Sine Expression along a curve

I’m new to grasshopper and got a bit stuck.
Essentially I’ve im trying to replace my graph mapper with a sine expression since galapagos doesnt work with the graph mapper. Since the graph mapper has an input and output, im struggling to figure out the imput for my expression. My graph mapper had an imput through a curve so is there a way to do the same with my expression. I added an image to show what my graph mapper is doing. (6.9 KB)

hope this explains / helps - kind regards -tom