whisper : add grammar-based sampling (#1229)

* whisper : add grammar-based sampling

* build : fix after master merge

* command : fix exception when recognizing the command

* whisper : fine-tuning grammar functionality

* command : grammar-related improvements

- option to read grammar from file
- add sample grammars for colors and chess moves
- fine-tune the performance further

* grammars : add assistant + update comments

* command : enable beam-search, add "no_timestamps", add "context", add p

* whisper : remove comment

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

examples/grammar-parser.h

@@ -0,0 +1,29 @@
+// Implements a parser for an extended Backus-Naur form (BNF), producing the
+// binary context-free grammar format specified by whisper.h. Supports character
+// ranges, grouping, and repetition operators. As an example, a grammar for
+// arithmetic might look like:
+//
+// root  ::= expr
+// expr  ::= term ([-+*/] term)*
+// term  ::= num | "(" space expr ")" space
+// num   ::= [0-9]+ space
+// space ::= [ \t\n]*
+
+#pragma once
+#include "whisper.h"
+#include <vector>
+#include <map>
+#include <cstdint>
+#include <string>
+
+namespace grammar_parser {
+    struct parse_state {
+        std::map<std::string, uint32_t>                   symbol_ids;
+        std::vector<std::vector<whisper_grammar_element>> rules;
+
+        std::vector<const whisper_grammar_element *>      c_rules() const;
+    };
+
+    parse_state parse(const char * src);
+    void print_grammar(FILE * file, const parse_state & state);
+}