I think you're forgetting that the function can have more than one recursive call site within its body. A for-loop is identical to a recursive function contain

I think you're forgetting that the function can have more than one recursive call site within its body. A for-loop is identical to a recursive function containing only one call site within its body. By contrast, in order to calculate the number of nodes in a binary tree, you would do (nodes (tree) (if (tree? tree) (1+ (nodes (left-node tree)) (nodes (right-node tree))) 0)) which is not like a simple for loop at all.