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Date: Thu, 22 Nov 2012 11:29:08 +0100
From: Jean-vincent.Loddo@lipn.univ-paris13.fr
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Subject: [Caml-list] Lazyness and exceptions

Hello,

I have observed a strange behaviour of lazy values when an exception is 
raised. Here a minimal code that reproduces the behaviour:

# let action =
     let thunk () =
       Printf.printf "aaa\n";
       failwith "bbb"
     in
     lazy (thunk ());;

val action : unit lazy_t = <lazy>

# Lazy.force action ;;
aaa
Exception: Failure "bbb".

# Lazy.force action ;;
Exception: Failure "bbb".

The lazy value seems to be (correctly) not re-evaluated but the 
exception is (strangely) raised again. Why does this happen?
Jean-Vincent Loddo