User Definable Desugaring

• Allow some specification of a desugaring tool in a meta file to apply to concrete syntax
• Make it easier to add custom desugarings (use meta file?), maybe implement extra desugaring for concat*string (use &?)
• Let the Stratego compiler not desugar the AST of a concrete syntax section with the Stratego desugaring rules.
• Depending on the desugaring solution and the location of MetaExplode in the pipeline, MetaExplode should double quote strings. Also lists should be represented in the same way as they are represented after parsing.