anchor.diff:      width' d ^ fun w -> if p f w then t f else txt ^ spaces ^ f-w
   
     let fillBreak n d = mkFill (<) (flip nest linebreak) n d
  -  let fill n d = mkFill (<=) (K empty) n d
  +  let fill n d = mkFill (<=) (constant empty) n d
   
     let rec flatten doc = delay ^ fun () ->
       match doc with
  
positive.code:   let (langle,   rangle)   as lrangle   = (Text "<", Text ">")
    let (lbrace,   rbrace)   as lrbrace   = (Text "{", Text "}")
    let (lbracket, rbracket) as lrbracket = (Text "[", Text "]")
    let squote = Text "'"
    let lrsquote = (squote, squote)
    let dquote = Text "\""
  
negative.code: [<AutoOpen>]
  module Util =
    let inline (^) x = x
    let inline constant x _ = x
    let inline flip f x y = f y x
    let inline force (s: Lazy<_>) = s.Force ()
  
  