List of Expression Return Codes
One of the following values:
EXPR_NORMAL
No problems, expression evaluated successfully.
EXPR_INST_OVERFLOW
Expression caused an instruction stack overflow during parsing.
EXPR_UNKNOWN_TOKEN
Unknown function, constant, or register found during parsing.
EXPR_TOO_MANY_VARS
Expression caused a value stack overflow.
EXPR_TOO_MANY_REGS
Register array overflow, or register number too big.
EXPR_CANT_EVAL
Function can't be evaluated with given arguments.
EXPR_CANT_PARSE
Expression can't be parsed syntactically.