recursive types (and operations on them, like pretty-printing, comparison and unification) seem to be working.

big part of the code base still needs to be 'ported' to the updated type constructors.

structures/enum.js

@@ -17,7 +17,7 @@ export const enumType = variants => {
   }
   const [variant, ...rest] = variants;
   const variantType = getRight(variant);
-  return sumType(variantType)(enumType(rest));
+  return sumType(() => variantType)(() => enumType(rest));
 };
 
 const eatParameters = (numParams, result) => {