Fixes identifier lexing; support REPL file loading

src/Lexer.hs

@@ -17,7 +17,9 @@ keywordT = string "t" *> notFollowedBy alphaNumChar *> pure LKeywordT
 
 identifier :: Lexer LToken
 identifier = do
-  name <- some (letterChar <|> char '_' <|> char '-')
+  first <- letterChar <|> char '_'
+  rest <- many (letterChar <|> char '_' <|> char '-' <|> digitChar)
+  let name = first : rest
   if (name == "t" || name == "__result")
     then fail "Keywords (`t`, `__result`) cannot be used as an identifier"
     else return (LIdentifier name)
@@ -31,11 +33,8 @@ stringLiteral :: Lexer LToken
 stringLiteral = do
   char '"'
   content <- many (noneOf ['"'])
-  if null content
-    then fail "Empty string literals are not allowed"
-    else do
-      char '"' --"
-      return (LStringLiteral content)
+  char '"' --"
+  return (LStringLiteral content)
 
 assign :: Lexer LToken
 assign = char '=' *> pure LAssign