Help with an R1C1 reference in a function

I am trying to reference the cell immediately to the left of a cell that contains this function:

=IF(RC[-1]="value","output", "")

or

=IF(EQUALS(RC[-1],"value"),"output","")

...and I can't figure out what is wrong. It seems simple enough, but, I'm not the brightest bulb on the string, so, your help is very welcome.