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(*
* This is based on
* Functional Unparsing
* BRICS Technical Report RS 98-12
* Olivier Danvy, May 1998
*)
signature FORMAT =
sig
type ('a, 'b) t
val eol: ('a, 'a) t
val format: (string, 'a) t -> 'a
val int: ('a, int -> 'a) t
val list: ('a, 'b -> 'a) t -> ('a, 'b list -> 'a) t
val lit: string -> ('a, 'a) t
val new: ('b -> string) -> ('a, 'b -> 'a) t
val o: ('a, 'b) t * ('c, 'a) t -> ('c, 'b) t
val string: ('a, string -> 'a) t
end
structure Format:> FORMAT =
struct
type ('a, 'b) t = (string list -> 'a) * string list -> 'b
val new: ('b -> string) -> ('a, 'b -> 'a) t =
fn toString => fn (k, ss) => fn b => k (toString b :: ss)
val lit: string -> ('a, 'a) t = fn s => fn (k, ss) => k (s :: ss)
val eol: ('a, 'a) t = fn z => lit "\n" z
val format: (string, 'a) t -> 'a = fn f => f (concat o rev, [])
val int: ('a, int -> 'a) t = fn z => new Int.toString z
val list: ('a, 'b -> 'a) t -> ('a, 'b list -> 'a) t =
fn f => fn (k, ss) =>
fn [] => k ("[]" :: ss)
| x :: xs =>
let
fun loop xs ss =
case xs of
[] => k ("]" :: ss)
| x :: xs => f (loop xs, ", " :: ss) x
in f (loop xs, "[" :: ss) x
end
val op o: ('a, 'b) t * ('c, 'a) t -> ('c, 'b) t =
fn (f, g) => fn (k, ss) => f (fn ss => g (k, ss), ss)
val string: ('a, string -> 'a) t = fn z => new (fn s => s) z
end
open Format
val _ =
if
"abc" = format (lit "abc")
andalso "abc" = format string "abc"
andalso "abc" = format (lit "a" o lit "b" o lit "c")
andalso "abc" = format (string o string o string) "a" "b" "c"
andalso "[a, b, c]" = format (list string) ["a", "b", "c"]
andalso "[1, 2, 3]" = format (list int) [1, 2, 3]
then ()
else raise Fail "bug"
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