benruijl/spl — comment on commit 0fc92d7636c2c95f670a7388efa80daae5595e08
File: Scanner.hs line 98
By benruijl:

It means: if not empty string. This is because you actually want the intScan to return Nothing on failure. If you enter "d2", it returns ("", "d2"). This is bad, because then the scanner seems to succeed.