module Space_safe_tuple:The raison d'etre for Space_safe_tuple<N> is that OCaml doesn't properly free variables matched in tuple patterns. If one writessig..end
let (a, b) = ... in ... a ... b ...
when a and b appear at most once in the subsequent expression then this effectively becomes
let t = ... in ... (fst t) ... (snd t) ...
Hence, references to a and b keep alive the entire tuple. This can
lead to surprising space leaks.
One notable instance of this bad behaviour is when one writes:
let _,a = ... in ...a...
The first element of the tuple, albeit not even being named, is live in the subsequent expression.
By using Space_safe_tuple<N>, one makes it clear to the user where the tuple selection happens, and (hopefully) causes them to think about space safety, and to write the following if they want to free the tuple.
let t = ... in
let a = Space_safe_tuple2.get1 t in
let b = Space_safe_tuple2.get2 t in
... a ... b ...
module T2:sig..end
module T3:sig..end