We present an approach to live programming in a two-dimensional grid of functions where all intermediate values are always visible and tangible. Arguments are chosen through selecting values, and indicated by layout, so all interaction is directly focused on the data being manipulated, while the provenance of each result is always manifest. While originally designed to work with concatenative, stack-based programs, this system enables a variety of composed pipelines and calculations to be created outside the limits of that paradigm.

By showing both functions and their argument and return values at once, the relationship between data items is clear, and between data and the transformation functions operating on it. By choosing functions to use by selecting the visible values to operate on, then picking a compatible function, it is possible to explore the possibilities available from the current data. By updating constant values, or replacing functions in situ, the programmer can cause flow-on effects that will immediately appear on screen.

This system enables live, exploratory, functional programming in an unconventional way, but exposes functionality on demand, without overwhelming the user with options. It can support both low-level primitive values and very high-level abstractions, in the same program if desired, and it enables experimental changes to be tested, extended, and reverted. Users with little programming experience are able to manipulate their data directly while creating a reproducible program for doing so. A fully working implementation is available on the web, and this essay highlights the functionality and affordances that make it tick.