SI-8044 Allow binding backquoted varid in patterns

Previously, a varid could not be backquoted, so that it was not
possible to introduce variables with names such as `type` in a
match expression.

This commit allows backquoted varids in `case x @ _` and
`case x: Int`. In neither position is a stable id accepted,
that is, an id with leading uppercase.

Therefore, this commit merely relaxes the backquoted varid to
be taken as a normal varid in these contexts.

2 files changed, 4 insertions, 2 deletions

diff --git a/spec/01-lexical-syntax.md b/spec/01-lexical-syntax.md
index 0232ed9a34..4e92c7cf7b 100644
--- a/spec/01-lexical-syntax.md
+++ b/spec/01-lexical-syntax.md
@@ -49,6 +49,8 @@ classes (Unicode general category given in parentheses):
 ```ebnf
 op       ::=  opchar {opchar}
 varid    ::=  lower idrest
+boundvarid ::=  varid
+             | ‘`’ varid ‘`’
 plainid  ::=  upper idrest
            |  varid
            |  op
diff --git a/spec/08-pattern-matching.md b/spec/08-pattern-matching.md
index 3b481eea86..6753fa3ec7 100644
--- a/spec/08-pattern-matching.md
+++ b/spec/08-pattern-matching.md
@@ -10,10 +10,10 @@ chapter: 8
 
 ```ebnf
   Pattern         ::=  Pattern1 { ‘|’ Pattern1 }
-  Pattern1        ::=  varid ‘:’ TypePat
+  Pattern1        ::=  boundvarid ‘:’ TypePat
                     |  ‘_’ ‘:’ TypePat
                     |  Pattern2
-  Pattern2        ::=  varid [‘@’ Pattern3]
+  Pattern2        ::=  boundvarid [‘@’ Pattern3]
                     |  Pattern3
   Pattern3        ::=  SimplePattern
                     |  SimplePattern {id [nl] SimplePattern}