How to represent tuples in AST?

[Frederic_Loyer]

No, type:

# # (1,(2,3));;
- : int * (int * int) = (1, (2, 3))
# ((1,2),3);;
- : (int * int) * int = ((1, 2), 3)
# (1,2,3);;
- : int * int * int = (1, 2, 3)
# fst (1,2,3)
Error: This expression has type 'a * 'b * 'c
       but an expression was expected of type 'd * 'e

The 3 first tuples have different types. And the last expression shows that a 'a * 'b * 'c is not a pair. It can be compared to a structure with 3 fields. (I guess the memory representation is similar).

| PExp_tuple of expression list is done in the compiler, but this representation allows empty and singleton tuples. i.e. the single value could have multiple representations which doesn’t look algebraic, and will lead to extra code to handle invariants

Yes, such a representation will permit 0-tuples or 1-tuples. But the idea is to have a grammar which doesn’t permit it. Something like this tuples := expr ( ',' expr )+. (Adapt it to your prefered grammar compiler). Then, in OCaml, you won’t be able to have such tuples. (42) can’t be interpreted as a tuple.