pub fn get_env() -> Map(String, String)

pub fn optional(
  env: Map(String, String),
  key: String,
  parser: fn(String) -> Result(a, b),
  fallback: a,
) -> a

pub fn required(
  env: Map(String, String),
  key: String,
  parser: fn(String) -> Result(a, b),
) -> Result(a, Nil)