Haskell is also optionally typed now (at least with GHC 7.6.1)

[Hamish Mackenzie]

They got there in the opposite direction from Typescript and the Closure Compiler though.

http://hackage.haskell.org/trac/ghc/wiki/DeferErrorsToRuntime

Add the pragma {-# OPTIONS_GHC -fdefer-type-errors #-} to your source file and type errors will just be reduced to warnings at compile time.

I have asked for -fdefer-undefined-errors using the recently added "Holes" feature (SPJ seems to be in favour).

http://hackage.haskell.org/trac/ghc/ticket/5910

Hamish