Texas Instruments TI-83 Plus Manual page 119

Chapter 2: TI-83 Plus Specific Information
For example, parse the graph equation Y1 and store the answer in Y. Install an error
handler around the parsing and the storing routine to catch any errors. RET CA = 0 if
OK, else ret CA = 1.
;
;
;
; returns if no error
;
;
;
; come here if any error was detected
; error handler is removed when the error occurred
;
ErrorHan:
;
storit:
;
;
;
;
y1Name:
TI-83 Plus Developer Guide
LD HL,y1Name
RST rMov9ToOP1
AppOnErr ErrorHan
B_CALL ParseInp
B_CALL CkOP1Real
JR Z,storit
AppOffErr
B_CALL CleanAll
SCF
RET
B_CALL StoY
AppOffErr
B_CALL CleanAll
CP A
RET
DB EquObj, tVarEqu, tY1, 0
; OP1 = Y1 name
; error handler installed
; parse the equation
; check if RealObj
; if a RealObj, try to store to Y
; remove the error handler
; remove temps if any
; set CA flag to signal failure
; store to Y, ret if no error, else
; ErrorHan
; remove error handler
; remove temps if any
; CA = 0 for no error
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Third Release May 28, 2002