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.

make_debug_format limit content is_tainted cost returns a debugging string containing these parameters.

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 quadruple of natural numbers.

• The first component is badness, which is roughly speaking the sum of squared overflows over the page width limit
• The second component is sum of overflows over a column separator.
• The third 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 * 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, 0)
      else
        (0, 0, 0)

    let newline _ = (0, 0, 1)

    let combine (o1, ot1, h1) (o2, ot2, h2) =
      (o1 + o2, ot1 + ot2, h1 + h2)

    let le c1 c2 = c1 <= c2

    let two_columns_overflow w = (0, w, 0)

    let two_columns_bias     _ = (0, 0, 0)

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

    let debug_format = make_debug_format page_width
  end: Signature.CostFactory with type t = int * int * int)