A p_result type is what a parser will return after running. It takes types 'a and 'b where 'a is the type of the input that is being parsed, and 'b is the type of the output of your parsing.

The p_result type is constructed with either a Win constructor that holds a ('b * 'a) tuple or a Lose constructor that holds an error message.

The input and output types are both variable types in case you want to make your own parser with custom types!

There's also the PResultM monad which has a return function that wrapps its input in a Win constructor, and the bind (>>=) operator which applies a function to a p_result value if that value is a Win value.

The p_func type is the type signature for parser functions. Like p_result, it takes in types 'a and 'b where 'a is the type of the input and 'b is the type of the output.