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defmodule ErrorMonad do | |
def return(x) do | |
{:ok, x} | |
end | |
def and_then(m, f) do | |
case m do | |
{:ok, v} -> f.(v) | |
err -> err | |
end | |
end | |
end | |
defmodule Main do | |
def addFive(x) do | |
{:ok, x + 5} | |
end | |
def parseInt(x) do | |
case Integer.parse(x) do | |
{num, _} -> {:ok, num} | |
:error -> {:err, "Could not parse: #{x}"} | |
_ -> {:err, "Unkown error in parseInt/1"} | |
end | |
rescue | |
e -> {:err, e} | |
end | |
end | |
5 | |
|> ErrorMonad.return | |
|> ErrorMonad.and_then(&Main.parseInt/1) | |
|> ErrorMonad.and_then(&Main.addFive/1) | |
|> IO.inspect | |
"abc" | |
|> ErrorMonad.return | |
|> ErrorMonad.and_then(&Main.parseInt/1) | |
|> ErrorMonad.and_then(&Main.addFive/1) | |
|> IO.inspect | |
"23" | |
|> ErrorMonad.return | |
|> ErrorMonad.and_then(&Main.parseInt/1) | |
|> ErrorMonad.and_then(&Main.addFive/1) | |
|> IO.inspect | |
# In Haskell you combine the `|>` and the `ErrorMonad.and_then` to form | |
# the `>>=` operator, so this example might look like the following pseudo | |
# code: | |
# "23" | |
# & ErrorMonad.return | |
# >>= Main.parseInt | |
# >>= Main.addFive | |
# >>= IO.inspect | |
# | |
# Note: In Haskell `&` is the same as `|>` |
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