IMO it should be like Fennel and just support `lambda` and `λ`. The latter is not even that hard to type, in virtually any free (libre) OS you can just

    $ echo '
    <Multi_key> <Y> <Y> : "Λ" # GREEK CAPITAL LETTER LAMDA
    <Multi_key> <y> <y> : "λ" # GREEK CAPITAL LETTER LAMDA
    ' >> ~/.XCompose

If you’re limited by a nonfree OS you should be able to patch the problem with free duct tape like Karabiner or AutoHotKey.

And in vim you can just

    <C-K>*l

in insert mode (which can be done with option-l on macOS if you `inoremap ¬ <C-K>*l` https://apple.stackexchange.com/questions/230422/type-lambda...).