automatic concatenation

[Bill Allombert <allomber@math.u-bordeaux.fr>]

Hello pari-dev,

Trying to teach gp2c to handle automatic concatenation, I found
how weird it is in PARI.

The most striking example is

? x.V=[x]
? "a".V
%1 = ["a"]
? print("a".V)
a0.E-28V

because "a" are not parsed as expression in automatic concatenation 
context. So it is parsed as "a" . V, when . stand for 0.

The other example is
? a="A";
? print("A"[1])
A[1]
? print(a[1])
  ***   unexpected character: print(a[1])
                                     ^----
Cheers,

Bill