[Cyan]<DATools6.0>CDCommon22>TokenIO.mesa!1

TokenIO.mesa

by Christian Jacobi, August 24, 1983 3:10 pm

last edited by Christian Jacobi, September 19, 1985 4:05:26 am PDT

DIRECTORY

IO, Rope;

TokenIO: CEDAR DEFINITIONS =

BEGIN

Input output in tokenized form. Allows grouping of tokens to clusters with a push and a popflag.

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

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

END.