Compilation as a Typed EDSL-to-EDSL Transformation

This article is about an implementation and compilation technique that is used in RAW-Feldspar which is a complete rewrite of the Feldspar embedded domain-specific language (EDSL) (Axelsson et al. 2010). Feldspar is high-level functional language that generates efficient C code to run on embedded targets. The gist of the technique presented in this post is the following: rather writing a back end that converts pure Feldspar expressions directly to C, we translate them to a low-level monadic EDSL. From the low-level EDSL, C code is then generated. This approach has several advantages: 1. The translation is simpler to write than a complete C back end. 2. The translation is between two typed EDSLs, which rules out many potential errors. 3. The low-level EDSL is reusable and can be shared between several high-level EDSLs. Although the article contains a lot of code, most of it is in fact reusable. As mentioned in Discussion, we can write the same implementation in less than 50 lines of code using generic libraries that we have developed to support Feldspar.