Research area

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. The Expression Problem

In 1998 P.Wadler had defined "The Expresion Problem" (accordingly to Wouter Swierstra - Data types a la carte ).

"The goal is to define a data type by case, where one can add new cases to the data type and new functions over the dat a type , without recompiling existing code, and while retaining static type safety."

A new,simple and clear solution (2008) was given by Dan Popa in a speech scheduled for AngloHaskell/2008 You may download the presentation from

Why this solution is so interesting and so new: - it did not use a fixpoint operator !! - it did not use a Maybe (high level embeded) type !! - it did not use data declaration anymore !! - it is introducing pseudoconstructors over monadic values because the chain of unevaluated (yet) functions is actually forming a datastructure . do not forget that Haskell is a lazy evaluation language !!

Why this solution is valuable: - because we have already built modular languages like Rodin using it. - because it works with just a bit overloading of the system : See final pages of - because it is modular - because language construction tools are valuable software (1000$ a Licence for a good language generator.) - because it fits in the previous kind of systems with truee small modifications (just replace a single letter of a data constructor to transform it in a pseudoconstructor ...) - because my Ph.D Superviser is wishing to sell custom languages with a price of aprox 10 000$ / language - or at least he declared this some times ago.

References: see the .pdf of the latest papers from User:Ha$kell's homepage. Ill be back. Download and read the latest papers of Dan Popa from User:Ha$kell's homepage.

. Classic complex solutions

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. Monadic Interpretation

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. References

. Lucrarile publicate in 2008

Dan Popa, "Modular evaluation and interpreters using monads and type classes in Haskell" , Studii si Cercetari Ştiinţifice, Seria Matematica, Univ. Bacău, (18) 2008. An Open Office (.sxw) file is available here: Download .sxw After loading the .sxw in the Open Office, press the PDF button from the toolbar to produce your own .pdf file. Or Official PDF of the paper for <DOWNLOAD> , having the following title:

Direct modular evaluation of expressions using the monads and type classes in Haskell by DAN V. POPA UNIVERSITATEA DIN BACĂU STUDII ŞI CERCETĂRI ŞTIINŢIFICE Seria: MATEMATICĂ Nr. 18 (2008), pag. 233 – 248

The paper is introducing Pseudoconstructors over monadic values as a way of building modular trees without data or Haskell extensions. Modular adaptable interpreters for extensible languages - like Rodin - become now easy to build, without the need of any Haskell extensions.

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. History of the domain

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