`super` in Bash

gistfile1.sh

#!/usr/bin/env bash

source super.bash

foo() {
  echo hello
}
super_function foo

foo() {
  super
  echo world
}
super_function foo

foo   # prints "hello\nworld"

super.bash

is_function() {
  [ "$(type -t "$1" || true)" = "function" ]
}

function_body() {
  local name="$1"
  if is_function "$name"; then
    local body="$(declare -f "$name")"
    body="${body#*{}"
    echo "${body%\}}"
  else
    echo "no such function \`$name'" >&2
    return 1
  fi
}

define_function() {
  local name="$1"
  local body="$2"
  eval "${name}() { ${body}; }"
}

alias_function() {
  local src="$1"
  local dst="$2"
  define_function "$dst" "$(function_body "$src")"
}

rename_function() {
  local src="$1"
  local dst="$2"
  alias_function "$src" "$dst"
  unset -f "$src"
}

chain_function() {
  local name="$1"
  local prefix="$2"
  local prefix_name="${prefix}${name}"

  if is_function "$prefix_name"; then
    chain_function "$prefix_name" "$prefix"
  fi
  rename_function "$name" "$prefix_name"
}

super_function() {
  local name="$1"
  local body="$(function_body "$name")"

  local wrapped_body='
    local __last_super_function="$__super_function"
    __super_function="__super_$FUNCNAME"
    local __super_result=0
    {'"$body"';} || __super_result="$?"
    __super_function="$__last_super_function"
    return "$__super_result"'

  if ! is_function "__super_$name"; then
    define_function "__super_$name" 'echo "super: superfunction not found" >&2; return 1'
  fi

  chain_function "$name" __super_
  define_function "__super_$name" "$wrapped_body"
  define_function "$name" '"__super_$FUNCNAME" "$@"'
}

super() {
  if is_function "$__super_function"; then
    "$__super_function" "$@"
  else
    echo "super: must be called from inside a superfunction" >&2
    return 1
  fi
}