Unboxed type: Difference between revisions
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#See the [http://www.haskell.org/ghc/docs/latest/html/users_guide/primitives.html discussion on primitives] in the [http://www.haskell.org/ghc/docs/latest/html/users_guide/users-guide.html GHC's User's Guide]. | #See the [http://www.haskell.org/ghc/docs/latest/html/users_guide/primitives.html discussion on primitives] in the [http://www.haskell.org/ghc/docs/latest/html/users_guide/users-guide.html GHC's User's Guide]. | ||
#See the [http://haskell. | #See the [http://www.haskell.org/ghc/docs/latest/html/libraries/base/GHC-Exts.html GHC.Exts] module. | ||
#See SPJ's paper [http://research.microsoft.com/Users/simonpj/Papers/unboxed-values.ps.Z Unboxed values as first class citizens]. | #See SPJ's paper [http://research.microsoft.com/Users/simonpj/Papers/unboxed-values.ps.Z Unboxed values as first class citizens]. | ||
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This page is a work in progress by IsaacJones. More input welcome :) | This page is a work in progress by IsaacJones. More input welcome :) | ||
Revision as of 23:38, 23 August 2007
Unboxed types are types that represent raw values. Unboxed types have kind #.
Note that unboxed types of different storage behaviours (four bytes, eight bytes etc.) are all lumped together under kind #. As a result, type variables must have kinds which are #-free.
From the old Wiki
One might imagine numbers naively represented in Haskell "as pointer to a heap-allocated object which is either an unevaluated closure or is a "box" containing the number's actual value, which has now overwritten the closure" [3. below]. GHC (and other implementations?) allow direct access to the value inside the box, or "Unboxed" values.
In GHC, by convention(?), unboxed values have a hash mark as a suffix to their name. For instance, the unboxed reprsentation of 42 is 42#. There are some restrictions to their use. In particular, you can't pass them to polymorphic functions (like show for instance).
In this example, I# is a constructor that takes an unboxed integer and returns the Int that we know and love.
module Main where
import GHC.Exts
showUnboxedInt :: Int# -> String
showUnboxedInt n = (show $ I# n) ++ "#"Here we wrap the unboxed Int n with the I# constructor and show the regular-old Int, whith a hash mark on the end.
Unboxed Tuples and Arrays
...
When to use Unboxed Types
...
See Also
- See the discussion on primitives in the GHC's User's Guide.
- See the GHC.Exts module.
- See SPJ's paper Unboxed values as first class citizens.
This page is a work in progress by IsaacJones. More input welcome :)