Script to generate domain-specific Elm types wrapping primitives (see https://robots.thoughtbot.com/lessons-learned-avoiding-primitives-in-elm for why this is a good idea)

README.md

Script to generate domain-specific Elm types wrapping primitives (see https://robots.thoughtbot.com/lessons-learned-avoiding-primitives-in-elm for why this is a good idea)

Use looks like:

% ./create_newtype Email String > email.elm

module Email exposing (Email, fromString, toString, map, map2)

type Email = Email String

fromString : String -> Email
fromString x =
  Email x

toString : Email -> String
toString (Email x) =
  x

map : (String -> String) -> Email -> Email
map f (Email x) =
  Email (f x)

map2 : (String -> String -> String) -> Email -> Email -> Email
map2 f (Email x) (Email y) =
  Email (f x y)

create_newtype

#!/usr/bin/env ruby

newtype = ARGV[0]
wrapped_type = ARGV[1]

text = <<-TXT
module #{newtype} exposing (#{newtype}, from#{wrapped_type}, to#{wrapped_type}, map, map2)

type #{newtype} = #{newtype} #{wrapped_type}

from#{wrapped_type} : #{wrapped_type} -> #{newtype}
from#{wrapped_type} x =
  #{newtype} x

to#{wrapped_type} : #{newtype} -> #{wrapped_type}
to#{wrapped_type} (#{newtype} x) =
  x

map : (#{wrapped_type} -> #{wrapped_type}) -> #{newtype} -> #{newtype}
map f (#{newtype} x) =
  #{newtype} (f x)

map2 : (#{wrapped_type} -> #{wrapped_type} -> #{wrapped_type}) -> #{newtype} -> #{newtype} -> #{newtype}
map2 f (#{newtype} x) (#{newtype} y) =
  #{newtype} (f x y)
TXT

puts text