Allow parentheses to be omitted around tuples where sensible

[SheepTester]

In Python, you don't need parentheses around tuples all the time. For example,

# Swaps variables
a, b = b, a

# Iterate over list with index
for i, item in enumerate(list_of_items_):

# Return a tuple
return None, False

Currently, N requires parentheses around tuple expressions/literals and types (but not patterns, I think). So, currently, the programmer has to write

let a, b: (char, float) = (\{π}, 3.14)

I feel like those parentheses around the value and type annotation aren't necessary, so instead, one can just write

let a, b: char, float = \{π}, 3.14

Parentheses will still be required inside type variables, lists, function arguments, and other tuples:

let wow: list[(char, float)] = [(\{e}, 2.72), (\{π}, 3.14)]

print((1, (2, 3)))

so I don't think allowing their omission should cause any problems.

(I'm adding the Python label because it's not in the Python implementation but it is in the JS implementation as of now; if this feature request gets rejected then I'll have to fix the JS impl.)

[SheepTester]

To implement this, I think we can first rename expression to nontuple_expression, and then replace the mentions of expression in listval, etc. with nontuple_expression. Then, we can define expression to be either a nontuple_expression or a tupleval. We can then remove parentheses from tupleval. Because expression can also be boolean_expression, we probably should either require tupleval to have at least two items (changing * -> + should do that) or in scope.py check how many items there are before creating a tuple.

tupleval: nontuple_expression ("," nontuple_expression)+ (",")?
?nontuple_expression: ifelse_expr
           | boolean_expression
           | function_def
           | anonymous_func
           | function_callback_pipe
           | match
?expression: nontuple_expression
           | tupleval

And something similar for tuple types (tupledef).

We'd also have to relax the use of parentheses around tuples in the tests

[SheepTester]

Also, just to be safe, we should disallow a trailing comma unless it's inside parentheses

[Ashvin-Ranjan]

I think this is not that worth it for the number of edge cases it adds.

[SheepTester]

edge cases

Do you have any examples?

[Ashvin-Ranjan]

I still dislike this.