type source_position = {
  index: int,
  line: int,
  col: int,
};

type span = (source_position, source_position);
type spanning('a) = {
  item: 'a,
  span,
};

let origin = {index: 0, line: 0, col: 0};
let nopos = {index: (-1), line: (-1), col: (-1)};
let nospan = (nopos, nopos);

let advance_line = ({index, line, col: _}) => {
  index: index + 1,
  line: line + 1,
  col: 0,
};

let advance_col = ({index, line, col}) => {
  index: index + 1,
  line,
  col: col + 1,
};

let zero_width = (pos, item) => {span: (pos, pos), item};

let single_width = (pos, item) => {span: (pos, advance_col(pos)), item};

let start_end = (startPos, endPos, item) => {
  span: (startPos, endPos),
  item,
};

let replace = (span, item) => {span: span.span, item};

let map = (f, span) => {span: span.span, item: f(span.item)};

let start_pos = span => fst(span.span);
let end_pos = span => snd(span.span);

type ast_position = {
  pos_fname: string,
  pos_lnum: int,
  pos_bol: int,
  pos_cnum: int,
};

type ast_location = {
  loc_start: ast_position,
  loc_end: ast_position,
  loc_ghost: bool,
};