[Indigo]<Chipndale>5.2>cd20>TokenIO.mesa!1

TokenIO.mesa

by Christian Jacobi August 24, 1983 3:10 pm

last edited by Christian Jacobi December 12, 1984 10:56:52 am PST

DIRECTORY

IO, Rope;

TokenIO: CEDAR DEFINITIONS =

BEGIN

Mark: TYPE = REF MarkRep;

MarkRep: TYPE;

WritingStopped: SIGNAL;

StopWriting: PROC [] = INLINE {stopWriting←TRUE};

-- causes next call of Write or Update to signal WritingStopped

-- (inside monitorlock; may be resumed or aborted)

-- AttachWriter invalidates a call of WritingStopped

-- inline for speed reason only

stopWriting: PRIVATE BOOL;

WriteInt: PROC [i: INT];

WriteAtom: PROC [a: ATOM];

WriteRope: PROC [r: Rope.ROPE];

WritePushFlag: PROC [a: ATOM←NIL];

WritePopFlag: PROC [];

MarkAndWriteInt: PROC [value: INT] RETURNS [Mark];

UpdateMark: PROC [mark: Mark, value: INT];

TokenType: TYPE = {atom, int, rope, pushFlag, popFlag, endOfStream, error};

Token: TYPE = RECORD [

kind: TokenType,

ref: REF←NIL -- either ATOM, Rope.ROPE, REF INT or NIL (Rope.ROPE or NIL if error)

];

-- kind = atom => ISTYPE[ref, ATOM]

-- kind = int => ISTYPE[ref, REF INT]

-- kind = rope => ISTYPE[ref, Rope.ROPE]

-- kind = pushFlag => ref=NIL or ISTYPE[ref, ATOM]

-- kind = popFlag => ref=NIL

-- kind = endOfStream => ref=NIL

-- kind = error => ref=NIL OR ISTYPE[ref, Rope.ROPE]

ReadToken: PROC [] RETURNS [Token];

ReadAgain: PROC [];

-- cause next call of ReadToken to get the same value as the last read

-- works only one level deep (reads again only the last value returned by ReadToken)

EncodingError: SIGNAL;

-- all read procedures SIGNAL EncodingError if read token is not as expected;

-- for emergeny error bypassing, the state may be changed in the debugger

-- and the computation continued; however, normal computation considers

-- EncodingError to be an ERROR, not a SIGNAL.

ReadInt: PROC [] RETURNS [INT];

ReadAtom: PROC [] RETURNS [ATOM];

ReadRope: PROC [] RETURNS [Rope.ROPE];

ReadPushFlag: PROC [] RETURNS [ATOM];

ReadPopFlag: PROC [];

-- Attaching TokenIo to STREAMS

-- while TokenIo is attached to a stream no other operations on this

-- stream should occur

Error: ERROR[why: Err, explanation: Rope.ROPE]; -- only on Attach or Release

Err: TYPE = {alreadyAttached, wrongVersion, other};

AttachReader: PROC [stream: IO.STREAM];

ReleaseReader: PROC [];

AttachWriter: PROC [stream: IO.STREAM];

ReleaseWriter: PROC [];

-- also invalidates marks

-- the routines may generate some standard IO signals and errors, however,

-- as few as possible

-- the Rope NIL and the Rope "" may read back correctly or exchanged

-- the ATOM NIL reads back correctly;

-- the ATOM "$" may be read back correctly or as NIL ATOM

END.