Errors

Parse Errors

These errors occur when the program list is formally incorrect. That prevents a program to be loaded into the runner.

Error	Description
EXTRA ARGUMENT	Parsing the arguments of an otherwise valid instruction, there are more characters in the line. Likely cause is that the final expression is correctly readable up to the point where there is an error; or a forgotten colon?
DUPLICATE LABEL	A label with the same name was already placed at a point before this.
REFERENCE EXPECTED	In an assignment (FOR, NEXT, LET, INPUT, READ, GET or PULL) instruction the argument does not conform the format of [Names].
DEF SYNTAX	In a DEF instruction, the name of the function does not conform the format of [Names].
SYNTAX	The instruction expects a certain symbol (equals sign, comma, parenthesis) or keyword (TO, STEP, THEN; GOTO/GOSUB after ON; or, abbreviation thereof) that is not found where expected.
PARSE	String literal's double quote missing its pair.
INSTRUCTION EXPECTED	The instruction should either start with the instruction keyword, or be formatted like an implicit LET assignment: name = expression.

Run Time Errors

Some errors occur when the program is already running.

Error	Description	Recovery in Failsafe Mode
NEXT WITHOUT FOR	Encountering a FOR instruction, the runner pushes a loop structure on the stack of loops. Encountering a NEXT, it pops. This error occurs when the stack is empty when the NEXT is encountered.	Program Restart
LOOP MISMATCH	NEXT instruction specified the name of the loop counter but on the loop stack top, a loop with a different counter is found.	Iterate the loop on the stack top
DIM OVERDEFINES DEF	At a DIM instruction: there is a function defined with the name of the array being defined here.	The name will refer to the function where applicable
OUT OF DATA	READ instruction tried to fetch the next item defined in the DATA instructions, but it passed the last item of the whole program.	Assign empty string
LABEL DOES NOT EXIST	GOTO, GOSUB or RESTORE instruction refers to a label that is nowhere placed using any @ instruction.	RESTORE: restore to starting position GOTO/GOSUB: Program Restart
NO DATA AT LABEL	RESTORE instruction refers to a label that is placed before some instruction other than DATA.	Restore to starting position
CALL MISMATCH	Each time the runner encounters GOSUB, it pushes the label in the argument to the stack. Here RETURN instruction specified a label that does not match the label on the top of the stack.	Return to the address on the top of the stack
RETURN WITHOUT GOSUB	RETURN instruction is encountered when the stack is empty. May well have been emptied by an extra RETURN or a PULL instruction.	Program Restart
DEF OVERDEFINES DIM	At a DEF instruction: there is an array defined with the name of the function being defined here.	The name will refer to the function where applicable
DIVIDE BY ZERO	/ or MOD operator encountered with a value equal to 0 on the argument stack top	/ operator: evaluates to Number.MAX_VALUE MOD: evaluates to empty string
ILLEGAL EXPRESSION	In the process of evaluating an expression, the JavaScript implementation of a calculation returns the NaN value as the intermediate result.	Evaluate to empty string
NO VALUE	Evaluating a reference to a variable, by that name none is initialized. Or, evaluating a reference to an array element when no array by that name is defined, or element not initialized.	Evaluate to empty string
INVALID REFERENCE	In assignment (FOR, NEXT, LET, implicit LET, INPUT, READ, GET or PULL) the reference was neither a variable nor an array element. Often because it is a function.	Forget the value and run on

Failsafe Mode

While programming, error messages are essential information. The program better stops running as soon as possible if an error occurs, so the programmer can tell where the root cause is - and correct the program there. This is called debug mode or failfast mode.

But when a user who is not familiar with the program design sees those error messages, they can do little with it. Therefore there is a failsafe mode, in which there are no run time error messages, the program keeps recovering from errors.

The failsafe mode will be effective when you download your program from the Misc. tab and publish it.