The [`int` regular expression](https://github.com/realworldocaml/examples/blob/master/code/parsing/lexer.mll#L16) is probably better written as `['0'-'9']+` rather than `['0'-'9'] ['0'-'9']*`.
The
intregular expression is probably better written as['0'-'9']+rather than['0'-'9'] ['0'-'9']*.