Historical question about backquote (`)

[Jon H. LaBadie]

I've been wondering about this for a number of years.
About time I asked the experts.

A long time ago I stumbled across some code that had
backquotes where forward quotes were intended for character
constants.  I would have expected the error message to
be something like:

	illegal character "`": line NNN

but to my surprise I got something like:

	illegal BCD constant: line NNN

or

	illegal gcos BCD constant: line NNN

I presume, but seek clarification, that at one time the designers
of C planned to include a BCD constant type in the language and
that the backquote was reserved for introducing this data type.

Can anyone clarify the reason for this vestigal message?

BTW  The compilers in question were System V.  I do not know if
     the same type of messages appear in commercial compilers.

-- 
Jon LaBadie
{att, princeton, bcr, attmail!auxnj}!jonlab!jon