the line at this point,
423 Not the normal way of pretty-printing, since imperative line splitting
425 may interfere with current line counters and box size calculation.
426 Using break hints within an enclosing vertical box is a better alterna‐
427 tive.
428 val pp_print_if_newline : formatter -> unit -> unit
432 val print_if_newline : unit -> unit
437 Execute the next formatting command if the preceding line has just been
439 split. Otherwise, ignore the next formatting command.
440 Pretty-printing termination
445 val pp_print_flush : formatter -> unit -> unit
446 val print_flush : unit -> unit
451 End of pretty-printing: resets the pretty-printer to initial state.
453 All open pretty-printing boxes are closed, all pending text is printed.
455 In addition, the pretty-printer low level output device is flushed to
456 ensure that all pending text is really displayed.
457 Note: never use print_flush in the normal course of a pretty-printing
459 routine, since the pretty-printer uses a complex buffering machinery to
460 properly indent the output; manually flushing those buffers at random
461 would conflict with the pretty-printer strategy and result to poor ren‐
462 dering.
463 Only consider using print_flush when displaying all pending material is
465 mandatory (for instance in case of interactive use when you want the
466 user to read some text) and when resetting the pretty-printer state
467 will not disturb further pretty-printing.
468 Warning: If the output device of the pretty-printer is an output chan‐
470 nel, repeated calls to print_flush means repeated calls to flush to
471 flush the out channel; these explicit flush calls could foil the
472 buffering strategy of output channels and could dramatically impact
473 efficiency.
474 val pp_print_newline : formatter -> unit -> unit
478 val print_newline : unit -> unit
483 End of pretty-printing: resets the pretty-printer to initial state.
485 All open pretty-printing boxes are closed, all pending text is printed.
487 Equivalent to Format.print_flush followed by a new line. See corre‐
489 sponding words of caution for Format.print_flush .
490 Note: this is not the normal way to output a new line; the preferred
492 method is using break hints within a vertical pretty-printing box.
493 Margin
498 val pp_set_margin : formatter -> int -> unit
499 val set_margin : int -> unit
504 pp_set_margin ppf d sets the right margin to d (in characters): the
507 pretty-printer splits lines that overflow the right margin according to
508 the break hints given. Nothing happens if d is smaller than 2. If d
509 is too large, the right margin is set to the maximum admissible value
510 (which is greater than 10 ^ 9 ). If d is less than the current maximum
511 indentation limit, the maximum indentation limit is decreased while
512 trying to preserve a minimal ratio max_indent/margin>=50% and if possi‐
513 ble the current difference margin - max_indent .
514 See also Format.pp_set_geometry .
516 val pp_get_margin : formatter -> unit -> int
520 val get_margin : unit -> int
525 Returns the position of the right margin.
527 Maximum indentation limit
532 val pp_set_max_indent : formatter -> int -> unit
533 val set_max_indent : int -> unit
538 pp_set_max_indent ppf d sets the maximum indentation limit of lines to
541 d (in characters): once this limit is reached, new pretty-printing
542 boxes are rejected to the left, unless the enclosing box fully fits on
543 the current line. As an illustration, set_margin 10; set_max_indent 5;
544 printf @[123456@[7@]89A@]@. yields 123456 789A because the nested box
545 @[7@] is opened after the maximum indentation limit ( 7>5 ) and its
546 parent box does not fit on the current line. Either decreasing the
547 length of the parent box to make it fit on a line: printf
548 @[123456@[7@]89@]@. or opening an intermediary box before the maximum
549 indentation limit which fits on the current line printf
550 @[123@[456@[7@]89@]A@]@. avoids the rejection to the left of the inner
551 boxes and print respectively 123456789 and 123456789A . Note also that
552 vertical boxes never fit on a line whereas horizontal boxes always
553 fully fit on the current line.
554 Nothing happens if d is smaller than 2.
556 If d is too large, the limit is set to the maximum admissible value
558 (which is greater than 10 ^ 9 ).
559 If d is greater or equal than the current margin, it is ignored, and
561 the current maximum indentation limit is kept.
562 See also Format.pp_set_geometry .
564 val pp_get_max_indent : formatter -> unit -> int
568 val get_max_indent : unit -> int
573 Return the maximum indentation limit (in characters).
575 Geometry
580 Geometric functions can be used to manipulate simultaneously the cou‐
581 pled variables, margin and maxixum indentation limit.
582 type geometry = {
584 max_indent : int ;
585 margin : int ;
586 }
587 val check_geometry : geometry -> bool
593 Check if the formatter geometry is valid: 1 < max_indent < margin
595 val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
600 val set_geometry : max_indent:int -> margin:int -> unit
605 val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int ->
610 unit
611 val safe_set_geometry : max_indent:int -> margin:int -> unit
616 pp_set_geometry ppf ~max_indent ~margin sets both the margin and maxi‐
619 mum indentation limit for ppf .
620 When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin
622 is equivalent to pp_set_margin ppf margin; pp_set_max_indent ppf
623 max_indent ; and avoids the subtly incorrect pp_set_max_indent ppf
624 max_indent; pp_set_margin ppf margin ;
625 Outside of this domain, pp_set_geometry raises an invalid argument
627 exception whereas pp_safe_set_geometry does nothing.
628 Since 4.08.0
631 val pp_get_geometry : formatter -> unit -> geometry
635 val get_geometry : unit -> geometry
640 Return the current geometry of the formatter
642 Since 4.08.0
645 Maximum formatting depth
650 The maximum formatting depth is the maximum number of pretty-printing
651 boxes simultaneously open.
652 Material inside boxes nested deeper is printed as an ellipsis (more
654 precisely as the text returned by Format.get_ellipsis_text () ).
655 val pp_set_max_boxes : formatter -> int -> unit
657 val set_max_boxes : int -> unit
662 pp_set_max_boxes ppf max sets the maximum number of pretty-printing
665 boxes simultaneously open.
666 Material inside boxes nested deeper is printed as an ellipsis (more
668 precisely as the text returned by Format.get_ellipsis_text () ).
669 Nothing happens if max is smaller than 2.
671 val pp_get_max_boxes : formatter -> unit -> int
675 val get_max_boxes : unit -> int
680 Returns the maximum number of pretty-printing boxes allowed before
682 ellipsis.
683 val pp_over_max_boxes : formatter -> unit -> bool
687 val over_max_boxes : unit -> bool
692 Tests if the maximum number of pretty-printing boxes allowed have
694 already been opened.
695 Tabulation boxes
700 A tabulation box prints material on lines divided into cells of fixed
701 length. A tabulation box provides a simple way to display vertical col‐
702 umns of left adjusted text.
703 This box features command set_tab to define cell boundaries, and com‐
705 mand print_tab to move from cell to cell and split the line when there
706 is no more cells to print on the line.
707 Note: printing within tabulation box is line directed, so arbitrary
709 line splitting inside a tabulation box leads to poor rendering. Yet,
710 controlled use of tabulation boxes allows simple printing of columns
711 within module Format .
712 val pp_open_tbox : formatter -> unit -> unit
714 val open_tbox : unit -> unit
719 open_tbox () opens a new tabulation box.
722 This box prints lines separated into cells of fixed width.
724 Inside a tabulation box, special tabulation markers defines points of
726 interest on the line (for instance to delimit cell boundaries). Func‐
727 tion Format.set_tab sets a tabulation marker at insertion point.
728 A tabulation box features specific tabulation breaks to move to next
730 tabulation marker or split the line. Function Format.print_tbreak
731 prints a tabulation break.
732 val pp_close_tbox : formatter -> unit -> unit
736 val close_tbox : unit -> unit
741 Closes the most recently opened tabulation box.
743 val pp_set_tab : formatter -> unit -> unit
747 val set_tab : unit -> unit
752 Sets a tabulation marker at current insertion point.
754 val pp_print_tab : formatter -> unit -> unit
758 val print_tab : unit -> unit
763 print_tab () emits a 'next' tabulation break hint: if not already set
766 on a tabulation marker, the insertion point moves to the first tabula‐
767 tion marker on the right, or the pretty-printer splits the line and
768 insertion point moves to the leftmost tabulation marker.
769 It is equivalent to print_tbreak 0 0 .
771 val pp_print_tbreak : formatter -> int -> int -> unit
775 val print_tbreak : int -> int -> unit
780 print_tbreak nspaces offset emits a 'full' tabulation break hint.
783 If not already set on a tabulation marker, the insertion point moves to
785 the first tabulation marker on the right and the pretty-printer prints
786 nspaces spaces.
787 If there is no next tabulation marker on the right, the pretty-printer
789 splits the line at this point, then insertion point moves to the left‐
790 most tabulation marker of the box.
791 If the pretty-printer splits the line, offset is added to the current
793 indentation.
794 Ellipsis
799 val pp_set_ellipsis_text : formatter -> string -> unit
800 val set_ellipsis_text : string -> unit
805 Set the text of the ellipsis printed when too many pretty-printing
807 boxes are open (a single dot, . , by default).
808 val pp_get_ellipsis_text : formatter -> unit -> string
812 val get_ellipsis_text : unit -> string
817 Return the text of the ellipsis.
819 Semantic tags
824 type stag = ..
825 Semantic tags (or simply tags) are user's defined annotations to asso‐
828 ciate user's specific operations to printed entities.
829 Common usage of semantic tags is text decoration to get specific font
831 or text size rendering for a display device, or marking delimitation of
832 entities (e.g. HTML or TeX elements or terminal escape sequences).
833 More sophisticated usage of semantic tags could handle dynamic modifi‐
834 cation of the pretty-printer behavior to properly print the material
835 within some specific tags. For instance, we can define an RGB tag like
836 so: type stag += RGB of {r:int;g:int;b:int}
837 In order to properly delimit printed entities, a semantic tag must be
839 opened before and closed after the entity. Semantic tags must be prop‐
840 erly nested like parentheses using Format.pp_open_stag and For‐
841 mat.pp_close_stag .
842 Tag specific operations occur any time a tag is opened or closed, At
844 each occurrence, two kinds of operations are performed tag-marking and
845 tag-printing:
846 -The tag-marking operation is the simpler tag specific operation: it
848 simply writes a tag specific string into the output device of the for‐
849 matter. Tag-marking does not interfere with line-splitting computation.
850 -The tag-printing operation is the more involved tag specific opera‐
852 tion: it can print arbitrary material to the formatter. Tag-printing is
853 tightly linked to the current pretty-printer operations.
854 Roughly speaking, tag-marking is commonly used to get a better render‐
856 ing of texts in the rendering device, while tag-printing allows fine
857 tuning of printing routines to print the same entity differently
858 according to the semantic tags (i.e. print additional material or even
859 omit parts of the output).
860 More precisely: when a semantic tag is opened or closed then both and
862 successive 'tag-printing' and 'tag-marking' operations occur:
863 -Tag-printing a semantic tag means calling the formatter specific func‐
865 tion print_open_stag (resp. print_close_stag ) with the name of the
866 tag as argument: that tag-printing function can then print any regular
867 material to the formatter (so that this material is enqueued as usual
868 in the formatter queue for further line splitting computation).
869 -Tag-marking a semantic tag means calling the formatter specific func‐
871 tion mark_open_stag (resp. mark_close_stag ) with the name of the tag
872 as argument: that tag-marking function can then return the 'tag-opening
873 marker' (resp. `tag-closing marker') for direct output into the output
874 device of the formatter.
875 Being written directly into the output device of the formatter, seman‐
877 tic tag marker strings are not considered as part of the printing mate‐
878 rial that drives line splitting (in other words, the length of the
879 strings corresponding to tag markers is considered as zero for line
880 splitting).
881 Thus, semantic tag handling is in some sense transparent to
883 pretty-printing and does not interfere with usual indentation. Hence, a
884 single pretty-printing routine can output both simple 'verbatim' mate‐
885 rial or richer decorated output depending on the treatment of tags. By
886 default, tags are not active, hence the output is not decorated with
887 tag information. Once set_tags is set to true , the pretty-printer
888 engine honors tags and decorates the output accordingly.
889 Default tag-marking functions behave the HTML way: Format.tag are
891 enclosed in "<" and ">" while other tags are ignored; hence, opening
892 marker for tag string t is <t> and closing marker is </t> .
893 Default tag-printing functions just do nothing.
895 Tag-marking and tag-printing functions are user definable and can be
897 set by calling Format.set_formatter_stag_functions .
898 Semantic tag operations may be set on or off with Format.set_tags .
900 Tag-marking operations may be set on or off with Format.set_mark_tags .
901 Tag-printing operations may be set on or off with Format.set_print_tags
902 .
903 type tag = string
906 type Format.stag +=
911 | String_tag of tag (* String_tag s is a string tag s . String tags
912 can be inserted either by explicitly using the constructor String_tag
913 or by using the dedicated format syntax @{<s> ... @} .
914 *)
915 val pp_open_stag : formatter -> stag -> unit
921 val open_stag : stag -> unit
926 pp_open_stag ppf t opens the semantic tag named t .
929 The print_open_stag tag-printing function of the formatter is called
931 with t as argument; then the opening tag marker for t , as given by
932 mark_open_stag t , is written into the output device of the formatter.
933 val pp_close_stag : formatter -> unit -> unit
937 val close_stag : unit -> unit
942 pp_close_stag ppf () closes the most recently opened semantic tag t .
945 The closing tag marker, as given by mark_close_stag t , is written into
947 the output device of the formatter; then the print_close_stag
948 tag-printing function of the formatter is called with t as argument.
949 val pp_set_tags : formatter -> bool -> unit
953 val set_tags : bool -> unit
958 pp_set_tags ppf b turns on or off the treatment of semantic tags
961 (default is off).
962 val pp_set_print_tags : formatter -> bool -> unit
966 val set_print_tags : bool -> unit
971 pp_set_print_tags ppf b turns on or off the tag-printing operations.
974 val pp_set_mark_tags : formatter -> bool -> unit
978 val set_mark_tags : bool -> unit
983 pp_set_mark_tags ppf b turns on or off the tag-marking operations.
986 val pp_get_print_tags : formatter -> unit -> bool
990 val get_print_tags : unit -> bool
995 Return the current status of tag-printing operations.
997 val pp_get_mark_tags : formatter -> unit -> bool
1001 val get_mark_tags : unit -> bool
1006 Return the current status of tag-marking operations.
1008 val pp_set_formatter_out_channel : formatter -> out_channel -> unit
1012 Redirecting the standard formatter output
1015 val set_formatter_out_channel : out_channel -> unit
1016 Redirect the standard pretty-printer output to the given channel. (All
1018 the output functions of the standard formatter are set to the default
1019 output functions printing to the given channel.)
1020 set_formatter_out_channel is equivalent to Format.pp_set_format‐
1023 ter_out_channel std_formatter .
1024 val pp_set_formatter_output_functions : formatter -> (string -> int ->
1028 int -> unit) -> (unit -> unit) -> unit
1029 val set_formatter_output_functions : (string -> int -> int -> unit) ->
1034 (unit -> unit) -> unit
1035 pp_set_formatter_output_functions ppf out flush redirects the standard
1038 pretty-printer output functions to the functions out and flush .
1039 The out function performs all the pretty-printer string output. It is
1041 called with a string s , a start position p , and a number of charac‐
1042 ters n ; it is supposed to output characters p to p + n - 1 of s .
1043 The flush function is called whenever the pretty-printer is flushed
1045 (via conversion %! , or pretty-printing indications @? or @. , or
1046 using low level functions print_flush or print_newline ).
1047 val pp_get_formatter_output_functions : formatter -> unit -> (string ->
1051 int -> int -> unit) * (unit -> unit)
1052 val get_formatter_output_functions : unit -> (string -> int -> int ->
1057 unit) * (unit -> unit)
1058 Return the current output functions of the standard pretty-printer.
1060 Redefining formatter output
1065 The Format module is versatile enough to let you completely redefine
1066 the meaning of pretty-printing output: you may provide your own func‐
1067 tions to define how to handle indentation, line splitting, and even
1068 printing of all the characters that have to be printed!
1069 Redefining output functions
1071 type formatter_out_functions = {
1072 out_string : string -> int -> int -> unit ;
1073 out_flush : unit -> unit ;
1074 out_newline : unit -> unit ;
1075 out_spaces : int -> unit ;
1076 out_indent : int -> unit ;
1077 }
1078 The set of output functions specific to a formatter:
1081 -the out_string function performs all the pretty-printer string output.
1083 It is called with a string s , a start position p , and a number of
1084 characters n ; it is supposed to output characters p to p + n - 1 of s
1085 .
1086 -the out_flush function flushes the pretty-printer output device.
1088 - out_newline is called to open a new line when the pretty-printer
1090 splits the line.
1091 -the out_spaces function outputs spaces when a break hint leads to spa‐
1093 ces instead of a line split. It is called with the number of spaces to
1094 output.
1095 -the out_indent function performs new line indentation when the
1097 pretty-printer splits the line. It is called with the indentation value
1098 of the new line.
1099 By default:
1101 -fields out_string and out_flush are output device specific; (e.g.
1103 output_string and flush for a out_channel device, or Buffer.add_sub‐
1104 string and ignore for a Buffer.t output device),
1105 -field out_newline is equivalent to out_string \n 0 1 ;
1107 -fields out_spaces and out_indent are equivalent to out_string
1109 (String.make n ' ') 0 n .
1110 Since 4.01.0
1114 val pp_set_formatter_out_functions : formatter -> formatter_out_func‐
1118 tions -> unit
1119 val set_formatter_out_functions : formatter_out_functions -> unit
1124 pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer
1127 output functions of ppf to those of argument out_funs ,
1128 This way, you can change the meaning of indentation (which can be some‐
1130 thing else than just printing space characters) and the meaning of new
1131 lines opening (which can be connected to any other action needed by the
1132 application at hand).
1133 Reasonable defaults for functions out_spaces and out_newline are
1135 respectively out_funs.out_string (String.make n ' ') 0 n and
1136 out_funs.out_string \n 0 1 .
1137 Since 4.01.0
1140 val pp_get_formatter_out_functions : formatter -> unit -> format‐
1144 ter_out_functions
1145 val get_formatter_out_functions : unit -> formatter_out_functions
1150 Return the current output functions of the pretty-printer, including
1152 line splitting and indentation functions. Useful to record the current
1153 setting and restore it afterwards.
1154 Since 4.01.0
1157 Redefining semantic tag operations
1162 type formatter_stag_functions = {
1163 mark_open_stag : stag -> string ;
1164 mark_close_stag : stag -> string ;
1165 print_open_stag : stag -> unit ;
1166 print_close_stag : stag -> unit ;
1167 }
1168 The semantic tag handling functions specific to a formatter: mark ver‐
1171 sions are the 'tag-marking' functions that associate a string marker to
1172 a tag in order for the pretty-printing engine to write those markers as
1173 0 length tokens in the output device of the formatter. print versions
1174 are the 'tag-printing' functions that can perform regular printing when
1175 a tag is closed or opened.
1176 val pp_set_formatter_stag_functions : formatter -> formatter_stag_func‐
1180 tions -> unit
1181 val set_formatter_stag_functions : formatter_stag_functions -> unit
1186 pp_set_formatter_stag_functions ppf tag_funs changes the meaning of
1189 opening and closing semantic tag operations to use the functions in
1190 tag_funs when printing on ppf .
1191 When opening a semantic tag with name t , the string t is passed to the
1193 opening tag-marking function (the mark_open_stag field of the record
1194 tag_funs ), that must return the opening tag marker for that name. When
1195 the next call to close_stag () happens, the semantic tag name t is sent
1196 back to the closing tag-marking function (the mark_close_stag field of
1197 record tag_funs ), that must return a closing tag marker for that name.
1198 The print_ field of the record contains the tag-printing functions that
1200 are called at tag opening and tag closing time, to output regular mate‐
1201 rial in the pretty-printer queue.
1202 val pp_get_formatter_stag_functions : formatter -> unit -> format‐
1206 ter_stag_functions
1207 val get_formatter_stag_functions : unit -> formatter_stag_functions
1212 Return the current semantic tag operation functions of the standard
1214 pretty-printer.
1215 Defining formatters
1220 Defining new formatters permits unrelated output of material in paral‐
1221 lel on several output devices. All the parameters of a formatter are
1222 local to the formatter: right margin, maximum indentation limit, maxi‐
1223 mum number of pretty-printing boxes simultaneously open, ellipsis, and
1224 so on, are specific to each formatter and may be fixed independently.
1225 For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b
1227 returns a new formatter using buffer b as its output device. Simi‐
1228 larly, given a out_channel output channel oc , Format.format‐
1229 ter_of_out_channel oc returns a new formatter using channel oc as its
1230 output device.
1231 Alternatively, given out_funs , a complete set of output functions for
1233 a formatter, then Format.formatter_of_out_functions out_funs computes a
1234 new formatter using those functions for output.
1235 val formatter_of_out_channel : out_channel -> formatter
1237 formatter_of_out_channel oc returns a new formatter writing to the cor‐
1240 responding output channel oc .
1241 val std_formatter : formatter
1245 The standard formatter to write to standard output.
1247 It is defined as Format.formatter_of_out_channel stdout .
1249 val err_formatter : formatter
1253 A formatter to write to standard error.
1255 It is defined as Format.formatter_of_out_channel stderr .
1257 val formatter_of_buffer : Buffer.t -> formatter
1261 formatter_of_buffer b returns a new formatter writing to buffer b . At
1264 the end of pretty-printing, the formatter must be flushed using For‐
1265 mat.pp_print_flush or Format.pp_print_newline , to print all the pend‐
1266 ing material into the buffer.
1267 val stdbuf : Buffer.t
1271 The string buffer in which str_formatter writes.
1273 val str_formatter : formatter
1277 A formatter to output to the Format.stdbuf string buffer.
1279 str_formatter is defined as Format.formatter_of_buffer Format.stdbuf .
1282 val flush_str_formatter : unit -> string
1286 Returns the material printed with str_formatter , flushes the formatter
1288 and resets the corresponding buffer.
1289 val make_formatter : (string -> int -> int -> unit) -> (unit -> unit)
1293 -> formatter
1294 make_formatter out flush returns a new formatter that outputs with
1297 function out , and flushes with function flush .
1298 For instance, make_formatter (Stdlib.output oc) (fun () -> Stdlib.flush
1300 oc) returns a formatter to the out_channel oc .
1301 val formatter_of_out_functions : formatter_out_functions -> formatter
1305 formatter_of_out_functions out_funs returns a new formatter that writes
1308 with the set of output functions out_funs .
1309 See definition of type Format.formatter_out_functions for the meaning
1311 of argument out_funs .
1312 Since 4.06.0
1315 Symbolic pretty-printing
1320 Symbolic pretty-printing is pretty-printing using a symbolic formatter,
1321 i.e. a formatter that outputs symbolic pretty-printing items.
1322 When using a symbolic formatter, all regular pretty-printing activities
1324 occur but output material is symbolic and stored in a buffer of output
1325 items. At the end of pretty-printing, flushing the output buffer
1326 allows post-processing of symbolic output before performing low level
1327 output operations.
1328 In practice, first define a symbolic output buffer b using:
1330 - let sob = make_symbolic_output_buffer () . Then define a symbolic
1332 formatter with:
1333 - let ppf = formatter_of_symbolic_output_buffer sob
1335 Use symbolic formatter ppf as usual, and retrieve symbolic items at end
1337 of pretty-printing by flushing symbolic output buffer sob with:
1338 - flush_symbolic_output_buffer sob .
1340 type symbolic_output_item =
1343 | Output_flush (* symbolic flush command
1344 *)
1345 | Output_newline (* symbolic newline command
1346 *)
1347 | Output_string of string
1348 (* Output_string s : symbolic output for string s
1349 *)
1351 | Output_spaces of int
1352 (* Output_spaces n : symbolic command to output n spaces
1353 *)
1354 | Output_indent of int
1355 (* Output_indent i : symbolic indentation of size i
1356 *)
1358 Items produced by symbolic pretty-printers
1361 Since 4.06.0
1364 type symbolic_output_buffer
1367 The output buffer of a symbolic pretty-printer.
1370 Since 4.06.0
1373 val make_symbolic_output_buffer : unit -> symbolic_output_buffer
1377 make_symbolic_output_buffer () returns a fresh buffer for symbolic out‐
1380 put.
1381 Since 4.06.0
1384 val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
1388 clear_symbolic_output_buffer sob resets buffer sob .
1391 Since 4.06.0
1394 val get_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1398 bolic_output_item list
1399 get_symbolic_output_buffer sob returns the contents of buffer sob .
1402 Since 4.06.0
1405 val flush_symbolic_output_buffer : symbolic_output_buffer -> sym‐
1409 bolic_output_item list
1410 flush_symbolic_output_buffer sob returns the contents of buffer sob and
1413 resets buffer sob . flush_symbolic_output_buffer sob is equivalent to
1414 let items = get_symbolic_output_buffer sob in clear_symbolic_out‐
1415 put_buffer sob; items
1416 Since 4.06.0
1420 val add_symbolic_output_item : symbolic_output_buffer -> symbolic_out‐
1424 put_item -> unit
1425 add_symbolic_output_item sob itm adds item itm to buffer sob .
1428 Since 4.06.0
1431 val formatter_of_symbolic_output_buffer : symbolic_output_buffer ->
1435 formatter
1436 formatter_of_symbolic_output_buffer sob returns a symbolic formatter
1439 that outputs to symbolic_output_buffer sob .
1440 Since 4.06.0
1443 Convenience formatting functions.
1448 val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter
1449 -> 'a -> unit) -> formatter -> 'a list -> unit
1450 pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to
1453 print each item, and calling pp_sep between items ( pp_sep defaults to
1454 Format.pp_print_cut . Does nothing on empty lists.
1455 Since 4.02.0
1458 val pp_print_text : formatter -> string -> unit
1462 pp_print_text ppf s prints s with spaces and newlines respectively
1465 printed using Format.pp_print_space and Format.pp_force_newline .
1466 Since 4.02.0
1469 val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter
1473 -> 'a -> unit) -> formatter -> 'a option -> unit
1474 pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is
1477 Some v and none if it is None . none prints nothing by default.
1478 Since 4.08
1481 val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter
1485 -> 'e -> unit) -> formatter -> ('a, 'e) result -> unit
1486 pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _
1489 and error if r is Error _ .
1490 Since 4.08
1493 Formatted pretty-printing
1498 Module Format provides a complete set of printf like functions for
1499 pretty-printing using format string specifications.
1500 Specific annotations may be added in the format strings to give
1502 pretty-printing commands to the pretty-printing engine.
1503 Those annotations are introduced in the format strings using the @
1505 character. For instance, @ means a space break, @, means a cut, @[
1506 opens a new box, and @] closes the last open box.
1507 val fprintf : formatter -> ('a, formatter, unit) format -> 'a
1509 fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN accord‐
1515 ing to the format string fmt , and outputs the resulting string on the
1516 formatter ff .
1517 The format string fmt is a character string which contains three types
1519 of objects: plain characters and conversion specifications as specified
1520 in the Printf module, and pretty-printing indications specific to the
1521 Format module.
1522 The pretty-printing indication characters are introduced by a @ charac‐
1524 ter, and their meanings are:
1525 - @[ : open a pretty-printing box. The type and offset of the box may
1527 be optionally specified with the following syntax: the < character,
1528 followed by an optional box type indication, then an optional integer
1529 offset, and the closing > character. Pretty-printing box type is one
1530 of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
1531 pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box,
1532 ' hv ' stands for an 'horizontal/vertical' pretty-printing box, ' b '
1533 stands for an 'horizontal-or-vertical' pretty-printing box demonstrat‐
1534 ing indentation, ' hov ' stands a simple 'horizontal-or-vertical'
1535 pretty-printing box. For instance, @[<hov 2> opens an 'horizon‐
1536 tal-or-vertical' pretty-printing box with indentation 2 as obtained
1537 with open_hovbox 2 . For more details about pretty-printing boxes, see
1538 the various box opening functions open_*box .
1539 - @] : close the most recently opened pretty-printing box.
1541 - @, : output a 'cut' break hint, as with print_cut () .
1543 - @ : output a 'space' break hint, as with print_space () .
1545 - @; : output a 'full' break hint as with print_break . The nspaces and
1547 offset parameters of the break hint may be optionally specified with
1548 the following syntax: the < character, followed by an integer nspaces
1549 value, then an integer offset , and a closing > character. If no
1550 parameters are provided, the good break defaults to a 'space' break
1551 hint.
1552 - @. : flush the pretty-printer and split the line, as with print_new‐
1554 line () .
1555 - @<n> : print the following item as if it were of length n . Hence,
1557 printf @<0>%s arg prints arg as a zero length string. If @<n> is not
1558 followed by a conversion specification, then the following character of
1559 the format is printed as if it were of length n .
1560 - @{ : open a semantic tag. The name of the tag may be optionally spec‐
1562 ified with the following syntax: the < character, followed by an
1563 optional string specification, and the closing > character. The string
1564 specification is any character string that does not contain the closing
1565 character '>' . If omitted, the tag name defaults to the empty string.
1566 For more details about semantic tags, see the functions For‐
1567 mat.open_stag and Format.close_stag .
1568 - @} : close the most recently opened semantic tag.
1570 - @? : flush the pretty-printer as with print_flush () . This is
1572 equivalent to the conversion %! .
1573 - @\n : force a newline, as with force_newline () , not the normal way
1575 of pretty-printing, you should prefer using break hints inside a verti‐
1576 cal pretty-printing box.
1577 Note: To prevent the interpretation of a @ character as a pretty-print‐
1579 ing indication, escape it with a % character. Old quotation mode @@ is
1580 deprecated since it is not compatible with formatted input interpreta‐
1581 tion of character '@' .
1582 Example: printf @[%s@ %d@]@. x = 1 is equivalent to open_box ();
1584 print_string x = ; print_space (); print_int 1; close_box ();
1585 print_newline () . It prints x = 1 within a pretty-printing 'horizon‐
1586 tal-or-vertical' box.
1587 val printf : ('a, formatter, unit) format -> 'a
1589 Same as fprintf above, but output on std_formatter .
1591 val eprintf : ('a, formatter, unit) format -> 'a
1595 Same as fprintf above, but output on err_formatter .
1597 val sprintf : ('a, unit, string) format -> 'a
1601 Same as printf above, but instead of printing on a formatter, returns a
1603 string containing the result of formatting the arguments. Note that
1604 the pretty-printer queue is flushed at the end of each call to sprintf
1605 .
1606 In case of multiple and related calls to sprintf to output material on
1608 a single string, you should consider using fprintf with the predefined
1609 formatter str_formatter and call flush_str_formatter () to get the
1610 final result.
1611 Alternatively, you can use Format.fprintf with a formatter writing to a
1613 buffer of your own: flushing the formatter and the buffer at the end of
1614 pretty-printing returns the desired string.
1615 val asprintf : ('a, formatter, unit, string) format4 -> 'a
1619 Same as printf above, but instead of printing on a formatter, returns a
1621 string containing the result of formatting the arguments. The type of
1622 asprintf is general enough to interact nicely with %a conversions.
1623 Since 4.01.0
1626 val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
1630 Same as Format.fprintf , except the formatter is the last argument.
1632 dprintf ... a b c is a function of type formatter -> unit which can be
1633 given to a format specifier %t .
1634 This can be used as a replacement for Format.asprintf to delay format‐
1636 ting decisions. Using the string returned by Format.asprintf in a for‐
1637 matting context forces formatting decisions to be taken in isolation,
1638 and the final string may be created prematurely. Format.dprintf allows
1639 delay of formatting decisions until the final formatting context is
1640 known. For example: let t = Format.dprintf %i@ %i@ %i 1 2 3 in ...
1641 Format.printf @[<v>%t@] t
1642 Since 4.08.0
1646 val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
1650 Same as fprintf above, but does not print anything. Useful to ignore
1652 some material when conditionally printing.
1653 Since 3.10.0
1656 Formatted Pretty-Printing with continuations.
1661 val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1663 'a) format4 -> 'b
1664 Same as fprintf above, but instead of returning immediately, passes the
1666 formatter to its first argument at the end of printing.
1667 val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a)
1671 format4 -> 'b
1672 Same as Format.dprintf above, but instead of returning immediately,
1674 passes the suspended printer to its first argument at the end of print‐
1675 ing.
1676 Since 4.08.0
1679 val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
1683 'a) format4 -> 'b
1684 Same as kfprintf above, but does not print anything. Useful to ignore
1686 some material when conditionally printing.
1687 Since 3.12.0
1690 val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1694 Same as sprintf above, but instead of returning the string, passes it
1696 to the first argument.
1697 val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 ->
1701 'b
1702 Same as asprintf above, but instead of returning the string, passes it
1704 to the first argument.
1705 Since 4.03
1708 Deprecated
1713 val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
1714 Deprecated. This function is error prone. Do not use it. This func‐
1716 tion is neither compositional nor incremental, since it flushes the
1717 pretty-printer queue at each call.
1718 If you need to print to some buffer b , you must first define a format‐
1720 ter writing to b , using let to_b = formatter_of_buffer b ; then use
1721 regular calls to Format.fprintf with formatter to_b .
1722 val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
1726 Deprecated. An alias for ksprintf .
1728 val set_all_formatter_output_functions : out:(string -> int -> int ->
1732 unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int
1733 -> unit) -> unit
1734 Deprecated. Subsumed by set_formatter_out_functions .
1736 val get_all_formatter_output_functions : unit -> (string -> int -> int
1740 -> unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
1741 Deprecated. Subsumed by get_formatter_out_functions .
1743 val pp_set_all_formatter_output_functions : formatter -> out:(string ->
1747 int -> int -> unit) -> flush:(unit -> unit) -> newline:(unit -> unit)
1748 -> spaces:(int -> unit) -> unit
1749 Deprecated. Subsumed by pp_set_formatter_out_functions .
1751 val pp_get_all_formatter_output_functions : formatter -> unit ->
1755 (string -> int -> int -> unit) * (unit -> unit) * (unit -> unit) * (int
1756 -> unit)
1757 Deprecated. Subsumed by pp_get_formatter_out_functions .
1759 String tags
1764 val pp_open_tag : formatter -> tag -> unit
1765 Deprecated. Subsumed by Format.pp_open_stag .
1767 val open_tag : tag -> unit
1771 Deprecated. Subsumed by Format.open_stag .
1773 val pp_close_tag : formatter -> unit -> unit
1777 Deprecated. Subsumed by Format.pp_close_stag .
1779 val close_tag : unit -> unit
1783 Deprecated. Subsumed by Format.close_stag .
1785 type formatter_tag_functions = {
1788 mark_open_tag : tag -> string ;
1789 mark_close_tag : tag -> string ;
1790 print_open_tag : tag -> unit ;
1791 print_close_tag : tag -> unit ;
1792 }
1793 Deprecated. Subsumed by Format.formatter_stag_functions .
1796 val pp_set_formatter_tag_functions : formatter -> formatter_tag_func‐
1800 tions -> unit
1801 Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
1803 This function will erase non-string tag formatting functions.
1806 val set_formatter_tag_functions : formatter_tag_functions -> unit
1810 Deprecated. Subsumed by Format.set_formatter_stag_functions .
1812 val pp_get_formatter_tag_functions : formatter -> unit -> format‐
1816 ter_tag_functions
1817 Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
1819 val get_formatter_tag_functions : unit -> formatter_tag_functions
1823 Deprecated. Subsumed by Format.get_formatter_stag_functions .
1825OCamldoc 2019-07-30 Stdlib.Format(3)