Maybe.bash

Maybe::Just() {
  printf 'Maybe::Just(%s)' "${1}"
}

Maybe::Nothing() {
  printf 'Maybe::Nothing'
}

Maybe::map() {
  case "${2}" in
    'Maybe::Just('*')') Maybe::Just "$(${1} "$(args "${2}")")";;
    'Maybe::Nothing') Maybe::Nothing;;
  esac
}

ctor() {
  printf '%s' "${1%%\(*}"
}

args() {
  local args="${1#$(ctor "${1}")}"
  printf '%s' "${args:1:-1}"
}

inc() {
  printf $(($1 + 1))
}


if [[ ${BASH_SOURCE[0]} = ${0} ]]; then
  echo ' [in]: Maybe::map inc "$(Maybe::Just 10)"'
  printf '[out]: '
  Maybe::map inc "$(Maybe::Just 10)"
  echo
  echo

  printf ' [in]: '
  printf 'm=$(Maybe::Just 10)
  ...: mm=$(Maybe::Just ${m})
  ...: echo mm is "${mm}"
  ...: Maybe::map "Maybe::map inc" "${mm}"'

  echo
  echo
  echo '[out]: '
  m=$(Maybe::Just 10)
  mm=$(Maybe::Just ${m})

  echo mm is "${mm}"

  Maybe::map "Maybe::map inc" "${mm}"
  echo
fi