PRETTY_PRINT-sig.sml

(*
 * (c) Andreas Rossberg 1999-2007
 *
 * A generic pretty printer.
 *
 * Based on:
 *    Philip Wadler. "A prettier printer"
 *    http://cm.bell-labs.com/cm/cs/who/wadler/
 * and Christian Lindig's port to OCaml.
 *
 * The semantics has been extended to allow 4 different kinds of
 * groups (`boxes'), 2 modes of nesting, and varying break representations.
 * This is no more easily described by an algebra though, and the `below'
 * combinator looses optimality.
 *)

signature PRETTY_PRINT =
sig
    type doc

    val empty :    doc               (* empty document *)
    val break :    doc               (* space or line break *)
    val ebreak :   doc               (* empty or line break *)
    val text :     string -> doc     (* raw text *)

    val ^^ :       doc * doc -> doc  (* concatenation *)
    val ^/^ :      doc * doc -> doc  (* concatenation with break *)

    val hbox :     doc -> doc        (* horizontal box *)
    val vbox :     doc -> doc        (* vertical box *)
    val fbox :     doc -> doc        (* fill box (h and v) *)
    val abox :     doc -> doc        (* auto box (h or v) *)

    val nest :     int -> doc -> doc (* indentation by k char's *)
    val below :    doc -> doc        (* keep current indentation *)

    val isEmpty :  doc -> bool

    val toString : doc * int -> string
    val output :   TextIO.outstream * doc * int -> unit
end;