Generate NFAs from regexes

src/error.rs

@@ -2,10 +2,21 @@
 pub enum Error {
     GrammarError(String),
     SymbolError(String),
+    RegexError(String),
 }
 
 pub type Result<T> = std::result::Result<T, Error>;
 
+impl Error {
+    pub fn grammar(message: &str) -> Self {
+        Error::GrammarError(message.to_string())
+    }
+
+    pub fn regex(message: &str) -> Self {
+        Error::RegexError(message.to_string())
+    }
+}
+
 impl From<serde_json::Error> for Error {
     fn from(error: serde_json::Error) -> Self {
         Error::GrammarError(error.to_string())