ERROR

Syntax CATCH "ERROR

Explanation

ERROR is the error object used by the error handling mechanism. See also CATCH and THROW.

When you catch an error, the system variable ERROR contains a short word describing the error that occured. This variable is only set when a procedure is running. At toplevel, the variable contains the empty list []. Use these values to throw certain types of runtime errors.

SYNTAX Syntax error

BREAK The user clicked the yellow light

STOP The user clicked the red light. Same as TOPLEVEL, but prints the message Stopped!

TOPLEVEL Thrown by the TOPLEVEL command; returns to toplevel.

ACCESS A name or a procedure does not exist

CONVERSION Data conversion error

INPUT Missing inputs to a procedure

OUTPUT A procedure did not output anything

RESULT Unexpected result

BADPROC Malformed procedure definition

BADFORMAL Bad formal argument list

RUNTIME General runtime error

NAME A name is already being used

RECURSION Too many active procedures

MATH Math error

IO I/O error

COMMAND This command is only valid at toplevel

COMPONENT A component is outside the window

The system variable ERRORTEXT contains the text which Logo would otherwise have printed. This variable is only set when a procedure is running. At toplevel, the variable contains the empty list [].

Examples HELLO
HELLO is neither a procedure nor a name
TO CATCH.ERROR
CATCH "ERROR [HELLO]
PRINT LIST "|Code: | :ERROR
PRINT LIST "|Text: | :ERRORTEXT END CATCH.ERROR defined. CATCH.ERROR Code: ACCESS Text: HELLO is neither a procedure nor a name