STRING_IF -- conditional statement for strings

OPERATION = <string:1>	'SUM'	EQ | NE | INDEX
STRING_ARGUMENTS = <string:0>	''	arguments for string operation
THEN = <string:1>	'undefined'	statement when IF evaluates to T
ELSE = <string:1>	'undefined'	statement when IF evaluates to F

Description:

This command performs a conditional IF operation on two string arguments. The possible operations are equal (EQ), not equal (NE), and the FORTRAN index() function (INDEX), which returns true if there is `argument2' substring within `argument1'. If the condition is true, the command specified in the THEN variable is executed. Otherwise the command in the ELSE variable is executed. Typically, these commands are GO_TO statements.