A compiler plugin that improves on the scala compiler on the assumption that the user is using the Scalazzi-safe subset of Scala.

• Sufficiency checker. Example.
• Non-ambigious typeclass resolution. Example.
• Orphan instance checker. Some examples.
• Polymorphic function optimization.

See test/files for more examples. We would like to get a lot more things done eventually, see open issues.

• No null.
• No catching exceptions in pure code.
• No type casing (isInstanceOf).
• No type casting (asInstanceOf).
• No side-effects.
• No equals, toString, hashCode.
• No notify or wait in pure code.
• No .getClass.

We are more interested in Scalazzi+, which adds:

• Only total functions.
• Eq (used in laws and pattern matching) must satisfy:
  • Identity of indiscernibles (indiscernible values are equal).
  • Indiscernibility of identicals (equal values are indiscernible from each other).

The last requirement might seem a bit cryptic, but it has a wide range of implications, for example:

if (a === b) {
  // now we know that a.type === b.type
}

• Better monadic comprehensions.
• Automatic typeclass derivation.
• Newtypes.
• Automatic code generation for Scala functions and expressions via the Curry-Howard isomorphism.
• Mutual tail recursion.