ambiguity of `1./a` (real literal and infixOp)

Summary:

1./a is parsed as 1.0/a instead of 1 ./ a (where are a is a vector). This confused me a bit.

To avoid this ambiguity I would prefer to not allow 1. but enforce 1.0 as I would consider the latter more readable anyways. If you care to much about breaking existing code, please consider to have the parser issue a warning in this case.

Related: In the grammar in the manual the definitions of numeric_literal and real_literal are equivalent: (every numeric is real)

numeric_literal ::= integer_literal | real_literal
integer_literal ::= 0 | [1-9] [0-9] *
real_literal ::= integer_literal ?('.' [0-9] * ) ?exp_literal

I would prefer:
real_literal ::= integer_literal '.' [0-9] + ?exp_literal

Current Version:

rstan (Version 2.16.2, packaged: 2017-07-03 09:24:58 UTC, GitRev: 2e1f913d3ca3)

Start with the grammar in the manual, especially the numeric_literal and real_literal definitions, and trace how 1./a is interpreted relative to 1 ./ a. Done means the ambiguity is resolved by enforcing 1.0, warning on 1., or otherwise documenting and implementing a clear choice.