Partition into structures

1 files changed, 26 insertions, 0 deletions

diff --git a/general.sml b/general.sml
new file mode 100644
index 0000000..cde0514
--- /dev/null
+++ b/general.sml
@@ -0,0 +1,26 @@
+fun $ (x, y) = x y
+infixr 0 $
+
+fun printLn s = (print s; print "\n")
+
+fun lazy thunk =
+let
+  datatype 'a value =
+    Unevaluated of unit -> 'a |
+    Evaluated of 'a |
+    Exn of exn
+
+  val value = ref $ Unevaluated thunk 
+in
+  fn () =>
+    case !value of
+      Unevaluated th =>
+        let
+          val x = th () handle e => (value := Exn e; raise e)
+          val () = value := Evaluated x
+        in
+          x
+        end
+    | Evaluated v => v
+    | Exn e => raise e
+end