(*  Title:      Pure/basis.ML

    ID:         $Id$

    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory

    Copyright   1993  University of Cambridge

Basis Library emulation.

Needed for Poly/ML and Standard ML of New Jersey version 0.93 to 1.08.

Full compatibility cannot be obtained using a file: what about char constants?

*)

exception Subscript;

structure Bool =

  struct

  fun toString true  = "true"

    | toString false = "false"

  end;

structure Option =

  struct

  exception Option

  datatype 'a option = NONE | SOME of 'a

  fun getOpt (SOME v, _) = v

    | getOpt (NONE,   a) = a

  fun isSome (SOME _) = true 

    | isSome NONE     = false

  fun valOf (SOME v) = v

    | valOf NONE     = raise Option

  end;

structure Int =

  struct

  fun toString (i: int) = makestring i;

  fun max (x, y) = if x < y then y else x : int;

  fun min (x, y) = if x < y then x else y : int;

  end;

structure List =

  struct

  exception Empty

  fun last []      = raise Empty

    | last [x]     = x

    | last (x::xs) = last xs;

  fun nth (xs, n) =

      let fun h []      _ = raise Subscript

	    | h (x::xs) n = if n=0 then x else h xs (n-1)

      in if n<0 then raise Subscript else h xs n end;

  fun drop (xs, n) =

      let fun h xs      0 = xs

	    | h []      n = raise Subscript

	    | h (x::xs) n = h xs (n-1)

      in if n<0 then raise Subscript else h xs n end;

  fun take (xs, n) =

      let fun h xs      0 = []

	    | h []      n = raise Subscript

	    | h (x::xs) n = x :: h xs (n-1)

      in if n<0 then raise Subscript else h xs n end;

  fun concat []      = []

    | concat (l::ls) = l @ concat ls;

  fun mapPartial f []      = []

    | mapPartial f (x::xs) = 

         (case f x of Option.NONE   => mapPartial f xs

                    | Option.SOME y => y :: mapPartial f xs);

  fun find _ []        = Option.NONE

    | find p (x :: xs) = if p x then Option.SOME x else find p xs;

  (*copy the list preserving elements that satisfy the predicate*)

  fun filter p [] = []

    | filter p (x :: xs) = if p x then x :: filter p xs else filter p xs;

  (*Partition list into elements that satisfy predicate and those that don't.

    Preserves order of elements in both lists.*)

  fun partition (p: 'a->bool) (ys: 'a list) : ('a list * 'a list) =

      let fun part ([], answer) = answer

	    | part (x::xs, (ys, ns)) = if p(x)

	      then  part (xs, (x::ys, ns))

	      else  part (xs, (ys, x::ns))

      in  part (rev ys, ([], []))  end;

  end;

structure ListPair =

  struct

  fun zip ([], [])      = []

    | zip (x::xs,y::ys) = (x,y) :: zip(xs,ys);

  fun unzip [] = ([],[])

    | unzip((x,y)::pairs) =

	  let val (xs,ys) = unzip pairs

	  in  (x::xs, y::ys)  end;

  fun map f ([], [])      = []

    | map f (x::xs,y::ys) = f(x,y) :: map f (xs,ys);

  fun exists p =

    let fun boolf ([], [])      = false

	  | boolf (x::xs,y::ys) = p(x,y) orelse boolf (xs,ys)

    in boolf end;

  fun all p =

    let fun boolf ([], [])      = true

	  | boolf (x::xs,y::ys) = p(x,y) andalso boolf (xs,ys)

    in boolf end;

  end;

structure TextIO =

  struct

  type instream = instream

  and  outstream = outstream

  exception Io of {name: string, function: string, cause: exn}

  val stdIn 	= std_in

  val stdOut 	= std_out

  val openIn 	= open_in

  val openAppend = open_append

  val openOut 	= open_out

  val closeIn 	= close_in

  val closeOut 	= close_out

  val inputN 	= input

  val inputAll  = fn is => inputN (is, 999999)

  val inputLine = input_line

  val endOfStream = end_of_stream

  val output 	= output

  val flushOut 	= flush_out

  end;

fun print s = (output (std_out, s); flush_out std_out);