# Structure TextIO

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    (* TextIO -- SML Basis Library *)

    type elem   = Char.char
    type vector = string

    (* Text input *)

    type instream

    val openIn       : string -> instream
    val closeIn      : instream -> unit
    val input        : instream -> vector
    val inputAll     : instream -> vector
    val inputNoBlock : instream -> vector option
    val input1       : instream -> elem option
    val inputN       : instream * int -> vector
    val inputLine    : instream -> string option
    val endOfStream  : instream -> bool
    val lookahead    : instream -> elem option

    type cs (* character source state *)

    val scanStream   : ((char, cs) StringCvt.reader -> ('a, cs) StringCvt.reader)
                       -> instream -> 'a option

    val stdIn        : instream

    (* Text output *)

    type outstream

    val openOut      : string -> outstream
    val openAppend   : string -> outstream
    val closeOut     : outstream -> unit
    val output       : outstream * vector -> unit
    val output1      : outstream * elem -> unit
    val outputSubstr : outstream * substring -> unit
    val flushOut     : outstream -> unit

    val stdOut       : outstream
    val stdErr       : outstream

    val print        : string -> unit

    (*
       This structure provides input/output functions on text streams.
       The functions are state-based: reading from or writing to a stream
       changes the state of the stream.  The streams are buffered: output
       to a stream may not immediately affect the underlying file or
       device.

       Note that under DOS, Windows, OS/2, and MacOS, text streams will be
       `translated' by converting (e.g.) the double newline CRLF to a
       single newline character \n.

       [instream] is the type of state-based character input streams.

       [outstream] is the type of state-based character output streams.

       [elem] is the type char of characters.

       [vector] is the type of character vectors, that is, strings.

       TEXT INPUT:

       [openIn s] creates a new instream associated with the file named s.
       Raises Io.Io is file s does not exist or is not accessible.

       [closeIn istr] closes stream istr.  Has no effect if istr is closed
       already.  Further operations on istr will behave as if istr is at
       end of stream (that is, will return "" or NONE or true).

       [input istr] reads some elements from istr, returning a vector v of
       those elements.  The vector will be empty (size v = 0) if and only
       if istr is at end of stream or is closed.  May block (not return
       until data are available in the external world).

       [inputAll istr] reads and returns the string v of all characters
       remaining in istr up to end of stream.

       [inputNoBlock istr] returns SOME(v) if some elements v can be read
       without blocking; returns SOME("") if it can be determined without
       blocking that istr is at end of stream; returns NONE otherwise.  If
       istr does not support non-blocking input, raises
       Io.NonblockingNotSupported.

       [input1 istr] returns SOME(e) if at least one element e of istr is
       available; returns NONE if istr is at end of stream or is closed;
       blocks if necessary until one of these conditions holds.

       [inputN(istr, n)] returns the next n characters from istr as a
       string, if that many are available; returns all remaining
       characters if end of stream is reached before n characters are
       available; blocks if necessary until one of these conditions holds.
       (This is the behaviour of the `input' function prescribed in the
       1990 Definition of Standard ML).

       [inputLine istr] returns SOME ln, where ln is one line of text,
       including the terminating newline character.  If end of stream is
       reached before a newline character, then the remaining part of the
       stream is returned, with a newline character added.  If istr is at
       end of stream or is closed, then NONE is returned.

       [endOfStream istr] returns false if any elements are available in
       istr; returns true if istr is at end of stream or closed; blocks if
       necessary until one of these conditions holds.

       [lookahead istr] returns SOME(e) where e is the next element in the
       stream; returns NONE if istr is at end of stream or is closed;
       blocks if necessary until one of these conditions holds.  Does not
       advance the stream.

       [stdIn] is the buffered state-based standard input stream.

       [scanStream scan istr] turns the instream istr into a character
       source and applies the scanner `scan' to that source.  See
       StringCvt for more on character sources and scanners.  The Moscow
       ML implementation currently can backtrack only 512 characters, and
       raises Fail if the scanner backtracks further than that.

       TEXT OUTPUT:

       [openOut s] creates a new outstream associated with the file named
       s.  If file s does not exist, and the directory exists and is
       writable, then a new file is created.  If file s exists, it is
       truncated (any existing contents are lost).

       [openAppend s] creates a new outstream associated with the file
       named s.  If file s does not exist, and the directory exists and is
       writable, then a new file is created.  If file s exists, any
       existing contents are retained, and output goes at the end of the
       file.

       [closeOut ostr] closes stream ostr; further operations on ostr
       (except for additional close operations) will raise exception Io.Io.

       [output(ostr, v)] writes the string v on outstream ostr.

       [output1(ostr, e)] writes the character e on outstream ostr.

       [flushOut ostr] flushes the outstream ostr, so that all data
       written to ostr becomes available to the underlying file or device.

       [stdOut] is the buffered state-based standard output stream.

       [stdErr] is the unbuffered state-based standard error stream.  That
       is, it is always kept flushed, so flushOut(stdErr) is redundant.

       [print s] outputs s to stdOut and flushes immediately.

       The functions below are not yet implemented:

       [setPosIn(istr, i)] sets istr to the (untranslated) position i.
       Raises Io.Io if not supported on istr.

       [getPosIn istr] returns the (untranslated) current position of istr.
       Raises Io.Io if not supported on istr.

       [endPosIn istr] returns the (untranslated) last position of istr.
       Because of translation, one cannot expect to read
            endPosIn istr - getPosIn istr
       from the current position.

       [getPosOut ostr] returns the current position in stream ostr.
       Raises Io.Io if not supported on ostr.

       [endPosOut ostr] returns the ending position in stream ostr.
       Raises Io.Io if not supported on ostr.

       [setPosOut(ostr, i)] sets the current position in stream to ostr to
       i.  Raises Io.Io if not supported on ostr.

       [mkInstream sistr] creates a state-based instream from the
       functional instream sistr.

       [getInstream istr] returns the functional instream underlying the
       state-based instream istr.

       [setInstream(istr, sistr)] redirects istr, so that subsequent input
       is taken from the functional instream sistr.

       [mkOutstream sostr] creates a state-based outstream from the
       outstream sostr.

       [getOutstream ostr] returns the outstream underlying the
       state-based outstream ostr.

       [setOutstream(ostr, sostr)] redirects the outstream ostr so that
       subsequent output goes to sostr.
    *)

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Moscow ML 2.10