1.15 INPUT & READ Handlers

Input

Let user input a number at a '?' prompt.

Read

05F6	E5	Read	PUSH H
05F7	2A6D01		LHLD DATA_PROG_PTR
05FA	F6AF		ORI AF
05FB	AF		XRA A
05FC	325C01		STA INPUT_OR_READ
Preserve data prog ptr on stack and restore prog ptr to HL. This should point to the name of the variable to read data into. Note we also LXI over the syntax check for a comma that's done on subsequent reads.
05FF	E3		XTHL
0600	01....		LXI B,....
0601	CF	ReadNext	RST SyntaxCheck
0602	2C		','
Get variable value address in DE.
0603	CD1B07		CALL GetVar
Preserve prog ptr and get data prog ptr into HL.
0606	E3		XTHL
Preserve variable value address on stack.
0607	D5		PUSH D
Get byte of data part of program. If this is a comma seperator then we've found our data item and can jump ahead to GotDataItem
0608	7E		MOV A,M
0609	FE2C		CPI ','
060B	CA2006		JZ GotDataItem
If the next byte of data is not a null byte terminating the line then syntax error out.
060E	B7		ORA A
060F	C2D001		JNZ SyntaxError
If we're READ'ing data then jump ahead to find the next DATA statement.
0612	3A5C01		LDA INPUT_OR_READ
0615	B7		ORA A
0616	23		INX H
0617	C23606		JNZ NextDataLine+1
We've been called by the INPUT handler, and we have more inputs to take - the interpreter allows 'INPUT A,B,C' -type statement. So here we get the next input, only Bill has made a mistake here - he prints an unnecessary '?' , so the user gets two question marks for all inputs after the first one.
061A	3E3F		MVI A,'?'
061C	DF		RST OutChar
061D	CDC202		CALL InputLineWith'?'
Restore variable address, advance the data ptr so it points to the start of the next data item, and assign the data item to the variable.
0620	D1	GotDataItem	POP D
0621	23		INX H
0622	CD0705		CALL AssignVar
Get prog ptr off stack, and push data prog ptr, decrement prog ptr because AssignVar automatically advanced it, which we don't want.
0625	E3		XTHL
0626	2B		DCX H
Get next char of READ statement and jump back to ReadNext if the end of the line has not been reached.
0627	D7		RST NextChar
0628	C20106		JNZ ReadNext
End of READ statement reached.
062B	D1		POP D
062C	3A5C01		LDA INPUT_OR_READ
062F	B7		ORA A
0630	C8		RZ
0631	EB		XCHG
0632	C26E04		JNZ 046E
Loop to find the next DATA line. Here we get the data prog ptr off the stack, and PushNextWord so the address of the next line is on the stack.
0635	E1	NextDataLine	POP H
0636	F7		RST PushNextWord
PushNextWord has pushed the address of the next line on the stack, but it has also left this address in BC. Here we test to see if this address is null (ie the null line at the end of the program has been reached) and if so then 'Out of Data' (OD) error.
0637	79		MOV A,C
0638	B0		ORA B
0639	1E06		MVI E,06
063B	CAD501		JZ Error
Get the first character of the line. If it's not the DATA keyword ID then loop back to try the next line.
063E	23		INX H
063F	D7		RST NextChar
0640	FE83		CPI KWID_DATA
0642	C23506		JNZ NextDataLine
Found a DATA line. We remove the prog ptr to the beginning of the line from the stack (we don't need it - we have the ptr in HL) and jump up to GotDataItem.
0645	C1		POP B
0646	C32006		JMP GotDataItem