Difference between revisions of "Generalised algebraic datatype"
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Revision as of 21:15, 25 March 2006
General
 A short descriptions on generalised algebraic datatypes here as GHC language features
 Another description with links on Haskell' wiki
Example
An example: it seems to me that generalised abstract datatypes can provide a nice solution to a problem described in Daan Leijen and Erik Meijer's paper (see PostScript version) on the original HaskellDB page: making typeful (safe) representation of terms of another language (here: SQL). In this example, the problem has been solved in a funny way with Phantom type (we destroy and rebuild, a nice topic for a myth or scifi where a dreamworld is simulated on top of a previously homogenized world to look like the original?), but solving the problem with GADTs seems to be a more direct way (maybe that's why Simple unificationbased type inference for GADTs mentions that they are also called as firstclass phantom types?)
Related concepts
There are other developed tricks with types in Type, and another way to a more general framework in Dependent types. The fully dependently typed langage's Epigram tutorial (section 6.1) mentions Haskells GADTs and Epigram's relatedness to Haskell achieved by them.
The more general problem (representing the terms of a language with the terms of another language) can develop surprising things, e.g. quines (selfreplicating or selfrepresenting programs) on Combinatory logic.