Abstract not found

Certain programs making use of monads need to perform recursion over the values of monadic actions. Although the do-notation of Haskell provides a convenient framework for monadic programming, it lacks the generality to support such recursive bindings. In this paper, we describe an enhanced translation schema for the donotation and its integration into Haskell. The new translation allows variables to be bound recursively, provided the underlying monad comes equipped with an appropriate fixed-point operator.

Recent work on recursion over the values of monadic actions resulted in the introduction of a family of fixed point operators, one for each di#erent kind of monadic e#ect. In the context of Haskell, the function fixIO is the corresponding operator for the IO monad. Unfortunately, both the IO monad and fixIO are language primitives in Haskell, i.e. they can not be defined within the language itself. Therefore, any attempt to formally reason about fixIO is futile without a precise semantics for computations in the IO monad. Quite recently, Peyton Jones introduced an operational semantics based on observable transitions as a method for reasoning about I/O in Haskell. Building on this work, we show how one can model fixIO as well, and we argue that it indeed belongs to the family of fixed point operators that enable monadic value recursion.