wiki:FunctionalDependencies

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Functional Dependencies

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See ExtensionDescriptionHowto for information on how to write these extension descriptions. Please add any new extensions to the list of HaskellExtensions.

Brief Explanation

References

Pros

  • In GHC and Hugs for a long time.

Cons

  • Recently, some problems with FDs have been identified, see also the material on AssociatedTypes.
  • There are (at least) three different versions of FDs:
    1. Mark Jones' original proposal. Problem: It excludes some uses of FDs.
    2. GHC's implementation. Problem: It makes type checking undecidable. (See Duck et al. for an example.)
    3. Chameleon's implementation. Problem: Needs type inference based on constraint handling rules (not just HM). Doesn't support separate compilation atm.

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