Notes:

• You can type special characters with a backslash prefix, as shown by hovering over the character bar above. Documentation links for primitives are found here.
• Any modifier with enter will execute (not just shift).
• BQN uses ‿ (backslash-space) for stranding, and not juxtaposition. If you don't know what went wrong, check for this first!
• This implementation is still WIP, and in particular I am improving error checking and messages now. Support for function headers and multiple bodies is missing, and Under (⌾) only works for a small class of structural functions. Performance is bad.