It depends a lot on your priorities between mastering a language/programming and having a successful product/service (ie. making money).
In any case you should figure out first what you want to build as the choice of tools will depend on it.
Also keep in mind that while functional programming may be fun, it may be simpler and faster to just slap some php onto some random webhost (even more so when validating an idea and getting feedback) :)
Also keep in mind that while functional programming may be fun, it may be simpler and faster to just slap some php onto some random webhost (even more so when validating an idea and getting feedback) :)