I think this is definitely a problem with a lot of functional code styles so when working functionally myself I try to be quite verbose and explicit within functions, spacing things out in recognizable patterns and using lets to capture intermediate computation steps.

I love side-effectless code, but I hate the assumption that side-effectless code is maximally perfect when on a single line - don't use variables for variable usages, use labeled pre-computations to clarify what you're actually doing to try and maintain readable self-documenting code.

(all that said, the example above is... sort of a weirdly terrible one like most string manipulation tasks are, string manipulation usually has a high ratio of computation to significant design decision making)