DIRECTORYAscii USING [TAB, CR, SP, DEL],IO USING [Backup, EndOf, EndOfStream, GetChar, PeekChar, STREAM],ArpaLex822,RefText USING [InlineAppendChar, ObtainScratch, ReleaseScratch],Rope USING [Cat, FromRefText, IsEmpty, ROPE];ArpaLex822Impl: CEDAR PROGRAMIMPORTS IO, RefText, RopeEXPORTS ArpaLex822 =BEGIN OPEN ArpaLex822;CharType: TYPE = {ctlType, crType, lwspType, specialType, atomType, illegalType};charType: ARRAY CHAR OF CharType;InternalGetToken: PROC [s: IO.STREAM] RETURNS [token: Rope.ROPE, tokType: TokenType] = {state: {start, inWhite, inAtom, inDelimited, slurpOne} _ start;nestable: BOOL;nestingLevel: INT _ 0;openingDelim, closingDelim: CHAR;TokenProc: CharProc = {SELECT state FROMstart => SELECT charType[char] FROMcrType =>IF NOT s.EndOf[] AND charType[s.PeekChar[]] = lwspType THEN {tokType _ whiteSpaceTok;state _ inWhite;}ELSE {tokType _ EOLTok;RETURN [TRUE, TRUE]};lwspType => {tokType _ whiteSpaceTok; state _ inWhite};specialType => SELECT char FROM'( => {state _ inDelimited;nestable _ TRUE;nestingLevel _ 1;openingDelim _ char;closingDelim _ ');tokType _ commentTok;};'[ => {state _ inDelimited;nestable _ FALSE;openingDelim _ char;closingDelim _ '];tokType _ domainLiteralTok;};'" => {state _ inDelimited;nestable _ FALSE;openingDelim _ char;closingDelim _ '";tokType _ quotedStringTok;};ENDCASE => {tokType _ specialTok; RETURN [TRUE, TRUE]};atomType => {tokType _ atomTok; state _ inAtom};ENDCASE => {tokType _ errorTok; RETURN [TRUE, TRUE]};inWhite => {IF char = Ascii.CR THEN {IF s.EndOf[] OR charType[s.PeekChar[]] # lwspType THENRETURN [TRUE, FALSE];}ELSERETURN[charType[char] # lwspType, charType[char] = lwspType];};inAtom => RETURN[charType[char] # atomType, charType[char] = atomType];inDelimited => {IF char = '\\ THENstate _ slurpOneELSE IF char = Ascii.CR THEN {IF s.EndOf[] OR charType[s.PeekChar[]] # lwspType THEN {tokType _ errorTok; -- token ends too soonRETURN [TRUE, FALSE];};}ELSE IF char = closingDelim THEN {IF nestable THEN nestingLevel _ nestingLevel - 1;IF nestingLevel <= 0 THEN quit _ TRUE;}ELSE IF char = openingDelim THENIF nestable THEN nestingLevel _ nestingLevel + 1ELSE {tokType _ errorTok; RETURN [TRUE, FALSE]} -- tried to nest illegally};slurpOne => state _ inDelimited;ENDCASE => ERROR;};  -- of TokenProctokType _ errorTok;token _ GetSequence[s, TokenProc]; -- sets tokType as side effect};LexToken: PUBLIC PROC [s: IO.STREAM] RETURNS [token, whiteSpace: Rope.ROPE, tokType: TokenType] = {whiteSpace _ NIL;DO[token, tokType] _ InternalGetToken[s];SELECT tokType FROMwhiteSpaceTok => whiteSpace _ whiteSpace.Cat[" "];commentTok => whiteSpace _ whiteSpace.Cat[token];ENDCASE => RETURN;ENDLOOP;};LexFieldName: PUBLIC PROC [s: IO.STREAM] RETURNS [fieldName: Rope.ROPE, fieldNameOk: BOOL] = {FieldProc: CharProc = {IF char = ': THEN RETURN [TRUE, FALSE];SELECT charType[char] FROMctlType, lwspType, crType => RETURN [TRUE, FALSE];ENDCASE => RETURN [FALSE, TRUE]; };fieldName _ GetSequence[s, FieldProc];IF fieldName.IsEmpty THEN fieldNameOk _ s.EndOf[] OR charType[s.PeekChar[]] = crTypeELSE fieldNameOk _ TRUE;};LexText: PUBLIC PROC [s: IO.STREAM] RETURNS [text: Rope.ROPE] = {lastWasCR: BOOL _ FALSE;TextProc: CharProc = {IF lastWasCR AND charType[char] # lwspType THEN {quit _ TRUE;include _ FALSE;}ELSE {quit _ FALSE;include _ TRUE;};lastWasCR _ char = Ascii.CR;};RETURN [GetSequence[s, TextProc]];};GetSequence: PUBLIC PROC [stream: IO.STREAM, charProc: CharProc] RETURNS [value: Rope.ROPE] = {buffer: REF TEXT _ RefText.ObtainScratch[512];buffer.length _ 0;DOchar: CHAR _ stream.GetChar[ ! IO.EndOfStream => EXIT];quit, include: BOOLEAN;[quit, include] _ charProc[char];IF include THEN buffer _ RefText.InlineAppendChar[buffer, char]ELSE IF quit THEN stream.Backup[char];IF quit THEN EXIT;ENDLOOP;value _ Rope.FromRefText[buffer];RefText.ReleaseScratch[buffer];};FOR c: CHAR IN [0C..37C] DOcharType[c] _ ctlType;ENDLOOP;FOR c: CHAR IN [41C..176C] DOcharType[c] _ atomType;ENDLOOP;charType[Ascii.CR] _ crType;charType[Ascii.TAB] _ lwspType;charType[Ascii.SP] _ lwspType;charType['"] _ specialType;charType['\\] _ specialType;charType['(] _ specialType;charType[')] _ specialType;charType['[] _ specialType;charType[']] _ specialType;charType['<] _ specialType;charType['>] _ specialType;charType['@] _ specialType;charType['.] _ specialType;charType[',] _ specialType;charType[':] _ specialType;charType[';] _ specialType;charType[Ascii.DEL] _ ctlType;FOR c: CHAR IN [200C..377C] DOcharType[c] _ illegalType;ENDLOOP;END.   °  ArpaLex822Impl.mesa, Implementation of RFC 822 lexical analyzer.HGM, March 8, 1984 10:08:21 pm PSTDavid Nichols, July 13, 1983 3:17 pmLast Edited by: Taft, February 5, 1984 11:53:10 am PSTHGM, March 8, 1984 10:08:21 pm PSTJohn Larson, October 10, 1987 5:01:34 pm PDTGet a token of any type from s, including white space and comments.Get a normal token from s and return the text of the token, the white space and comments following the token, and the type of token that was found.  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