Thinking of something like Halide, which splits the program into a algorithm part and an execution schedule: there may be productive ways to factorize "one-text-file" programming conventions into multiple aspects written in different IDE modes.

Haskell's "do" notation always seems ripe for this. Write the non-pure aspects of your code in a more appropriate language, or any one of a choice of front-ends. The aesthetic of typographic code in a flat file is strong in the FP community, but "do" notation is not its finest hour.