## `format`: pretty printing

  This module implements a pretty-printing facility to format text within ``pretty-printing boxes''. The pretty-printer breaks lines at specified break hints, and indents lines according to the box structure.

  Rule of thumb for casual users:
  use simple boxes (as obtained by `open_box 0`);
  use simple break hints (as obtained by `print_cut ()` that outputs a simple break hint, or by `print_space ()` that ouputs a space indicating a break hint);
  once a box is opened, display its material with basic printing functions (e. g. `print_int` and `print_string`);
  when the material for a box has been printed, call `close_box ()` to close the box;
  at the end of your routine, evaluate `print_newline ()` to close all remaining boxes and flush the pretty-printer.

  You may alternatively consider this module as providing an extension to the `printf` facility: you can simply add pretty-printing annotations to your regular printf formats, as explained below in the documentation of the function `fprintf`.

  The behaviour of pretty-printing commands is unspecified if there is no opened pretty-printing box. Each box opened via 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, the system closes all opened boxes and flushes all pending text (as with the `print_newline` function) after each phrase. Each phrase is therefore executed in the initial state of the pretty-printer.

### Boxes

    value open_box : int -> unit

  `open_box d` opens a new pretty-printing box with offset `d`. This box is the general purpose pretty-printing box. Material in this box is displayed ``horizontal or vertical'': break hints inside the box may lead to a new line, if there is no more room on the line to print the remainder of the box, or if a new line may lead to a new indentation (demonstrating the indentation of the box). When a new line is printed in the box, `d` is added to the current indentation.

    value close_box : unit -> unit

  Close the most recently opened pretty-printing box.

### Formatting functions

    value print_string : string -> unit

  `print_string str` prints `str` in the current box.

    value print_as : int -> string -> unit

  `print_as len str` prints `str` in the current box. The pretty-printer formats `str` as if it were of length `len`.

    value print_int : int -> unit

  Print an integer in the current box.

    value print_float : float -> unit

  Print a floating point number in the current box.

    value print_char : char -> unit

  Print a character in the current box.

    value print_bool : bool -> unit

  Print an boolean in the current box.

### Break hints

    value print_space : unit -> unit

  `print_space ()` is used to separate items (typically to print a space between two words). It indicates that the line may be split at this point. It either prints one space or splits the line. It is equivalent to `print_break 1 0`.

    value print_cut : unit -> unit

  `print_cut ()` is used to mark a good break position. It indicates that the line may be split at this point. It either prints nothing or splits the line. This allows line splitting at the current point, without printing spaces or adding indentation. It is equivalent to `print_break 0 0`.

    value print_break : int -> int -> unit

  Insert a break hint in a pretty-printing box. `print_break nspaces offset` indicates that the line may be split (a newline character is printed) at this point, if the contents of the current box does not fit on one line. If the line is split at that point, `offset` is added to the current indentation. If the line is not split, `nspaces` spaces are printed.

    value print_flush : unit -> unit

  Flush the pretty printer: all opened boxes are closed, and all pending text is displayed.

    value print_newline : unit -> unit

  Equivalent to `print_flush` followed by a new line.

    value force_newline : unit -> unit

  Force a newline in the current box. Not the normal way of pretty-printing, you should prefer break hints.

    value print_if_newline : unit -> unit

  Execute the next formatting command if the preceding line has just been split. Otherwise, ignore the next formatting command.

### Margin

    value set_margin : int -> unit

  `set_margin d` sets the value of the right margin to `d` (in characters): this value is used to detect line overflows that leads to split lines. Nothing happens if `d` is smaller than 2 or bigger than 999999999.

    value get_margin : unit -> int

  Return the position of the right margin.

### Maximum indentation limit

    value set_max_indent : int -> unit

  `set_max_indent d` sets the value of the maximum indentation limit to `d` (in characters): once this limit is reached, boxes are rejected to the left, if they do not fit on the current line. Nothing happens if `d` is smaller than 2 or bigger than 999999999.

    value get_max_indent : unit -> int

  Return the value of the maximum indentation limit (in characters).

### Formatting depth: maximum number of boxes allowed before ellipsis

    value set_max_boxes : int -> unit

  `set_max_boxes max` sets the maximum number of boxes simultaneously opened. Material inside boxes nested deeper is printed as an ellipsis (more precisely as the text returned by `get_ellipsis_text ()`). Nothing happens if `max` is not greater than 1.

    value get_max_boxes : unit -> int

  Return the maximum number of boxes allowed before ellipsis.

    value over_max_boxes : unit -> bool

  Test the maximum number of boxes allowed have already been opened.

### Advanced formatting

    value open_hbox : unit -> unit

  `open_hbox ()` opens a new pretty-printing box. This box is ``horizontal'': the line is not split in this box (new lines may still occur inside boxes nested deeper).

    value open_vbox : int -> unit

  `open_vbox d` opens a new pretty-printing box with offset `d`. This box is ``vertical'': every break hint inside this box leads to a new line. When a new line is printed in the box, `d` is added to the current indentation.

    value open_hvbox : int -> unit

  `open_hvbox d` opens a new pretty-printing box with offset `d`. This box is ``horizontal-vertical'': it behaves as an ``horizontal'' box if it fits on a single line, otherwise it behaves as a ``vertical'' box. When a new line is printed in the box, `d` is added to the current indentation.

    value open_hovbox : int -> unit

  `open_hovbox d` opens a new pretty-printing box with offset `d`. This box is ``horizontal or vertical'': break hints inside this box may lead to a new line, if there is no more room on the line to print the remainder of the box. When a new line is printed in the box, `d` is added to the current indentation.

### Tabulations

    value open_tbox : unit -> unit

  Open a tabulation box.

    value close_tbox : unit -> unit

  Close the most recently opened tabulation box.

    value print_tbreak : int -> int -> unit

  Break hint in a tabulation box. `print_tbreak spaces offset` moves the insertion point to the next tabulation (`spaces` being added to this position). Nothing occurs if insertion point is already on a tabulation mark. If there is no next tabulation on the line, then a newline is printed and the insertion point moves to the first tabulation of the box. If a new line is printed, `offset` is added to the current indentation.

    value set_tab : unit -> unit

  Set a tabulation mark at the current insertion point.

    value print_tab : unit -> unit

  `print_tab ()` is equivalent to `print_tbreak (0,0)`.

### Ellipsis

    value set_ellipsis_text : string -> unit

  Set the text of the ellipsis printed when too many boxes are opened (a single dot, `.`, by default).

    value get_ellipsis_text : unit -> string

  Return the text of the ellipsis.

### Redirecting formatter output

    value set_formatter_out_channel : out_channel -> unit

  Redirect the pretty-printer output to the given channel.

    value set_formatter_output_functions :
          (string -> int -> int -> unit) -> (unit -> unit) -> unit

  `set_formatter_output_functions out flush` redirects the pretty-printer output to the functions `out` and `flush`. The `out` function performs the pretty-printer 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 `flush` function is called whenever the pretty-printer is flushed using `print_flush` or `print_newline`.

    value get_formatter_output_functions :
            unit -> (string -> int -> int -> unit) * (unit -> unit)

  Return the current output functions of the pretty-printer.

### Multiple formatted output

    type formatter

  Abstract data type corresponding to a pretty-printer and all its machinery. Defining new pretty-printers permits the output of material in parallel on several channels. Parameters of the pretty-printer are local to the pretty-printer: margin, maximum indentation limit, maximum number of boxes simultaneously opened, ellipsis, and so on, are specific to each pretty-printer and may be fixed independently. A new formatter is obtained by calling the `make_formatter` function.

    value std_formatter : formatter

  The standard formatter used by the formatting functions above. It is defined using `make_formatter` with output function `output stdout` and flushing function `fun () -> flush stdout`.

    value err_formatter : formatter

  A formatter to use with formatting functions below for output to standard error. It is defined using `make_formatter` with output function `output stderr` and flushing function `fun () -> flush stderr`.

    value make_formatter :
            (string -> int -> int -> unit) -> (unit -> unit) -> formatter

  `make_formatter out flush` returns a new formatter that writes according to the output function `out`, and flushing function `flush`. Hence, a formatter to out channel `oc` is returned by `make_formatter (output oc) (fun () -> flush oc)`.

    value pp_open_hbox : formatter -> unit -> unit
    value pp_open_vbox : formatter -> int -> unit
    value pp_open_hvbox : formatter -> int -> unit
    value pp_open_hovbox : formatter -> int -> unit
    value pp_open_box : formatter -> int -> unit
    value pp_close_box : formatter -> unit -> unit
    value pp_print_string : formatter -> string -> unit
    value pp_print_as : formatter -> int -> string -> unit
    value pp_print_int : formatter -> int -> unit
    value pp_print_float : formatter -> float -> unit
    value pp_print_char : formatter -> char -> unit
    value pp_print_bool : formatter -> bool -> unit
    value pp_print_break : formatter -> int -> int -> unit
    value pp_print_cut : formatter -> unit -> unit
    value pp_print_space : formatter -> unit -> unit
    value pp_force_newline : formatter -> unit -> unit
    value pp_print_flush : formatter -> unit -> unit
    value pp_print_newline : formatter -> unit -> unit
    value pp_print_if_newline : formatter -> unit -> unit
    value pp_open_tbox : formatter -> unit -> unit
    value pp_close_tbox : formatter -> unit -> unit
    value pp_print_tbreak : formatter -> int -> int -> unit
    value pp_set_tab : formatter -> unit -> unit
    value pp_print_tab : formatter -> unit -> unit
    value pp_set_margin : formatter -> int -> unit
    value pp_get_margin : formatter -> unit -> int
    value pp_set_max_indent : formatter -> int -> unit
    value pp_get_max_indent : formatter -> unit -> int
    value pp_set_max_boxes : formatter -> int -> unit
    value pp_get_max_boxes : formatter -> unit -> int
    value pp_over_max_boxes : formatter -> unit -> bool
    value pp_set_ellipsis_text : formatter -> string -> unit
    value pp_get_ellipsis_text : formatter -> unit -> string
    value pp_set_formatter_out_channel : formatter -> out_channel -> unit
    value pp_set_formatter_output_functions : formatter ->
            (string -> int -> int -> unit) -> (unit -> unit) -> unit
    value pp_get_formatter_output_functions :
            formatter -> unit -> (string -> int -> int -> unit) * (unit -> unit)

  The basic functions to use with formatters. These functions are the basic ones: usual functions operating on the standard formatter are defined via partial evaluation of these primitives. For instance, `print_string` is equal to `pp_print_string std_formatter`.

    value fprintf : formatter -> ('a, formatter, unit) format -> 'a

  `fprintf ff format arg1 ... argN` formats the arguments `arg1` to `argN` according to the format string `format`, and outputs the resulting string on the formatter `ff`. The format 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. The pretty-printing indication characters are introduced by a `@` character, 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. Box type is one of `h`, `v`, `hv`, or `hov`, which stand respectively for an horizontal, vertical, ``horizontal-vertical'' and ``horizontal or vertical'' box.
  `]`: close the most recently opened pretty-printing box.
  `,`: output a good break as with `print_cut ()`.
  `` : output a space, as with `print_space ()`.
  `\n`: force a newline, as with `force_newline ()`.
  `;`: output a good break as with `print_break`. The `nspaces` and `offset` parameters of the break may be optionally specified with the following syntax: the `<` character, followed by an integer `nspaces` value, then an integer offset, and a closing `>` character.
  `.`: flush the pretty printer as with `print_newline ()`.
  `@`: a plain `@` character.

    value printf : ('a, formatter, unit) format -> 'a

  Same as `fprintf`, but output on `std_formatter`.

    value eprintf: ('a, formatter, unit) format -> 'a

  Same as `fprintf`, but output on `err_formatter`.