Source code may be found at https://github.com/ascandone/elm-lambda-interpreter

It seems to scroll forever. Does this example terminate? What would be an easier example to try?

  let Sub = λ a b f c.b (\ x.x True) (a (\ cc o.o cc (f (cc False))) (λ o.o c c)) False

See also https://tromp.github.io/blog/2023/11/24/largest-number

so easy to read, missed a comma in line 503