ocamlのトレースでパラメータがと表示されるケース

昨日のような簡単な再帰関数だとトレース結果もわかりやすいので、もうちょっと複雑なクイックソートのトレースを見てみました。

let rec quick_sort lst =
  let take n lst p = List.filter (fun item -> p item n) lst 
  in let take_less n lst = take n lst (<)
     in let take_greater n lst = take n lst (>)
	in let take_equal n lst = take n lst (=)
	   in match lst with
	       [] -> [] 
	     | first :: rest -> quick_sort (take_less first rest)
	       @ take_equal first lst
	       @ quick_sort (take_greater first rest)

# #trace quick_sort;;
quick_sort is now traced.
# quick_sort [5; 4; 9; 8; 2; 3];;
quick_sort <-- [<poly>; <poly>; <poly>; <poly>; <poly>; <poly>]
quick_sort <-- [<poly>; <poly>]
quick_sort <-- []
quick_sort --> []
quick_sort <-- [<poly>]
quick_sort <-- []
quick_sort --> []
quick_sort <-- []
quick_sort --> []
quick_sort --> [<poly>]
quick_sort --> [<poly>; <poly>]
quick_sort <-- [<poly>; <poly>; <poly>]
quick_sort <-- []
quick_sort --> []
quick_sort <-- [<poly>; <poly>]
quick_sort <-- [<poly>]
quick_sort <-- []
quick_sort --> []
quick_sort <-- []
quick_sort --> []
quick_sort --> [<poly>]
quick_sort <-- []
quick_sort --> []
quick_sort --> [<poly>; <poly>]
quick_sort --> [<poly>; <poly>; <poly>]
quick_sort --> [<poly>; <poly>; <poly>; <poly>; <poly>; <poly>]
- : int list = [2; 3; 4; 5; 8; 9]

するとこんなふうにパラメータがと表示されて、何が渡されたのかよくわかりません。

多相関数だとこうなるみたいです。polyはpolymorphicの意味ですね。

局所定義しているtakeのパラメータnをintにしてみるとトレースがちゃんと表示されました。

let rec quick_sort lst =
  let take (n: int) lst p = List.filter (fun item -> p item n) lst 
  in let take_less n lst = take n lst (<)
     in let take_greater n lst = take n lst (>)
	in let take_equal n lst = take n lst (=)
	   in match lst with
	       [] -> [] 
	     | first :: rest -> quick_sort (take_less first rest)
	       @ take_equal first lst
	       @ quick_sort (take_greater first rest)

# #trace quick_sort;;
quick_sort is now traced.
# quick_sort [5; 4; 9; 8; 2; 3];;
quick_sort <-- [5; 4; 9; 8; 2; 3]
quick_sort <-- [9; 8]
quick_sort <-- []
quick_sort --> []
quick_sort <-- [8]
quick_sort <-- []
quick_sort --> []
quick_sort <-- []
quick_sort --> []
quick_sort --> [8]
quick_sort --> [8; 9]
quick_sort <-- [4; 2; 3]
quick_sort <-- []
quick_sort --> []
quick_sort <-- [2; 3]
quick_sort <-- [3]
quick_sort <-- []
quick_sort --> []
quick_sort <-- []
quick_sort --> []
quick_sort --> [3]
quick_sort <-- []
quick_sort --> []
quick_sort --> [2; 3]
quick_sort --> [2; 3; 4]
quick_sort --> [2; 3; 4; 5; 8; 9]
- : int list = [2; 3; 4; 5; 8; 9]

プログラミングの基礎 (Computer Science Library)

参考 : Debugging facilities in Caml