Fix examples

[dagit]

Thanks for making this package. I wanted to try out the examples and noticed that two of them didn't compile:

• Type error in Expr2.hs. It looks like symbol was renamed to token but the Expr2 example already defined a function locally named token and so it was getting mysterious looking type errors. Renaming the local definition to tok and updating the uses fixed the problem.
• No Main module in Infinite.hs. An explicit module name was given, so I just removed it. With the explicit module name ghc was refusing to generate the binary so cabal install -fexamples was failing to find the early-infinite binary and erroring out as a result.

[ollef]

Drat! I could have sworn I tested the examples, but apparently that's not true.

Many thanks for fixing this! :)