A Systematic Translation of Guarded Recursive Data Types to Existential Types

Guarded recursive data types (GRDTs) are a new language feature which allows to type check the different branches of case expressions under different type assumptions. We observe that GRDTs are pretty close in their typing behavior to type classes with existential types (TCET). We give a translation scheme from GRDTs to TCET. The translation to TCET might be ambiguous in the sense that common implementations such as the Glasgow Haskell Compiler (GHC) fail to accept the translated program. Hence, we provide for another translation from TCET to existential types (ET) which is accepted by GHC. To achieve this goal we combine an existing constraint solving procedure with a novel proof term construction method.