; Tokens out of characters. ; ; A token is a run of characters with whitespace or a comment on either side, or anything ; between a pair of quotes. That is the whole of the lexical grammar: SplitBit assembly has ; no operators, no punctuation and no line continuation, so there is nothing here that has ; to look ahead more than one character. ; ; ONE CHARACTER OF LOOKAHEAD, and it is held here rather than in the reader. A word ends ; when something that is not part of it turns up, and that something has already been read ; by the time anyone knows - so it is put in TokPending and taken again next time. Keeping ; it at this level rather than pushing it back into the reader means the line number needs ; no arithmetic: srcNext counted the newline when it handed it out, and it stays counted. ; ; Zero means "nothing held", which is safe because a source file is text and a text file ; has no zero bytes in it. A file that did would be rejected as unassemblable long before ; the difference showed. ; ; Written by Anachronaut #Program ; The next token, into TokText with a zero after it. Q is zero if there was one. ; ; TokLength is how long it is, TokString says whether it arrived in quotes, and TokLine is ; the line it STARTED on - captured before the token is read, because a token ending in a ; newline has already moved the reader on to the next line by the time it is finished. tokNext: SETD.0 TokHeld LDA.0 BRA tokFresh RSTA STA.0 RSTA RSTB CCF ADD ; The one that was handed back, exactly as it was. RET tokFresh: RSTA SETD.0 TokString STA.0 tokSkip: CALL tokGet BNQ tokEnded CALL tokIsSpace BRQ tokSkip SETD.0 TokChar LDA.0 INIB 0x3B ; A semicolon starts a comment. XOR BNQ tokBegin tokComment: ; ---- Thrown away by the reader, not read one character at a time ---- ; ; This used to walk the comment through tokGet and srcNext, classifying every byte of it on ; the way to discarding it. Comments are most of what this assembler reads - 87 per cent of ; what a small program pulls in, once the libraries it includes are counted - so it was most ; of the work, and all of it thrown away. ; ; A pushed back character cannot be sitting there: this is only reached from tokSkip, which ; got the semicolon out of tokGet and did not put anything back. CALL srcSkipComment BNQ tokEnded BRI tokSkip tokBegin: ; Where it starts, for anything that has to complain about it later. SETD.0 TokLine SETD.2 SrcLine CALL numSet RSTA SETD.0 TokLength STA.0 SETD.0 TokText SETD.1 TokPointer STD.0.1 SETD.0 TokChar LDA.0 INIB 0x22 ; A quote starts a string. XOR BNQ tokWord INIA 0d1 SETD.0 TokString STA.0 tokStringLoop: CALL tokGet BNQ tokDone ; The file ended inside a string. Take what there is; the ; classifier will have something to complain about. SETD.0 TokChar LDA.0 INIB 0x22 XOR BRQ tokDone CALL tokAppend BRI tokStringLoop tokWord: CALL tokAppend tokWordLoop: CALL tokGet BNQ tokDone CALL tokIsSpace BRQ tokHoldDone SETD.0 TokChar LDA.0 INIB 0x3B XOR BRQ tokHoldDone ; A comment butting straight up against a word ends it. CALL tokAppend BRI tokWordLoop tokHoldDone: ; Whatever ended the word was not part of it, so it goes back to be looked at again. SETD.0 TokChar LDA.0 SETD.0 TokPending STA.0 tokDone: SETD.1 TokPointer LDD.0.1 RSTA STA.0 ; The zero that makes it a string. RSTA RSTB CCF ADD ; Q is zero: there was a token. RET tokEnded: RSTA SETD.0 TokLength STA.0 SETD.0 TokText STA.0 RSTA INIB 0d1 CCF ADD ; Q is not zero: the source is finished. RET ; Puts the held character back into the file it came from, leaving nothing in hand. ; ; This is what #Include calls before the reader puts the current file aside. The character ; the tokenizer is holding was read from that file and has not been used, so it goes back ; into it; there is then nothing to carry across the include and nothing to hand back at a ; moment that might land in the middle of a word. tokUnread: SETD.0 TokPending LDA.0 BRA tokUnreadDone CALL srcStepBack RSTA SETD.0 TokPending STA.0 tokUnreadDone: RET ; Hands the token just read back, so that the next tokNext produces it again. ; ; ONE TOKEN, and only where nothing has changed it since. The Vector Segment needs it: a ; name there may be followed by a number, by a handler, or by the next line's name, and ; which it is cannot be known without looking. Do NOT use it after anything that alters ; TokText - a label definition with its colon written over would come back as a use of the ; name rather than as a definition of it. tokBack: INIA 0d1 SETD.0 TokHeld STA.0 RET ; The next character, into TokChar. Q is zero if there was one. Takes the held one first. tokGet: SETD.0 TokPending LDA.0 BRA tokGetFresh SETD.0 TokChar STA.0 RSTA SETD.0 TokPending STA.0 RSTA RSTB CCF ADD RET tokGetFresh: CALL srcNext BNQ tokGetNone SETD.0 SrcChar LDA.0 SETD.0 TokChar STA.0 RSTA RSTB CCF ADD RET tokGetNone: RSTA INIB 0d1 CCF ADD RET ; Adds TokChar to the token being built, unless it is already as long as one may be. ; ; A token that runs over is truncated rather than refused, and the classifier refuses it ; afterwards: nothing 255 characters long is a valid mnemonic, literal or label, so the ; error that comes out names what was wrong with it rather than only how long it was. tokAppend: SETD.0 TokLength LDA.0 INIB 0xFF XOR BRQ tokAppendFull SETD.1 TokPointer LDD.0.1 SETD.2 TokChar LDA.2 STA.0 INCD.0 STD.0.1 SETD.0 TokLength LDA.0 INCA STA.0 tokAppendFull: RET ; Q is zero if TokChar is whitespace: a space, or anything in the run from tab to carriage ; return, which is what the C library calls a space and what the other assembler uses. tokIsSpace: SETD.0 TokChar LDA.0 INIB 0x20 XOR BRQ tokSpaceYes SETD.0 TokChar LDA.0 INIB 0x09 CCF SUB BRC tokSpaceNo ; Below a tab. SETD.0 TokChar LDA.0 INIB 0x0E CCF SUB BNC tokSpaceNo ; Past a carriage return. tokSpaceYes: RSTA RSTB CCF ADD RET tokSpaceNo: RSTA INIB 0d1 CCF ADD RET #Data TokLine: 0x00 0x00 TokPointer: 0x00 0x00 TokLength: 0x00 TokString: 0x00 TokChar: 0x00 TokPending: 0x00 TokHeld: 0x00 ; As long as a token may be, and one more for the zero. The other assembler stops at the ; same 255, and the limit is worth matching rather than choosing again. TokText: #Reserve 0d256