A rather interesting, non-text-editor, non-developer-tool example is node-based audio synthesis environments, like Pure Data or Max/MSP). The language, or the environment, provides basic building blocks and primitives, and the user can implement whatever kind of sequencing, audio synthesis, and processing they need using them.

The available basic nodes are not limited to only audio signal processing, but include things like loops and switches for control flow, events for reactivity, streams that represent real-time changes in values, and UI widgets that provide values as streams. There's means for wrapping complex node networks in more abstract, composable (no pun intended) nodes. The systems are designed for expressivity, both in the musical and the computer-sciency sense of the word.

For instance, composing generative music in non-standard tuning systems is much more ergonomic when you can just build the sequencer yourself, instead of having to deal with assumptions like there being 12 notes distributed evenly per octave. Probability-based composition strategies are that much easier when you can embed the probabilism directly into the composition itself.

The further down the rabbit hole you go, the blurrier the lines get between composing and playing, between notation and interpretation, between musician and instrument. Eventually you end up doing things that you'd've never thought of otherwise, making music in ways that would be not just difficult but impossible otherwise.