Use = rather than as for assigning column aliases in group and compute

[julianhyde]

Morel should use = rather than as for assigning column aliases. Morel already uses = in records but it currently uses as in group and compute clauses.

Using as is inconsistent with uses of = elsewhere, and will be confusing when we implement Standard ML layered patterns (e.g. val x as (fst,snd) = (2, true)).

Currently we would write

from e in emps,
    d in depts
  where e.deptno = d.deptno
  group e.id + d.deptno as x, e.deptno
    compute sum of e.id as sumId;

but this would become

from e in emps,
    d in depts
  where e.deptno = d.deptno
  group x = e.id + d.deptno, e.deptno
    compute sumId = sum of e.id;

If you want an expression with =, you should enclose in parentheses, e.g.

from e in emps
group parity = (e.id mod 2 = 1) compute c = count

This is no great hardship; there are only automatic aliases for variables and field references, and e.id mod 2 = 1 is an expression, so you would have had to provide an alias anyway.

[julianhyde]

Fixed in 9219191.