src/Pure/General/pretty.ML

basic formatting of pretty trees;
line-up ML vs. Scala sources;

(*  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
  val add_mode: string -> (string -> int -> 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 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 setmargin: int -> unit
  val setmp_margin_CRITICAL: int -> ('a -> 'b) -> 'a -> 'b
  val setdepth: int -> unit
  val to_ML: T -> ML_Pretty.pretty
  val from_ML: ML_Pretty.pretty -> T
  val symbolicN: string
  val output_buffer: T -> Buffer.T
  val output: T -> output
  val string_of: T -> string
  val str_of: T -> string
  val writeln: T -> unit
  type pp
  val pp: (term -> T) * (typ -> T) * (sort -> T) * (class list -> T) * (arity -> T) -> pp
  val term: pp -> term -> T
  val typ: pp -> typ -> T
  val sort: pp -> sort -> T
  val classrel: pp -> class list -> T
  val arity: pp -> arity -> T
  val string_of_term: pp -> term -> string
  val string_of_typ: pp -> typ -> string
  val string_of_sort: pp -> sort -> string
  val string_of_classrel: pp -> class list -> string
  val string_of_arity: pp -> arity -> string
end;

structure Pretty: PRETTY =
struct

(** print mode operations **)

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

local
  val default = {indent = default_indent};
  val modes = Unsynchronized.ref (Symtab.make [("", default)]);
in
  fun add_mode name indent = CRITICAL (fn () =>
    Unsynchronized.change modes (Symtab.update_new (name, {indent = indent})));
  fun get_mode () =
    the_default default (Library.get_first (Symtab.lookup (! 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 **)

datatype T =
  Block of (output * output) * T list * int * int |  (*markup output, body, indentation, length*)
  String of output * int |                           (*text, length*)
  Break of bool * int;                               (*mandatory flag, width if not taken*)

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, 2);

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.none;
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 = markup m [prt];
fun keyword name = mark (Markup.keyword name) (str name);
fun command name = mark (Markup.command name) (str name);

fun markup_chunks m prts = markup m (fbreaks prts);
val chunks = markup_chunks Markup.none;
fun chunks2 prts = blk (0, flat (Library.separate [fbrk, fbrk] (map single prts)));

fun block_enclose (p1, p2) ps = chunks [(block  o fbreaks) (p1 :: ps), p2];

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 **)

(* margin *)

fun make_margin_info m =
 {margin = m,                   (*right margin, or page width*)
  breakgain = m div 20,         (*minimum added space required of a break*)
  emergencypos = m div 2};      (*position too far to right*)

val margin_info = Unsynchronized.ref (make_margin_info 76);
fun setmargin m = margin_info := make_margin_info m;
fun setmp_margin_CRITICAL m f = setmp_CRITICAL margin_info (make_margin_info m) f;


(* depth limitation *)

val depth = Unsynchronized.ref 0;   (*maximum depth; 0 means no limit*)
fun setdepth dp = (depth := dp);

local
  fun pruning dp (Block (m, bes, indent, _)) =
        if dp > 0
        then block_markup m (indent, map (pruning (dp - 1)) bes)
        else str "..."
    | pruning _ e = e;
in
  fun prune e = if ! depth > 0 then pruning (! depth) e else e;
end;


(* 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) = Break (true, 0) :: es
  | forcenext (e :: es) = e :: forcenext es;

(*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 {emergencypos, ...} = ! margin_info;
            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) =>
          let val {margin, breakgain, ...} = ! margin_info in
            (*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)
          end
      | String str => format (es, block, after) (string str text));

in

fun formatted e = #tx (format ([prune e], (Buffer.empty, 0), 0) empty);

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.markup Markup.fbreak (Buffer.add (output_spaces 1));
  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 (false, wd)) = Buffer.add (output_spaces wd)
      | fmt (Break (true, _)) = Buffer.add (output_spaces 1);
  in fmt (prune prt) Buffer.empty end;


(* 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;


(* output interfaces *)

val symbolicN = "pretty_symbolic";

fun output_buffer prt =
  if print_mode_active symbolicN then symbolic prt
  else formatted prt;

val output = Buffer.content o output_buffer;
val string_of = Output.escape o output;
val str_of = Output.escape o Buffer.content o unformatted;
val writeln = Output.writeln o string_of;



(** abstract pretty printing context **)

datatype pp =
  PP of (term -> T) * (typ -> T) * (sort -> T) * (class list -> T) * (arity -> T);

val pp = PP;

fun pp_fun f (PP x) = f x;

val term     = pp_fun #1;
val typ      = pp_fun #2;
val sort     = pp_fun #3;
val classrel = pp_fun #4;
val arity    = pp_fun #5;

val string_of_term     = string_of oo term;
val string_of_typ      = string_of oo typ;
val string_of_sort     = string_of oo sort;
val string_of_classrel = string_of oo classrel;
val string_of_arity    = string_of oo arity;

end;