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[smlnj] View of /sml/trunk/src/smlnj-lib/Util/format-comb.sml
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View of /sml/trunk/src/smlnj-lib/Util/format-comb.sml

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Revision 1193 - (download) (annotate)
Thu May 16 18:44:04 2002 UTC (17 years, 6 months ago) by jhr
File size: 2650 byte(s)
  Bringing the Yale repository upto date (see CHANGES file for details).
(* format-comb.sml
 * COPYRIGHT (c) 2002 Bell Labs, Lucent Technologies
 *   Well-typed "printf" for SML, aka "Unparsing Combinators".
 *     This code was written by Matthias Blume (2002).  Inspiration
 *     obtained from Olivier Danvy's "Functional Unparsing" work.
 * See format-comb-sig.sml for details.

structure FormatComb :> FORMAT_COMB =

    type 'a format         = string list -> 'a
    type ('a, 'b) fragment = 'a format -> 'b format
    type 'a glue           = ('a, 'a) fragment
    type ('a, 't) element  = ('a, 't -> 'a) fragment

    type place = int * int -> int
    fun left (a, i)   = a - i
    fun center (a, i) = Int.quot (a - i, 2)
    fun right (a, i)  = 0

	(* Generic padding, trimming, and fitting.  Nestability
	 * is achieved by remembering the current state s, passing
	 * a new empty one to the fragment, adjusting the output
	 * from that, and fitting the result back into the remembered
	 * state. ("States" are string lists and correspond to
	 * output coming from fragments to the left of the current point.) *)
	fun ptf adj pl n fr fm s = let
	    fun work s' = let
		val x' = concat (rev s')
		val sz = size x'
		adj (x', sz, n, pl (sz, n)) :: s
	    (fr (fm o work)) []

	val padRight = StringCvt.padRight #" "
	val padLeft = StringCvt.padLeft #" "
	fun pad0 (s, sz, n, off) = padRight n (padLeft (sz - off) s)
	fun trim0 (s, _, n, off) = String.substring (s, off, n)
	fun pad1 (arg as (s, sz, n, _)) = if n < sz then s else pad0 arg
	fun trim1 (arg as (s, sz, n, _)) = if n > sz then s else trim0 arg
	fun fit1 (arg as (_, sz, n, _)) = (if n < sz then trim0 else pad0) arg
	fun format' rcv fr   = fr (rcv o rev) []
        fun format fr        = format' concat fr

	fun using cvt fm x a = fm (cvt a :: x)

        fun int fm           = using Int.toString fm
	fun real fm          = using Real.toString fm
	fun bool fm          = using Bool.toString fm
	fun string fm        = using (fn x => x) fm
	fun string' fm       = using String.toString fm
	fun char fm          = using String.str fm
	fun char' fm         = using Char.toString fm

	fun int' rdx fm      = using (Int.fmt rdx) fm
	fun real' rfmt fm    = using (Real.fmt rfmt) fm

	fun pad place        = ptf pad1 place
	fun trim place       = ptf trim1 place
	fun fit place        = ptf fit1 place

    fun padl n = pad left n
    fun padr n = pad right n

    fun glue e a fm x = e fm x a

    fun nothing fm    = fm
    fun text s        = glue string s
    fun sp n          = pad left n nothing
    fun nl fm         = text "\n" fm
    fun tab fm        = text "\t" fm


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