(* hogeは int lazy_t 型 *)let hoge = lazy 1

$ cat test_ocaml.mllet hoge = lazy 1 + 2$ omake*** omake: reading OMakefiles*** omake: finished reading OMakefiles (0.01 sec)- build . test_ocaml.cmi+ ocamlfind ocamlopt -package oUnit -warn-error A -annot \ -I . -c test_ocaml.mlFile "test_ocaml.ml", line 1, characters 11-17:Error: This expression has type int lazy_t but an expression was expected of type int

let hoge = (lazy 1) + 2

(* hogeは int lazy_t 型 *)let hoge = lazy (1 + 2)

let rec map f s = lazy (match s with | (lazy SSnil) -> SSnil | (lazy (SScons(x, s))) -> SScons(f x, map f s))

$ cat test_ocaml.mllet hoge = lazy (1 + 2)

let _ = print_int (Lazy.force hoge)(* (Lazy.force hoge) は Int 型 *)$ ./test_ocaml3

$ cat test_ocaml.mllet hoge = lazy (1 + 2)

let _ = match hoge with | lazy i -> print_int i$ ./test_ocaml3

let plus (lazy m) (lazy n) = lazy (m + n)

let _ = let i = Lazy.force (plus (lazy 1) (lazy 2)) inprint_int i

fun lazy plus ($m, $n) = $m+n

fun plus (x, y) = $case (x, y) of ($m, $n) => force ($m+n)

(* plus : int lazy_t -> int lazy_t -> int lazy_t *)let plus m n = lazy(match (m, n) with | (lazy m, lazy n) -> m + n)

datatype a StreamCell = NIL | CONS of a * a Streamwithtype a Stream = a StreamCell susp

type 'a cell = SSnil | SScons of 'a * 'a streamand 'a stream = 'a cell Lazy.t

fun lazy ($NIL) ++ t = t | ($CONS (x, s)) ++ t = $CONS (x, s ++ t)

let rec (++) t1 t2 = lazy (match (t1, t2) with | (lazy SSnil, lazy t2) -> t2 | (lazy (SScons(x, s)), t2) -> SScons(x, s ++ t2))

fun lazy take (0, s) = $NIL | take (n, $NIL) = $NIL | take (n, $CONS (x, s)) = $CONS (x, take (n - 1, s))

let rec take n s = lazy (match (n, s) with | (0, _) -> SSnil | (_, lazy SSnil) -> SSnil | (n, lazy (SScons(x, s))) -> SScons(x, take (n - 1) s))

fun lazy drop (n, s) = let fun drop' (0, s) = s | drop' (n, $NIL) = $NIL | drop' (n, $CONS (x, s)) = drop' (n - 1, s) in drop' (n, s) end

let drop n s = lazy ( let rec drop' n s = match (n, s) with | (0, lazy s) -> s | (_, lazy SSnil) -> SSnil | (n, lazy (SScons(_, s))) -> drop' (n - 1) s in drop' n s)

fun lazy reverse s = let fun reverse' ($NIL, r) = r | reverse' ($CONS (x, s), r) = reverse' (s, $CONS (x, r)) in reverse' (s, $NIL) end

let reverse s = lazy ( let rec reverse' s r = match (s, r) with | (lazy SSnil, r) -> r | (lazy (SScons(x, s)), r) -> reverse' s (lazy (SScons(x, r))) in Lazy.force (reverse' s (lazy SSnil)))

https://github.com/master-q/\readPurelyFunctionalDataStructures/\tree/master/LazyEvaluation