Promoting energy efficiency to a first class system design goal is an important research challenge. Although more energy-efficient hardware can be designed, it is software that controls the hardware; for a given system the potential for energy savings is likely to be much greater at the higher levels of abstraction in the system stack. Thus the greatest savings are expected from energy-aware software development, which is the vision of the EU ENTRA project. This article presents the concept of energy transparency as a foundation for energyaware software development. We show how energy modelling of hardware is combined with static analysis to allow the programmer to understand the energy consumption of a program without executing it, thus enabling exploration of the design space taking energy into consideration. The paper concludes by summarising the current and future challenges identified in the ENTRA project.

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We present a simple way to implement typed abstract syntax for the lambda calculus in Haskell, using phantom types, and we specify normalization by evaluation (i.e., type-directed partial evaluation) to yield this typed abstract syntax. Proving that normalization by evaluation preserves types and yields normal forms then reduces to type-checking the specification.

We revisit Bondorf and Palsberg's compilation of actions using the offline syntax-directed partial evaluator Similix (FPCA'93, JFP'96), and we compare it in detail with using an online typedirected partial evaluator. In contrast to Similix, our typedirected partial evaluator is idempotent and requires no "bindingtime improvements." It also appears to consume about 7 times less space and to be about 28 times faster than Similix, and to yield residual programs that are perceptibly more efficient than those generated by Similix.

Macros still haven't made their way into typed higher-order programming languages such as Haskell and Standard ML. Therefore, to extend the expressiveness of Haskell or Standard ML, one must express new linguistic features in terms of functions that fit within the static type systems of these languages. This is particularly challenging when introducing features that span across multiple types and that bind variables. We address this challenge by developing, in a step by step manner, mechanisms for encoding patterns and pattern matching in Haskell in a type-safe way.