Still trying to solve the same issue; getting the cost of movement to each tile on the map from the unit's current tile. Immediate neighbours would be a cost of 1 for grass tiles, 2 for the neighbours of neighbours etc. Some tiles would have increased cost, say forests might have a base cost of 2, so going through two forest tiles would cost 4.

Then gotta represent that as a highlighted area of possible moves.

I'll get that working eventually but for now I've just added a river to my demo map. (The highlighted area here is just for immediate neighbours, getting it to iterate correctly is proving difficult in a functional language :p)