2008/9/10 Johannes Waldmann :

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Has there ever been a discussion of typed, user-definable, user-processable source code annotations for Haskell?

afair it was on haskell-prime list

http://hackage.haskell.org/trac/haskell-prime/ticket/88

if you can call that a discussion :-)

I had to implement a kind of annotation system for GHC as part of my Summer of Code project for compiler plugins. You can see a discussion at http://hackage.haskell.org/trac/ghc/wiki/Plugins/Annotations, though I was not aware of that Haskell' ticket. The system as I have implemented is quite basic: the absolute minimum I needed for plugins. The syntax is essentially: {-# ANN foo "I am an annotation!" #-} Where "I am an annotation" may be replaced with any Typeable value, and is subject to staging requirements analgous to Template Haskell (e.g. you may not refer to things in the module being compiled other than by Template Haskell Name). As well as values you can annotate types and modules, and annotations are accessible via the GHC API. See that wiki page for full details. This system has not yet been merged into GHC (or even code reviewed by GHC HQ), so if/when it becomes available to end users the design may have changed drastically. Cheres, Max