(*  Title:      Pure/General/pretty.ML

     Author:     Lawrence C Paulson, Cambridge University Computer Laboratory

     Author:     Markus Wenzel, TU Munich

 Generic pretty printing module.

 Loosely based on

   D. C. Oppen, "Pretty Printing",

   ACM Transactions on Programming Languages and Systems (1980), 465-483.

 The object to be printed is given as a tree with indentation and line

 breaking information.  A "break" inserts a newline if the text until

 the next break is too long to fit on the current line.  After the newline,

 text is indented to the level of the enclosing block.  Normally, if a block

 is broken then all enclosing blocks will also be broken.  Only "inconsistent

 breaks" are provided.

 The stored length of a block is used in breakdist (to treat each inner block as

 a unit for breaking).

 *)

 signature PRETTY =

 sig

   val default_indent: string -> int -> Output.output

   val add_mode: string -> (string -> int -> Output.output) -> unit

   type T

   val str: string -> T

   val brk: int -> T

   val fbrk: T

   val breaks: T list -> T list

   val fbreaks: T list -> T list

   val blk: int * T list -> T

   val block: T list -> T

   val strs: string list -> T

   val markup: Markup.T -> T list -> T

   val mark: Markup.T -> T -> T

   val mark_str: Markup.T * string -> T

   val marks_str: Markup.T list * string -> T

   val keyword: string -> T

   val command: string -> T

   val markup_chunks: Markup.T -> T list -> T

   val chunks: T list -> T

   val chunks2: T list -> T

   val block_enclose: T * T -> T list -> T

   val quote: T -> T

   val backquote: T -> T

   val separate: string -> T list -> T list

   val commas: T list -> T list

   val enclose: string -> string -> T list -> T

   val enum: string -> string -> string -> T list -> T

   val position: Position.T -> T

   val list: string -> string -> T list -> T

   val str_list: string -> string -> string list -> T

   val big_list: string -> T list -> T

   val indent: int -> T -> T

   val unbreakable: T -> T

   val margin_default: int Unsynchronized.ref

   val symbolicN: string

   val output_buffer: int option -> T -> Buffer.T

   val output: int option -> T -> Output.output

   val string_of_margin: int -> T -> string

   val string_of: T -> string

   val str_of: T -> string

   val writeln: T -> unit

   val to_ML: T -> ML_Pretty.pretty

   val from_ML: ML_Pretty.pretty -> T

 end;

 structure Pretty: PRETTY =

 struct

 (** print mode operations **)

 fun default_indent (_: string) = Symbol.spaces;

 local

   val default = {indent = default_indent};

   val modes = Synchronized.var "Pretty.modes" (Symtab.make [("", default)]);

 in

   fun add_mode name indent =

     Synchronized.change modes (Symtab.update_new (name, {indent = indent}));

   fun get_mode () =

     the_default default

       (Library.get_first (Symtab.lookup (Synchronized.value modes)) (print_mode_value ()));

 end;

 fun mode_indent x y = #indent (get_mode ()) x y;

 val output_spaces = Output.output o Symbol.spaces;

 val add_indent = Buffer.add o output_spaces;

 (** printing items: compound phrases, strings, and breaks **)

 abstype T =

     Block of (Output.output * Output.output) * T list * int * int

       (*markup output, body, indentation, length*)

   | String of Output.output * int  (*text, length*)

   | Break of bool * int  (*mandatory flag, width if not taken*)

 with

 fun length (Block (_, _, _, len)) = len

   | length (String (_, len)) = len

   | length (Break (_, wd)) = wd;

 (** derived operations to create formatting expressions **)

 val str = String o Output.output_width;

 fun brk wd = Break (false, wd);

 val fbrk = Break (true, 1);

 fun breaks prts = Library.separate (brk 1) prts;

 fun fbreaks prts = Library.separate fbrk prts;

 fun block_markup m (indent, es) =

   let

     fun sum [] k = k

       | sum (e :: es) k = sum es (length e + k);

   in Block (m, es, indent, sum es 0) end;

 fun markup_block m arg = block_markup (Markup.output m) arg;

 val blk = markup_block Markup.empty;

 fun block prts = blk (2, prts);

 val strs = block o breaks o map str;

 fun markup m prts = markup_block m (0, prts);

 fun mark m prt = if m = Markup.empty then prt else markup m [prt];

 fun mark_str (m, s) = mark m (str s);

 fun marks_str (ms, s) = fold_rev mark ms (str s);

 fun keyword name = mark_str (Markup.keyword, name);

 fun command name = mark_str (Markup.command, name);

 fun markup_chunks m prts = markup m (fbreaks prts);

 val chunks = markup_chunks Markup.empty;

 fun chunks2 prts = blk (0, flat (Library.separate [fbrk, fbrk] (map single prts)));

 fun block_enclose (prt1, prt2) prts = chunks [block (fbreaks (prt1 :: prts)), prt2];

 fun quote prt = blk (1, [str "\"", prt, str "\""]);

 fun backquote prt = blk (1, [str "`", prt, str "`"]);

 fun separate sep prts =

   flat (Library.separate [str sep, brk 1] (map single prts));

 val commas = separate ",";

 fun enclose lpar rpar prts =

   block (str lpar :: (prts @ [str rpar]));

 fun enum sep lpar rpar prts = enclose lpar rpar (separate sep prts);

 val position =

   enum "," "{" "}" o map (fn (x, y) => str (x ^ "=" ^ y)) o Position.properties_of;

 val list = enum ",";

 fun str_list lpar rpar strs = list lpar rpar (map str strs);

 fun big_list name prts = block (fbreaks (str name :: prts));

 fun indent 0 prt = prt

   | indent n prt = blk (0, [str (Symbol.spaces n), prt]);

 fun unbreakable (Break (_, wd)) = String (output_spaces wd, wd)

   | unbreakable (Block (m, es, indent, wd)) = Block (m, map unbreakable es, indent, wd)

   | unbreakable (e as String _) = e;

 (** formatting **)

 (* formatted output *)

 local

 type text = {tx: Buffer.T, ind: Buffer.T, pos: int, nl: int};

 val empty: text =

  {tx = Buffer.empty,

   ind = Buffer.empty,

   pos = 0,

   nl = 0};

 fun newline {tx, ind = _, pos = _, nl} : text =

  {tx = Buffer.add (Output.output "\n") tx,

   ind = Buffer.empty,

   pos = 0,

   nl = nl + 1};

 fun control s {tx, ind, pos: int, nl} : text =

  {tx = Buffer.add s tx,

   ind = ind,

   pos = pos,

   nl = nl};

 fun string (s, len) {tx, ind, pos: int, nl} : text =

  {tx = Buffer.add s tx,

   ind = Buffer.add s ind,

   pos = pos + len,

   nl = nl};

 fun blanks wd = string (output_spaces wd, wd);

 fun indentation (buf, len) {tx, ind, pos, nl} : text =

   let val s = Buffer.content buf in

    {tx = Buffer.add (mode_indent s len) tx,

     ind = Buffer.add s ind,

     pos = pos + len,

     nl = nl}

   end;

 (*Add the lengths of the expressions until the next Break; if no Break then

   include "after", to account for text following this block.*)

 fun breakdist (Break _ :: _, _) = 0

   | breakdist (Block (_, _, _, len) :: es, after) = len + breakdist (es, after)

   | breakdist (String (_, len) :: es, after) = len + breakdist (es, after)

   | breakdist ([], after) = after;

 (*Search for the next break (at this or higher levels) and force it to occur.*)

 fun forcenext [] = []

   | forcenext (Break _ :: es) = fbrk :: es

   | forcenext (e :: es) = e :: forcenext es;

 in

 fun formatted margin input =

   let

     val breakgain = margin div 20;     (*minimum added space required of a break*)

     val emergencypos = margin div 2;   (*position too far to right*)

     (*es is list of expressions to print;

       blockin is the indentation of the current block;

       after is the width of the following context until next break.*)

     fun format ([], _, _) text = text

       | format (e :: es, block as (_, blockin), after) (text as {ind, pos, nl, ...}) =

           (case e of

             Block ((bg, en), bes, indent, _) =>

               let

                 val pos' = pos + indent;

                 val pos'' = pos' mod emergencypos;

                 val block' =

                   if pos' < emergencypos then (ind |> add_indent indent, pos')

                   else (add_indent pos'' Buffer.empty, pos'');

                 val btext: text = text

                   |> control bg

                   |> format (bes, block', breakdist (es, after))

                   |> control en;

                 (*if this block was broken then force the next break*)

                 val es' = if nl < #nl btext then forcenext es else es;

               in format (es', block, after) btext end

           | Break (force, wd) =>

               (*no break if text to next break fits on this line

                 or if breaking would add only breakgain to space*)

               format (es, block, after)

                 (if not force andalso

                     pos + wd <= Int.max (margin - breakdist (es, after), blockin + breakgain)

                   then text |> blanks wd  (*just insert wd blanks*)

                   else text |> newline |> indentation block)

           | String str => format (es, block, after) (string str text));

   in

     #tx (format ([input], (Buffer.empty, 0), 0) empty)

   end;

 end;

 (* special output *)

 (*symbolic markup -- no formatting*)

 fun symbolic prt =

   let

     fun out (Block ((bg, en), [], _, _)) = Buffer.add bg #> Buffer.add en

       | out (Block ((bg, en), prts, indent, _)) =

           Buffer.add bg #> Buffer.markup (Markup.block indent) (fold out prts) #> Buffer.add en

       | out (String (s, _)) = Buffer.add s

       | out (Break (false, wd)) = Buffer.markup (Markup.break wd) (Buffer.add (output_spaces wd))

       | out (Break (true, _)) = Buffer.add (Output.output "\n");

   in out prt Buffer.empty end;

 (*unformatted output*)

 fun unformatted prt =

   let

     fun fmt (Block ((bg, en), prts, _, _)) = Buffer.add bg #> fold fmt prts #> Buffer.add en

       | fmt (String (s, _)) = Buffer.add s

       | fmt (Break (_, wd)) = Buffer.add (output_spaces wd);

   in fmt prt Buffer.empty end;

 (* output interfaces *)

 val margin_default = Unsynchronized.ref 76;  (*right margin, or page width*)

 val symbolicN = "pretty_symbolic";

 fun output_buffer margin prt =

   if print_mode_active symbolicN then symbolic prt

   else formatted (the_default (! margin_default) margin) prt;

 val output = Buffer.content oo output_buffer;

 fun string_of_margin margin = Output.escape o output (SOME margin);

 val string_of = Output.escape o output NONE;

 val str_of = Output.escape o Buffer.content o unformatted;

 val writeln = Output.writeln o string_of;

 (** ML toplevel pretty printing **)

 fun to_ML (Block (m, prts, ind, _)) = ML_Pretty.Block (m, map to_ML prts, ind)

   | to_ML (String s) = ML_Pretty.String s

   | to_ML (Break b) = ML_Pretty.Break b;

 fun from_ML (ML_Pretty.Block (m, prts, ind)) = block_markup m (ind, map from_ML prts)

   | from_ML (ML_Pretty.String s) = String s

   | from_ML (ML_Pretty.Break b) = Break b;

 end;

 end;