package pretty_expressive

The pretty printer and document combinators, parameterized by a cost factory.

This functor is similar to Make, but it provides operators that are compatible with the paper. Using open on it will shadow built-in identifiers.

The default cost factory, parameterized by the page width limit page_width, and optionally the computation width limit computation_width. When the computation width limit is not specified, it is set to 1.2 * page_width.

In this cost factory, the cost type t is a pair of natural numbers, where the first component is badness, which is roughly speaking the sum of squared overflows, and the second component is the height (number of newlines).

Internally, default_cost_factory is defined as:

let default_cost_factory ~page_width ?computation_width () =
  (module struct
    type t = int * int
    let limit = match computation_width with
      | None -> (float_of_int page_width) *. 1.2 |> int_of_float
      | Some computation_width -> computation_width

    let text pos len =
      let stop = pos + len in
      if stop > page_width then
        let maxwc = max page_width pos in
        let a = maxwc - page_width in
        let b = stop - maxwc in
        (b * (2*a + b), 0)
      else
        (0, 0)

    let newline _ = (0, 1)

    let combine (o1, h1) (o2, h2) =
      (o1 + o2, h1 + h2)

    let le (o1, h1) (o2, h2) =
      if o1 = o2 then h1 <= h2 else o1 < o2

    let debug (o, h) = Printf.sprintf "(%d %d)" o h

  end: Signature.CostFactory with type t = int * int)