Lazy Imperative Programming

In this paper we argue for the importance of lazy state, that is, sequences of imperative (destructive) actions in which the actions are delayed until their results are required. This enables state-based computations to take advantage of the control power of lazy evaluation. We provide some examples of its use, and describe an implementation within Glasgow Haskell. 1 Introduction There has long been a tension between functional programming languages and their more traditional imperative counterparts. On the one hand, functional languages are commonly more expressive and easier to reason about than imperative languages, but on the other hand, certain algorithms and interactions seem to rely fundamentally on state-based computation. It is clearly worth attempting to combine the strengths of each. Some languages like Scheme and ML have incorporated imperative actions as side effects. This approach only makes sense in a call-by-value language where the order of evaluation is statically de..