Add ENGLISH_GBNF to llama_grammar.py

Author: JamePeng

llama_cpp/llama_grammar.py

@@ -131,6 +131,15 @@ def from_json_schema(cls, json_schema: str, verbose: bool = True) -> "LlamaGramm
 ws ::= ([ \t\n] ws)?
 """
 
+ENGLISH_GBNF = r"""
+# note: this might be incomplete, mostly an example
+root        ::= en-char+ ([ \t\n] en-char+)*
+en-char     ::= letter | digit | punctuation
+letter      ::= [a-zA-Z]
+digit       ::= [0-9]
+punctuation ::= [!"#$%&'()*+,-./:;<=>?@[\\\]^_`{|}~]
+"""
+
 JAPANESE_GBNF = r"""
 root   ::= object
 value  ::= object | array | string | number | ("true" | "false" | "null") ws