[ferret_users] backquotes in qualifiers

[Ryo Furue <furue@xxxxxxxxxx>]

Hi Ferret developers and users,

This may have been already reported, but backquoted expressions seem
to confuse the parser:

  yes? set data coads_climatology
  yes? let dn = `sst,return=dsetnum`
   !-> DEFINE VARIABLE dn = 1
  yes? define axis/y=-90:90:3/unit=degree my_yax
  yes? define grid/like=sst[d=1]/y=my_yax grid1
  yes? define grid/like=sst[d=`dn`]/y=my_yax grid2
   **ERROR: command syntax: my_yax
  yes? let sst2 = sst[d=`dn`]
   !-> DEFINE VARIABLE sst2 = sst[d=1]
  yes? define grid/like=sst2/y=my_yax grid3

Ferret doesn't seem to like "sst[d=`dn`]" in 

   define grid/like=sst[d=`dn`]/y=my_yax grid2

As shown above, a workaround is to define an intermediate variable.

Hope this helps,
Ryo