Stdlib.Format(3o) OCaml library Stdlib.Format(3o)
NAME
Stdlib.Format - no description
Module
Module Stdlib.Format
Documentation
Module Format
: (module Stdlib__Format)
Introduction
You may consider this module as providing an extension to the printf
facility to provide automatic line splitting. The addition of
pretty-printing annotations to your regular printf format strings gives
you fancy indentation and line breaks. Pretty-printing annotations are
described below in the documentation of the function Format.fprintf .
You may also use the explicit pretty-printing box management and print-
ing functions provided by this module. This style is more basic but
more verbose than the concise fprintf format strings.
For instance, the sequence open_box 0; print_string "x ="; print_space
();
print_int 1; close_box (); print_newline () that prints x = 1
within a pretty-printing box, can be abbreviated as printf "@[%s@
%i@]@." "x =" 1 , or even shorter printf "@[x =@ %i@]@." 1 .
Rule of thumb for casual users of this library:
-use simple pretty-printing boxes (as obtained by open_box 0 );
-use simple break hints as obtained by print_cut () that outputs a sim-
ple break hint, or by print_space () that outputs a space indicating a
break hint;
-once a pretty-printing box is open, display its material with basic
printing functions (e. g. print_int and print_string );
-when the material for a pretty-printing box has been printed, call
close_box () to close the box;
-at the end of pretty-printing, flush the pretty-printer to display all
the remaining material, e.g. evaluate print_newline () .
The behavior of pretty-printing commands is unspecified if there is no
open pretty-printing box. Each box opened by one of the open_ functions
below must be closed using close_box for proper formatting. Otherwise,
some of the material printed in the boxes may not be output, or may be
formatted incorrectly.
In case of interactive use, each phrase is executed in the initial
state of the standard pretty-printer: after each phrase execution, the
interactive system closes all open pretty-printing boxes, flushes all
pending text, and resets the standard pretty-printer.
Warning: mixing calls to pretty-printing functions of this module with
calls to Stdlib low level output functions is error prone.
The pretty-printing functions output material that is delayed in the
pretty-printer queue and stacks in order to compute proper line split-
ting. In contrast, basic I/O output functions write directly in their
output device. As a consequence, the output of a basic I/O function may
appear before the output of a pretty-printing function that has been
called before. For instance,
Stdlib.print_string "<";
Format.print_string "PRETTY";
Stdlib.print_string ">";
Format.print_string "TEXT";
leads to output <>PRETTYTEXT .
Formatters
type formatter
Abstract data corresponding to a pretty-printer (also called a format-
ter) and all its machinery. See also Format.formatter .
Pretty-printing boxes
The pretty-printing engine uses the concepts of pretty-printing box and
break hint to drive indentation and line splitting behavior of the
pretty-printer.
Each different pretty-printing box kind introduces a specific line
splitting policy:
-within an horizontal box, break hints never split the line (but the
line may be split in a box nested deeper),
-within a vertical box, break hints always split the line,
-within an horizontal/vertical box, if the box fits on the current line
then break hints never split the line, otherwise break hint always
split the line,
-within a compacting box, a break hint never splits the line, unless
there is no more room on the current line.
Note that line splitting policy is box specific: the policy of a box
does not rule the policy of inner boxes. For instance, if a vertical
box is nested in an horizontal box, all break hints within the vertical
box will split the line.
Moreover, opening a box after the Format.maxindent splits the line
whether or not the box would end up fitting on the line.
val pp_open_box : formatter -> int -> unit
val open_box : int -> unit
pp_open_box ppf d opens a new compacting pretty-printing box with off-
set d in the formatter ppf .
Within this box, the pretty-printer prints as much as possible material
on every line.
A break hint splits the line if there is no more room on the line to
print the remainder of the box.
Within this box, the pretty-printer emphasizes the box structure: if a
structural box does not fit fully on a simple line, a break hint also
splits the line if the splitting ``moves to the left'' (i.e. the new
line gets an indentation smaller than the one of the current line).
This box is the general purpose pretty-printing box.
If the pretty-printer splits the line in the box, offset d is added to
the current indentation.
val pp_close_box : formatter -> unit -> unit
val close_box : unit -> unit
Closes the most recently open pretty-printing box.
val pp_open_hbox : formatter -> unit -> unit
val open_hbox : unit -> unit
pp_open_hbox ppf () opens a new 'horizontal' pretty-printing box.
This box prints material on a single line.
Break hints in a horizontal box never split the line. (Line splitting
may still occur inside boxes nested deeper).
val pp_open_vbox : formatter -> int -> unit
val open_vbox : int -> unit
pp_open_vbox ppf d opens a new 'vertical' pretty-printing box with off-
set d .
This box prints material on as many lines as break hints in the box.
Every break hint in a vertical box splits the line.
If the pretty-printer splits the line in the box, d is added to the
current indentation.
val pp_open_hvbox : formatter -> int -> unit
val open_hvbox : int -> unit
pp_open_hvbox ppf d opens a new 'horizontal/vertical' pretty-printing
box with offset d .
This box behaves as an horizontal box if it fits on a single line, oth-
erwise it behaves as a vertical box.
If the pretty-printer splits the line in the box, d is added to the
current indentation.
val pp_open_hovbox : formatter -> int -> unit
val open_hovbox : int -> unit
pp_open_hovbox ppf d opens a new 'horizontal-or-vertical' pretty-print-
ing box with offset d .
This box prints material as much as possible on every line.
A break hint splits the line if there is no more room on the line to
print the remainder of the box.
If the pretty-printer splits the line in the box, d is added to the
current indentation.
Formatting functions
val pp_print_string : formatter -> string -> unit
val print_string : string -> unit
pp_print_string ppf s prints s in the current pretty-printing box.
val pp_print_bytes : formatter -> bytes -> unit
val print_bytes : bytes -> unit
pp_print_bytes ppf b prints b in the current pretty-printing box.
Since 4.13.0
val pp_print_as : formatter -> int -> string -> unit
val print_as : int -> string -> unit
pp_print_as ppf len s prints s in the current pretty-printing box. The
pretty-printer formats s as if it were of length len .
val pp_print_int : formatter -> int -> unit
val print_int : int -> unit
Print an integer in the current pretty-printing box.
val pp_print_float : formatter -> float -> unit
val print_float : float -> unit
Print a floating point number in the current pretty-printing box.
val pp_print_char : formatter -> char -> unit
val print_char : char -> unit
Print a character in the current pretty-printing box.
val pp_print_bool : formatter -> bool -> unit
val print_bool : bool -> unit
Print a boolean in the current pretty-printing box.
Break hints
A 'break hint' tells the pretty-printer to output some space or split
the line whichever way is more appropriate to the current pretty-print-
ing box splitting rules.
Break hints are used to separate printing items and are mandatory to
let the pretty-printer correctly split lines and indent items.
Simple break hints are:
-the 'space': output a space or split the line if appropriate,
-the 'cut': split the line if appropriate.
Note: the notions of space and line splitting are abstract for the
pretty-printing engine, since those notions can be completely redefined
by the programmer. However, in the pretty-printer default setting,
``output a space'' simply means printing a space character (ASCII code
32) and ``split the line'' means printing a newline character (ASCII
code 10).
val pp_print_space : formatter -> unit -> unit
val print_space : unit -> unit
pp_print_space ppf () emits a 'space' break hint: the pretty-printer
may split the line at this point, otherwise it prints one space.
pp_print_space ppf () is equivalent to pp_print_break ppf 1 0 .
val pp_print_cut : formatter -> unit -> unit
val print_cut : unit -> unit
pp_print_cut ppf () emits a 'cut' break hint: the pretty-printer may
split the line at this point, otherwise it prints nothing.
pp_print_cut ppf () is equivalent to pp_print_break ppf 0 0 .
val pp_print_break : formatter -> int -> int -> unit
val print_break : int -> int -> unit
pp_print_break ppf nspaces offset emits a 'full' break hint: the
pretty-printer may split the line at this point, otherwise it prints
nspaces spaces.
If the pretty-printer splits the line, offset is added to the current
indentation.
val pp_print_custom_break : formatter -> fits:string * int * string ->
breaks:string * int * string -> unit
pp_print_custom_break ppf ~fits:(s1, n, s2) ~breaks:(s3, m, s4) emits a
custom break hint: the pretty-printer may split the line at this point.
If it does not split the line, then the s1 is emitted, then n spaces,
then s2 .
If it splits the line, then it emits the s3 string, then an indent (ac-
cording to the box rules), then an offset of m spaces, then the s4
string.
While n and m are handled by formatter_out_functions.out_indent , the
strings will be handled by formatter_out_functions.out_string . This
allows for a custom formatter that handles indentation distinctly, for
example, outputs <br/> tags or entities.
The custom break is useful if you want to change which visible
(non-whitespace) characters are printed in case of break or no break.
For example, when printing a list
[a; b; c]
trailing semicolon when it is printed vertically:
[
a;
b;
c;
]
You can do this as follows:
printf "@[<v 0>[@;<0 2>@[<v 0>a;@,b;@,c@]%t]@]@\n"
(pp_print_custom_break ~fits:("", 0, "") ~breaks:(";", 0, ""))
Since 4.08.0
val pp_force_newline : formatter -> unit -> unit
val force_newline : unit -> unit
Force a new line in the current pretty-printing box.
The pretty-printer must split the line at this point,
Not the normal way of pretty-printing, since imperative line splitting
may interfere with current line counters and box size calculation. Us-
ing break hints within an enclosing vertical box is a better alterna-
tive.
val pp_print_if_newline : formatter -> unit -> unit
val print_if_newline : unit -> unit
Execute the next formatting command if the preceding line has just been
split. Otherwise, ignore the next formatting command.
Pretty-printing termination
val pp_print_flush : formatter -> unit -> unit
val print_flush : unit -> unit
End of pretty-printing: resets the pretty-printer to initial state.
All open pretty-printing boxes are closed, all pending text is printed.
In addition, the pretty-printer low level output device is flushed to
ensure that all pending text is really displayed.
Note: never use print_flush in the normal course of a pretty-printing
routine, since the pretty-printer uses a complex buffering machinery to
properly indent the output; manually flushing those buffers at random
would conflict with the pretty-printer strategy and result to poor ren-
dering.
Only consider using print_flush when displaying all pending material is
mandatory (for instance in case of interactive use when you want the
user to read some text) and when resetting the pretty-printer state
will not disturb further pretty-printing.
Warning: If the output device of the pretty-printer is an output chan-
nel, repeated calls to print_flush means repeated calls to flush to
flush the out channel; these explicit flush calls could foil the
buffering strategy of output channels and could dramatically impact ef-
ficiency.
val pp_print_newline : formatter -> unit -> unit
val print_newline : unit -> unit
End of pretty-printing: resets the pretty-printer to initial state.
All open pretty-printing boxes are closed, all pending text is printed.
Equivalent to Format.print_flush followed by a new line. See corre-
sponding words of caution for Format.print_flush .
Note: this is not the normal way to output a new line; the preferred
method is using break hints within a vertical pretty-printing box.
Margin
val pp_set_margin : formatter -> int -> unit
val set_margin : int -> unit
pp_set_margin ppf d sets the right margin to d (in characters): the
pretty-printer splits lines that overflow the right margin according to
the break hints given. Setting the margin to d means that the format-
ting engine aims at printing at most d-1 characters per line. Nothing
happens if d is smaller than 2. If d is too large, the right margin is
set to the maximum admissible value (which is greater than 10 ^ 9 ).
If d is less than the current maximum indentation limit, the maximum
indentation limit is decreased while trying to preserve a minimal ratio
max_indent/margin>=50% and if possible the current difference margin -
max_indent .
See also Format.pp_set_geometry .
val pp_get_margin : formatter -> unit -> int
val get_margin : unit -> int
Returns the position of the right margin.
Maximum indentation limit
val pp_set_max_indent : formatter -> int -> unit
val set_max_indent : int -> unit
pp_set_max_indent ppf d sets the maximum indentation limit of lines to
d (in characters): once this limit is reached, new pretty-printing
boxes are rejected to the left, unless the enclosing box fully fits on
the current line. As an illustration,
set_margin 10; set_max_indent 5; printf "@[123456@[7@]89A@]@."
yields
123456
789A
because the nested box "@[7@]" is opened after the maximum indentation
limit ( 7>5 ) and its parent box does not fit on the current line. Ei-
ther decreasing the length of the parent box to make it fit on a line:
printf "@[123456@[7@]89@]@."
or opening an intermediary box before the maximum indentation limit
which fits on the current line
printf "@[123@[456@[7@]89@]A@]@."
avoids the rejection to the left of the inner boxes and print respec-
tively "123456789" and "123456789A" . Note also that vertical boxes
never fit on a line whereas horizontal boxes always fully fit on the
current line. Opening a box may split a line whereas the contents may
have fit. If this behavior is problematic, it can be curtailed by set-
ting the maximum indentation limit to margin - 1 . Note that setting
the maximum indentation limit to margin is invalid.
Nothing happens if d is smaller than 2.
If d is too large, the limit is set to the maximum admissible value
(which is greater than 10 ^ 9 ).
If d is greater or equal than the current margin, it is ignored, and
the current maximum indentation limit is kept.
See also Format.pp_set_geometry .
val pp_get_max_indent : formatter -> unit -> int
val get_max_indent : unit -> int
Return the maximum indentation limit (in characters).
Geometry
Geometric functions can be used to manipulate simultaneously the cou-
pled variables, margin and maxixum indentation limit.
type geometry = {
max_indent : int ;
margin : int ;
}
val check_geometry : geometry -> bool
Check if the formatter geometry is valid: 1 < max_indent < margin
val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
val set_geometry : max_indent:int -> margin:int -> unit
val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int ->
unit
val safe_set_geometry : max_indent:int -> margin:int -> unit
pp_set_geometry ppf ~max_indent ~margin sets both the margin and maxi-
mum indentation limit for ppf .
When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin
is equivalent to pp_set_margin ppf margin; pp_set_max_indent ppf
max_indent ; and avoids the subtly incorrect pp_set_max_indent ppf
max_indent; pp_set_margin ppf margin ;
Outside of this domain, pp_set_geometry raises an invalid argument ex-
ception whereas pp_safe_set_geometry does nothing.
Since 4.08.0
val pp_update_geometry : formatter -> (geometry -> geometry) -> unit
pp_update_geometry ppf (fun geo -> { geo with ... }) lets you update a
formatter's geometry in a way that is robust to extension of the geome-
try record with new fields.
Raises an invalid argument exception if the returned geometry does not
satisfy Format.check_geometry .
Since 4.11.0
val update_geometry : (geometry -> geometry) -> unit
val pp_get_geometry : formatter -> unit -> geometry
val get_geometry : unit -> geometry
Return the current geometry of the formatter
Since 4.08.0
Maximum formatting depth
The maximum formatting depth is the maximum number of pretty-printing
boxes simultaneously open.
Material inside boxes nested deeper is printed as an ellipsis (more
precisely as the text returned by Format.get_ellipsis_text () ).
val pp_set_max_boxes : formatter -> int -> unit
val set_max_boxes : int -> unit
pp_set_max_boxes ppf max sets the maximum number of pretty-printing
boxes simultaneously open.
Material inside boxes nested deeper is printed as an ellipsis (more
precisely as the text returned by Format.get_ellipsis_text () ).
Nothing happens if max is smaller than 2.
val pp_get_max_boxes : formatter -> unit -> int
val get_max_boxes : unit -> int
Returns the maximum number of pretty-printing boxes allowed before el-
lipsis.
val pp_over_max_boxes : formatter -> unit -> bool
val over_max_boxes : unit -> bool
Tests if the maximum number of pretty-printing boxes allowed have al-
ready been opened.
Tabulation boxes
A tabulation box prints material on lines divided into cells of fixed
length. A tabulation box provides a simple way to display vertical col-
umns of left adjusted text.
This box features command set_tab to define cell boundaries, and com-
mand print_tab to move from cell to cell and split the line when there
is no more cells to print on the line.
Note: printing within tabulation box is line directed, so arbitrary
line splitting inside a tabulation box leads to poor rendering. Yet,
controlled use of tabulation boxes allows simple printing of columns
within module Format .
val pp_open_tbox : formatter -> unit -> unit
val open_tbox : unit -> unit
open_tbox () opens a new tabulation box.
This box prints lines separated into cells of fixed width.
Inside a tabulation box, special tabulation markers defines points of
interest on the line (for instance to delimit cell boundaries). Func-
tion Format.set_tab sets a tabulation marker at insertion point.
A tabulation box features specific tabulation breaks to move to next
tabulation marker or split the line. Function Format.print_tbreak
prints a tabulation break.
val pp_close_tbox : formatter -> unit -> unit
val close_tbox : unit -> unit
Closes the most recently opened tabulation box.
val pp_set_tab : formatter -> unit -> unit
val set_tab : unit -> unit
Sets a tabulation marker at current insertion point.
val pp_print_tab : formatter -> unit -> unit
val print_tab : unit -> unit
print_tab () emits a 'next' tabulation break hint: if not already set
on a tabulation marker, the insertion point moves to the first tabula-
tion marker on the right, or the pretty-printer splits the line and in-
sertion point moves to the leftmost tabulation marker.
It is equivalent to print_tbreak 0 0 .
val pp_print_tbreak : formatter -> int -> int -> unit
val print_tbreak : int -> int -> unit
print_tbreak nspaces offset emits a 'full' tabulation break hint.
If not already set on a tabulation marker, the insertion point moves to
the first tabulation marker on the right and the pretty-printer prints
nspaces spaces.
If there is no next tabulation marker on the right, the pretty-printer
splits the line at this point, then insertion point moves to the left-
most tabulation marker of the box.
If the pretty-printer splits the line, offset is added to the current
indentation.
Ellipsis
val pp_set_ellipsis_text : formatter -> string -> unit
val set_ellipsis_text : string -> unit
Set the text of the ellipsis printed when too many pretty-printing
boxes are open (a single dot, . , by default).
val pp_get_ellipsis_text : formatter -> unit -> string
val get_ellipsis_text : unit -> string
Return the text of the ellipsis.
Semantic tags
type stag = ..
Semantic tags (or simply tags) are user's defined annotations to asso-
ciate user's specific operations to printed entities.
Common usage of semantic tags is text decoration to get specific font
or text size rendering for a display device, or marking delimitation of
entities (e.g. HTML or TeX elements or terminal escape sequences).
More sophisticated usage of semantic tags could handle dynamic modifi-
cation of the pretty-printer behavior to properly print the material
within some specific tags. For instance, we can define an RGB tag like
so:
type stag += RGB of {r:int;g:int;b:int}
In order to properly delimit printed entities, a semantic tag must be
opened before and closed after the entity. Semantic tags must be prop-
erly nested like parentheses using Format.pp_open_stag and For-
mat.pp_close_stag .
Tag specific operations occur any time a tag is opened or closed, At
each occurrence, two kinds of operations are performed tag-marking and
tag-printing:
-The tag-marking operation is the simpler tag specific operation: it
simply writes a tag specific string into the output device of the for-
matter. Tag-marking does not interfere with line-splitting computation.
-The tag-printing operation is the more involved tag specific opera-
tion: it can print arbitrary material to the formatter. Tag-printing is
tightly linked to the current pretty-printer operations.
Roughly speaking, tag-marking is commonly used to get a better render-
ing of texts in the rendering device, while tag-printing allows fine
tuning of printing routines to print the same entity differently ac-
cording to the semantic tags (i.e. print additional material or even
omit parts of the output).
More precisely: when a semantic tag is opened or closed then both and
successive 'tag-printing' and 'tag-marking' operations occur:
-Tag-printing a semantic tag means calling the formatter specific func-
tion print_open_stag (resp. print_close_stag ) with the name of the
tag as argument: that tag-printing function can then print any regular
material to the formatter (so that this material is enqueued as usual
in the formatter queue for further line splitting computation).
-Tag-marking a semantic tag means calling the formatter specific func-
tion mark_open_stag (resp. mark_close_stag ) with the name of the tag
as argument: that tag-marking function can then return the 'tag-opening
marker' (resp. `tag-closing marker') for direct output into the output
device of the formatter.
Being written directly into the output device of the formatter, seman-
tic tag marker strings are not considered as part of the printing mate-
rial that drives line splitting (in other words, the length of the
strings corresponding to tag markers is considered as zero for line
splitting).
Thus, semantic tag handling is in some sense transparent to
pretty-printing and does not interfere with usual indentation. Hence, a
single pretty-printing routine can output both simple 'verbatim' mate-
rial or richer decorated output depending on the treatment of tags. By
default, tags are not active, hence the output is not decorated with
tag information. Once set_tags is set to true , the pretty-printer en-
gine honors tags and decorates the output accordingly.
Default tag-marking functions behave the HTML way: Format.tag are en-
closed in "<" and ">" while other tags are ignored; hence, opening
marker for tag string "t" is "<t>" and closing marker is "</t>" .
Default tag-printing functions just do nothing.
Tag-marking and tag-printing functions are user definable and can be
set by calling Format.set_formatter_stag_functions .
Semantic tag operations may be set on or off with Format.set_tags .
Tag-marking operations may be set on or off with Format.set_mark_tags .
Tag-printing operations may be set on or off with Format.set_print_tags
.
Since 4.08.0
type tag = string
type Format.stag +=
| String_tag of tag (* String_tag s is a string tag s . String tags
can be inserted either by explicitly using the constructor String_tag
or by using the dedicated format syntax "@{<s> ... @}" .
Since 4.08.0
*)
val pp_open_stag : formatter -> stag -> unit
val open_stag : stag -> unit
pp_open_stag ppf t opens the semantic tag named t .
The print_open_stag tag-printing function of the formatter is called
with t as argument; then the opening tag marker for t , as given by
mark_open_stag t , is written into the output device of the formatter.
Since 4.08.0
val pp_close_stag : formatter -> unit -> unit
val close_stag : unit -> unit
pp_close_stag ppf () closes the most recently opened semantic tag t .
The closing tag marker, as given by mark_close_stag t , is written into
the output device of the formatter; then the print_close_stag
tag-printing function of the formatter is called with t as argument.
Since 4.08.0
val pp_set_tags : formatter -> bool -> unit
val set_tags : bool -> unit
pp_set_tags ppf b turns on or off the treatment of semantic tags (de-
fault is off).
val pp_set_print_tags : formatter -> bool -> unit
val set_print_tags : bool -> unit
pp_set_print_tags ppf b turns on or off the tag-printing operations.
val pp_set_mark_tags : formatter -> bool -> unit
val set_mark_tags : bool -> unit
pp_set_mark_tags ppf b turns on or off the tag-marking operations.
val pp_get_print_tags : formatter -> unit -> bool
val get_print_tags : unit -> bool
Return the current status of tag-printing operations.
val pp_get_mark_tags : formatter -> unit -> bool
val get_mark_tags : unit -> bool
Return the current status of tag-marking operations.
val pp_set_formatter_out_channel : formatter -> out_channel -> unit
Redirecting the standard formatter output
val set_formatter_out_channel : out_channel -> unit
Redirect the standard pretty-printer output to the given channel. (All
the output functions of the standard formatter are set to the default
output functions printing to the given channel.)
set_formatter_out_channel is equivalent to Format.pp_set_format-
ter_out_channel std_formatter .
val pp_set_formatter_output_functions : formatter -> (string -> int ->
int -> unit) -> (unit -> unit) -> unit
val set_formatter_output_functions : (string -> int -> int -> unit) ->
(unit -> unit) -> unit
pp_set_formatter_output_functions ppf out flush redirects the standard
pretty-printer output functions to the functions out and flush .
The out function performs all the pretty-printer string output. It is
called with a string s , a start position p , and a number of charac-
ters n ; it is supposed to output characters p to p + n - 1 of s .
The flush function is called whenever the pretty-printer is flushed
(via conversion %! , or pretty-printing indications @? or @. , or
using low level functions print_flush or print_newline ).
val pp_get_formatter_output_functions : formatter -> unit -> (string ->
int -> int -> unit) * (unit -> unit)
val get_formatter_output_functions : unit -> (string -> int -> int ->
unit) * (unit -> unit)
Return the current output functions of the standard pretty-printer.
Redefining formatter output
The Format module is versatile enough to let you completely redefine
the meaning of pretty-printing output: you may provide your own func-
tions to define how to handle indentation, line splitting, and even
printing of all the characters that have to be printed!
Redefining output functions
type formatter_out_functions = {
out_string : string -> int -> int -> unit ;
out_flush : unit -> unit ;
out_newline : unit -> unit ;
out_spaces : int -> unit ;
out_indent : int -> unit ; (* .B "Since" 4.06.0
*)
}
The set of output functions specific to a formatter:
-the out_string function performs all the pretty-printer string output.
It is called with a string s , a start position p , and a number of
characters n ; it is supposed to output characters p to p + n - 1 of s
.
-the out_flush function flushes the pretty-printer output device.
- out_newline is called to open a new line when the pretty-printer
splits the line.
-the out_spaces function outputs spaces when a break hint leads to spa-
ces instead of a line split. It is called with the number of spaces to
output.
-the out_indent function performs new line indentation when the
pretty-printer splits the line. It is called with the indentation value
of the new line.
By default:
-fields out_string and out_flush are output device specific; (e.g.
output_string and flush for a out_channel device, or Buffer.add_sub-
string and ignore for a Buffer.t output device),
-field out_newline is equivalent to out_string "\n" 0 1 ;
-fields out_spaces and out_indent are equivalent to out_string
(String.make n ' ') 0 n .
Since 4.01.0
val pp_set_formatter_out_functions : formatter -> formatter_out_func-
tions -> unit
val set_formatter_out_functions : formatter_out_functions -> unit
pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer
output functions of ppf to those of argument out_funs ,
This way, you can change the meaning of indentation (which can be some-
thing else than just printing space characters) and the meaning of new
lines opening (which can be connected to any other action needed by the
application at hand).
Reasonable defaults for functions out_spaces and out_newline are re-
spectively out_funs.out_string (String.make n ' ') 0 n and
out_funs.out_string "\n" 0 1 .
Since 4.01.0
val pp_get_formatter_out_functions : formatter -> unit -> format-
ter_out_functions
val get_formatter_out_functions : unit -> formatter_out_functions
Return the current output functions of the pretty-printer, including
line splitting and indentation functions. Useful to record the current
setting and restore it afterwards.
Since 4.01.0
Redefining semantic tag operations
type formatter_stag_functions = {
mark_open_stag : stag -> string ;
mark_close_stag : stag -> string ;
print_open_stag : stag -> unit ;
print_close_stag : stag -> unit ;
}
The semantic tag handling functions specific to a formatter: mark ver-
sions are the 'tag-marking' functions that associate a string marker to
a tag in order for the pretty-printing engine to write those markers as
0 length tokens in the output device of the formatter. print versions
are the 'tag-printing' functions that can perform regular printing when
a tag is closed or opened.
Since 4.08.0
val pp_set_formatter_stag_functions : formatter -> formatter_stag_func-
tions -> unit
val set_formatter_stag_functions : formatter_stag_functions -> unit
pp_set_formatter_stag_functions ppf tag_funs changes the meaning of
opening and closing semantic tag operations to use the functions in
tag_funs when printing on ppf .
When opening a semantic tag with name t , the string t is passed to the
opening tag-marking function (the mark_open_stag field of the record
tag_funs ), that must return the opening tag marker for that name. When
the next call to close_stag () happens, the semantic tag name t is sent
back to the closing tag-marking function (the mark_close_stag field of
record tag_funs ), that must return a closing tag marker for that name.
The print_ field of the record contains the tag-printing functions that
are called at tag opening and tag closing time, to output regular mate-
rial in the pretty-printer queue.
Since 4.08.0
val pp_get_formatter_stag_functions : formatter -> unit -> format-
ter_stag_functions
val get_formatter_stag_functions : unit -> formatter_stag_functions
Return the current semantic tag operation functions of the standard
pretty-printer.
Since 4.08.0
Defining formatters
Defining new formatters permits unrelated output of material in paral-
lel on several output devices. All the parameters of a formatter are
local to the formatter: right margin, maximum indentation limit, maxi-
mum number of pretty-printing boxes simultaneously open, ellipsis, and
so on, are specific to each formatter and may be fixed independently.
For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b
returns a new formatter using buffer b as its output device. Simi-
larly, given a out_channel output channel oc , Format.format-
ter_of_out_channel oc returns a new formatter using channel oc as its
output device.
Alternatively, given out_funs , a complete set of output functions for
a formatter, then Format.formatter_of_out_functions out_funs computes a
new formatter using those functions for output.
val formatter_of_out_channel : out_channel -> formatter
formatter_of_out_channel oc returns a new formatter writing to the cor-
responding output channel oc .
val std_formatter : formatter
The standard formatter to write to standard output.
It is defined as Format.formatter_of_out_channel stdout .
val err_formatter : formatter
A formatter to write to standard error.
It is defined as Format.formatter_of_out_channel stderr .
val formatter_of_buffer : Buffer.t -> formatter
formatter_of_buffer b returns a new formatter writing to buffer b . At
the end of pretty-printing, the formatter must be flushed using For-
mat.pp_print_flush or Format.pp_print_newline , to print all the pend-
ing material into the buffer.
val stdbuf : Buffer.t
The string buffer in which str_formatter writes.
val str_formatter : formatter
A formatter to output to the Format.stdbuf string buffer.
str_formatter is defined as Format.formatter_of_buffer Format.stdbuf .
val flush_str_formatter : unit -> string
Returns the material printed with str_formatter , flushes the formatter
and resets the corresponding buffer.
val make_formatter : (string -> int -> int -> unit) -> (unit -> unit)
-> formatter
make_formatter out flush returns a new formatter that outputs with
function out , and flushes with function flush .
For instance,
make_formatter
(Stdlib.output oc)
(fun () -> Stdlib.flush oc)
returns a formatter to the out_channel oc .
val formatter_of_out_functions : formatter_out_functions -> formatter
formatter_of_out_functions out_funs returns a new formatter that writes
with the set of output functions out_funs .
See definition of type Format.formatter_out_functions for the meaning
of argument out_funs .
Since 4.06.0
Symbolic pretty-printing
Symbolic pretty-printing is pretty-printing using a symbolic formatter,
i.e. a formatter that outputs symbolic pretty-printing items.
When using a symbolic formatter, all regular pretty-printing activities
occur but output material is symbolic and stored in a buffer of output
items. At the end of pretty-printing, flushing the output buffer al-
lows post-processing of symbolic output before performing low level
output operations.
In practice, first define a symbolic output buffer b using:
- let sob = make_symbolic_output_buffer () . Then define a symbolic
formatter with:
- let ppf = formatter_of_symbolic_output_buffer sob
Use symbolic formatter ppf as usual, and retrieve symbolic items at end
of pretty-printing by flushing symbolic output buffer sob with:
- flush_symbolic_output_buffer sob .
type symbolic_output_item =
| Output_flush (* symbolic flush command
*)
| Output_newline (* symbolic newline command
*)
| Output_string of string
(* Output_string s : symbolic output for string s
*)
| Output_spaces of int
(* Output_spaces n : symbolic command to output n spaces
*)
| Output_indent of int
(* Output_indent i : symbolic indentation of size i
*)
Items produced by symbolic pretty-printers
Since 4.06.0
type symbolic_output_buffer
The output buffer of a symbolic pretty-printer.
Since 4.06.0
val make_symbolic_output_buffer : unit -> symbolic_output_buffer
make_symbolic_output_buffer () returns a fresh buffer for symbolic out-
put.
Since 4.06.0
val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
clear_symbolic_output_buffer sob resets buffer sob .
Since 4.06.0
val get_symbolic_output_buffer : symbolic_output_buffer -> sym-
bolic_output_item list
get_symbolic_output_buffer sob returns the contents of buffer sob .
Since 4.06.0
val flush_symbolic_output_buffer : symbolic_output_buffer -> sym-
bolic_output_item list
flush_symbolic_output_buffer sob returns the contents of buffer sob and
resets buffer sob . flush_symbolic_output_buffer sob is equivalent to
let items = get_symbolic_output_buffer sob in
clear_symbolic_output_buffer sob; items
Since 4.06.0
val add_symbolic_output_item : symbolic_output_buffer -> symbolic_out-
put_item -> unit
add_symbolic_output_item sob itm adds item itm to buffer sob .
Since 4.06.0
val formatter_of_symbolic_output_buffer : symbolic_output_buffer ->
formatter
formatter_of_symbolic_output_buffer sob returns a symbolic formatter
that outputs to symbolic_output_buffer sob .
Since 4.06.0
Convenience formatting functions.
val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter
-> 'a -> unit) -> formatter -> 'a list -> unit
pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to
print each item, and calling pp_sep between items ( pp_sep defaults to
Format.pp_print_cut . Does nothing on empty lists.
Since 4.02.0
val pp_print_seq : ?pp_sep:(formatter -> unit -> unit) -> (formatter ->
'a -> unit) -> formatter -> 'a Seq.t -> unit
pp_print_seq ?pp_sep pp_v ppf s prints items of sequence s , using pp_v
to print each item, and calling pp_sep between items ( pp_sep defaults
to Format.pp_print_cut . Does nothing on empty sequences.
This function does not terminate on infinite sequences.
Since 4.12
val pp_print_text : formatter -> string -> unit
pp_print_text ppf s prints s with spaces and newlines respectively
printed using Format.pp_print_space and Format.pp_force_newline .
Since 4.02.0
val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter
-> 'a -> unit) -> formatter -> 'a option -> unit
pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is
Some v and none if it is None . none prints nothing by default.
Since 4.08
val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter
-> 'e -> unit) -> formatter -> ('a, 'e) result -> unit
pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _
and error if r is Error _ .
Since 4.08
val pp_print_either : left:(formatter -> 'a -> unit) -> right:(format-
ter -> 'b -> unit) -> formatter -> ('a, 'b) Either.t -> unit
pp_print_either ~left ~right ppf e prints e on ppf using left if e is
Either.Left _ and right if e is Either.Right _ .
Since 4.13
Formatted pretty-printing
Module Format provides a complete set of printf like functions for
pretty-printing using format string specifications.
Specific annotations may be added in the format strings to give
pretty-printing commands to the pretty-printing engine.
Those annotations are introduced in the format strings using the @
character. For instance, @ means a space break, @, means a cut, @[
opens a new box, and @] closes the last open box.
val fprintf : formatter -> ('a, formatter, unit) format -> 'a
fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN accord-
ing to the format string fmt , and outputs the resulting string on the
formatter ff .
The format string fmt is a character string which contains three types
of objects: plain characters and conversion specifications as specified
in the Printf module, and pretty-printing indications specific to the
Format module.
The pretty-printing indication characters are introduced by a @ charac-
ter, and their meanings are:
- @[ : open a pretty-printing box. The type and offset of the box may
be optionally specified with the following syntax: the < character,
followed by an optional box type indication, then an optional integer
offset, and the closing > character. Pretty-printing box type is one
of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box,
' hv ' stands for an 'horizontal/vertical' pretty-printing box, ' b '
stands for an 'horizontal-or-vertical' pretty-printing box demonstrat-
ing indentation, ' hov ' stands a simple 'horizontal-or-vertical'
pretty-printing box. For instance, @[<hov 2> opens an 'horizon-
tal-or-vertical' pretty-printing box with indentation 2 as obtained
with open_hovbox 2 . For more details about pretty-printing boxes, see
the various box opening functions open_*box .
- @] : close the most recently opened pretty-printing box.
- @, : output a 'cut' break hint, as with print_cut () .
- @ : output a 'space' break hint, as with print_space () .
- @; : output a 'full' break hint as with print_break . The nspaces and
offset parameters of the break hint may be optionally specified with
the following syntax: the < character, followed by an integer nspaces
value, then an integer offset , and a closing > character. If no pa-
rameters are provided, the good break defaults to a 'space' break hint.
- @. : flush the pretty-printer and split the line, as with print_new-
line () .
- @<n> : print the following item as if it were of length n . Hence,
printf "@<0>%s" arg prints arg as a zero length string. If @<n> is not
followed by a conversion specification, then the following character of
the format is printed as if it were of length n .
- @{ : open a semantic tag. The name of the tag may be optionally spec-
ified with the following syntax: the < character, followed by an op-
tional string specification, and the closing > character. The string
specification is any character string that does not contain the closing
character '>' . If omitted, the tag name defaults to the empty string.
For more details about semantic tags, see the functions For-
mat.open_stag and Format.close_stag .
- @} : close the most recently opened semantic tag.
- @? : flush the pretty-printer as with print_flush () . This is
equivalent to the conversion %! .
- @\n : force a newline, as with force_newline () , not the normal way
of pretty-printing, you should prefer using break hints inside a verti-
cal pretty-printing box.
Note: To prevent the interpretation of a @ character as a pretty-print-
ing indication, escape it with a % character. Old quotation mode @@ is
deprecated since it is not compatible with formatted input interpreta-
tion of character '@' .
Example: printf "@[%s@ %d@]@." "x =" 1 is equivalent to open_box ();
print_string "x ="; print_space ();
print_int 1; close_box (); print_newline () . It prints x = 1
within a pretty-printing 'horizontal-or-vertical' box.
val printf : ('a, formatter, unit) format -> 'a
Same as fprintf above, but output on std_formatter .
val eprintf : ('a, formatter, unit) format -> 'a
Same as fprintf above, but output on err_formatter .
val sprintf : ('a, unit, string) format -> 'a
Same as printf above, but instead of printing on a formatter, returns a
string containing the result of formatting the arguments. Note that
the pretty-printer queue is flushed at the end of each call to sprintf
.
In case of multiple and related calls to sprintf to output material on
a single string, you should consider using fprintf with the predefined
formatter str_formatter and call flush_str_formatter () to get the fi-
nal result.
Alternatively, you can use Format.fprintf with a formatter writing to a
buffer of your own: flushing the formatter and the buffer at the end of
pretty-printing returns the desired string.
val asprintf : ('a, formatter, unit, string) format4 -> 'a
Same as printf above, but instead of printing on a formatter, returns a
string containing the result of formatting the arguments. The type of
asprintf is general enough to interact nicely with %a conversions.
Since 4.01.0
val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
Same as Format.fprintf , except the formatter is the last argument.
dprintf "..." a b c is a function of type formatter -> unit which can
be given to a format specifier %t .
This can be used as a replacement for Format.asprintf to delay format-
ting decisions. Using the string returned by Format.asprintf in a for-
matting context forces formatting decisions to be taken in isolation,
and the final string may be created prematurely. Format.dprintf allows
delay of formatting decisions until the final formatting context is
known. For example:
let t = Format.dprintf "%i@ %i@ %i" 1 2 3 in
...
Format.printf "@[<v>%t@]" t
Since 4.08.0
val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
Same as fprintf above, but does not print anything. Useful to ignore
some material when conditionally printing.
Since 3.10.0
Formatted Pretty-Printing with continuations.
val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
'a) format4 -> 'b
Same as fprintf above, but instead of returning immediately, passes the
formatter to its first argument at the end of printing.
val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a)
format4 -> 'b
Same as Format.dprintf above, but instead of returning immediately,
passes the suspended printer to its first argument at the end of print-
ing.
Since 4.08.0
val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit,
'a) format4 -> 'b
Same as kfprintf above, but does not print anything. Useful to ignore
some material when conditionally printing.
Since 3.12.0
val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
Same as sprintf above, but instead of returning the string, passes it
to the first argument.
val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 ->
'b
Same as asprintf above, but instead of returning the string, passes it
to the first argument.
Since 4.03
Deprecated
val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
Deprecated. This function is error prone. Do not use it. This func-
tion is neither compositional nor incremental, since it flushes the
pretty-printer queue at each call.
If you need to print to some buffer b , you must first define a format-
ter writing to b , using let to_b = formatter_of_buffer b ; then use
regular calls to Format.fprintf with formatter to_b .
val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
Deprecated. An alias for ksprintf .
val set_all_formatter_output_functions : out:(string -> int -> int ->
unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int
-> unit) -> unit
Deprecated. Subsumed by set_formatter_out_functions .
val get_all_formatter_output_functions : unit -> (string -> int -> int
-> unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
Deprecated. Subsumed by get_formatter_out_functions .
val pp_set_all_formatter_output_functions : formatter -> out:(string ->
int -> int -> unit) -> flush:(unit -> unit) -> newline:(unit -> unit)
-> spaces:(int -> unit) -> unit
Deprecated. Subsumed by pp_set_formatter_out_functions .
val pp_get_all_formatter_output_functions : formatter -> unit ->
(string -> int -> int -> unit) * (unit -> unit) * (unit -> unit) * (int
-> unit)
Deprecated. Subsumed by pp_get_formatter_out_functions .
String tags
val pp_open_tag : formatter -> tag -> unit
Deprecated. Subsumed by Format.pp_open_stag .
val open_tag : tag -> unit
Deprecated. Subsumed by Format.open_stag .
val pp_close_tag : formatter -> unit -> unit
Deprecated. Subsumed by Format.pp_close_stag .
val close_tag : unit -> unit
Deprecated. Subsumed by Format.close_stag .
type formatter_tag_functions = {
mark_open_tag : tag -> string ;
mark_close_tag : tag -> string ;
print_open_tag : tag -> unit ;
print_close_tag : tag -> unit ;
}
Deprecated. Subsumed by Format.formatter_stag_functions .
val pp_set_formatter_tag_functions : formatter -> formatter_tag_func-
tions -> unit
Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
This function will erase non-string tag formatting functions.
val set_formatter_tag_functions : formatter_tag_functions -> unit
Deprecated. Subsumed by Format.set_formatter_stag_functions .
val pp_get_formatter_tag_functions : formatter -> unit -> format-
ter_tag_functions
Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
val get_formatter_tag_functions : unit -> formatter_tag_functions
Deprecated. Subsumed by Format.get_formatter_stag_functions .
OCamldoc 2023-02-12 Stdlib.Format(3o)
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