Macros.md

Macros

syntax `if t `then a `else b =

match $t | True -> $a | False -> $b end

List literals are also defined with macros. Consider the following grammar definition:

list  = "[" "]" | items
items = expr | expr "," items

In Fold it can be encoded as:

syntax
  | `[ `] =
    `(List.empty)

  | `[ (x <- expr) (xs <- (`, expr)*) =
    `(List.prepend x xs)

The same grammar can be defined in the parser combinator style:

list = char '[' >> char ']' <|> char '[' >> items >> char ']'
items = do
  x  <- expr
  xs <- many (char ',' >> expr)
  return [x & xs]

if $cond then $e1 else $e2 =

case $cond of: True -> $e1 False -> $e2

factorial n =
if (n == 0) then:
  print "done"
  1
else:
  n * factorial (n - 1)

Modules

module Option
  type Self a = Some a | None

  def self ? default =
    match self
    | Some a -> a
    | None   -> default
    end

  include Monad.Make module
    type Self = Option.Self

    def pure = Some

    val bind f self =
      match self
      | Some a -> f a
      | None   -> None
      end
  end
end