Fix lexing of names in R lexer (#896)

The R lexer does not properly lex names with digits. This commit fixes that.

lib/rouge/lexers/r.rb

@@ -60,16 +60,15 @@ def self.detect?(text)
         rule %r/%[^%]*?%/, Operator
 
         rule %r/0[xX][a-fA-F0-9]+([pP][0-9]+)?[Li]?/, Num::Hex
-        rule %r/[+-]?(\d+([.]\d+)?|[.]\d+)([eE][+-]?\d+)?[Li]?/,
-          Num
+        rule %r/[+-]?(\d+([.]\d+)?|[.]\d+)([eE][+-]?\d+)?[Li]?/, Num
 
         # Only recognize built-in functions when they are actually used as a
         # function call, i.e. followed by an opening parenthesis.
         # `Name::Builtin` would be more logical, but is usually not
         # highlighted specifically; thus use `Name::Function`.
         rule %r/\b(?<!.)(#{PRIMITIVE_FUNCTIONS.join('|')})(?=\()/, Name::Function
 
-        rule %r/[a-zA-Z.]([a-zA-Z_][\w.]*)?/ do |m|
+        rule %r/(?:(?:[[:alpha:]]|[.][._[:alpha:]])[._[:alnum:]]*)|[.]/ do |m|
           if KEYWORDS.include? m[0]
             token Keyword
           elsif KEYWORD_CONSTANTS.include? m[0]

spec/visual/samples/r

@@ -5,6 +5,8 @@
 
 ## Valid names
 abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUV0123456789._a <- NULL
+f2_bar <- NULL
+F2_BAR <- NULL
 .foo_ <- NULL
 ._foo <- NULL
 . <- NULL