gistfile1.vim

let g:Maybe = {"v": []}

function! g:MaybeReturn(v)
  let maybe = deepcopy(g:Maybe)
  let maybe.v = [a:v]
  return maybe
endfunction

function! Just(x)
  return MaybeReturn(a:x)
endfunction

function! Nothing()
  let maybe = deepcopy(g:Maybe)
  let maybe.v = []
  return maybe
endfunction

function! g:Maybe.bind(F)
  if len(self.v) ==# 1
    let [x] = self.v
    return a:F(x)
  else
    return Nothing()
  endif
endfunction

function! GetMaybe1(a)
  if a:a % 2 ==# 0
    return Just(a:a)
  else
    return Nothing()
  endif
endfunction

function! GetMaybe2(a)
  if a:a % 3 ==# 0
    return Just(a:a)
  else
    return Nothing()
  endif
endfunction

echo MaybeReturn(6).bind(lambda('return GetMaybe1(a:1)')).bind(lambda('return GetMaybe2(a:1)'))