First off, well done.

My big issue with method chaining is exactly the one of requiring the line-continuation-escape, or enclosing the whole thing in parens. You also need to wrap the initial value, then possibly unwrap it at the end, and you're limited to the methods you define (mind you, this seems like a pretty comprehensive list).

For this reason I decided to emulate clojure's threading macros instead, as a pair of functions:

    pipe_{first,last}(
        init_val,
        some_unary_callable, # so far so familiar
        (some_n_ary_callable, *args), # puts the piped value first or last, depending on {first/last}
        ...
    )

Unfinished is the version that makes `(callable, ...args..., _, ...more_args...)` work, is that what you mean by the _ lambda operator?