There are several projects that make the haskell type checker run on the fly (more or less) as code is entered in an editor. ghc-mod is one; hdevtools is anothe

There are several projects that make the haskell type checker run on the fly (more or less) as code is entered in an editor. ghc-mod is one; hdevtools is another; FP complete has a web based haskell editor with on the fly type checking too.