Allow selecting tuple by integer indices

[chengluyu]

Changes

Syntax

Tuple indices in selection should matches regular expression 0|[1-9][0-9]. Records and record types now accept non-negative integers as field names (e.g., { 1: "Hello" }).

• Parser: Allow selecting tuple indices (e.g., x.0) and using non-negative integer fields in records.
• MLParser: Same as Parser. Also allow non-negative integer fields in record types (e.g., { 1: int }).
• NewLexer: Allow SELECT's name to be tuple indices.
• NewParser: Same as Parser.

Typing

• TyperDatatypes: Update TupleType's toRecord methods.
• TypeSimplifier: Update the code that simplify tuple types.
• Typer: Update the code which treats Array as a supertype of tuple types.
• Typer: Fields that are integers or start with an underscore are not used as name hints.

JavaScript Code Generation

• Do not enclose field names in quotes if they are integers.

Tests

• Test cases: replace ._n to .(n-1).
• [x] I have meticulously read and reviewed the changes in DiffTests.

[LPTK]

Cool, thanks, but why on Earth would you update Parser and MLParser with that change? These are legacy parsers, and in particular we should get rid of Parser ASAP.

[chengluyu]

I have modified TupleType, so tests using the old parsers will also fail. So, I updated them as well.

[LPTK]

Why not mark the PR as "ready for review"?

[chengluyu]

Sorry, I forgot this time.

[chengluyu]

Thanks!