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authorFacundo Domínguez <facundo.dominguez@tweag.io>2014-01-29 12:43:03 -0200
committerFacundo Domínguez <facundo.dominguez@tweag.io>2014-12-02 12:55:30 -0200
commit79c87c039c47be0baf7a6dd33ecf5434daa1501c (patch)
treed8d97a28d3989bf7848a5c3f8f6a4697de72fd5c /testsuite/tests/codeGen/should_run/CgStaticPointers.hs
parenta2c0a8dd15de2023e17078fa5f421ba581b3a5fa (diff)
downloadhaskell-wip/static-pointers.tar.gz
Implement -XStaticValues.wip/static-pointers
Contains contributions from Alexander Vershilov and Mathieu Boespflug. As proposed in [1], this extension introduces a new syntactic form `static e`, where `e :: a` can be any closed expression. The static form produces a value of type `StaticPtr a`, which works as a reference that programs can "dereference" to get the value of `e` back. References are like `Ptr`s, except that they are stable across invocations of a program. In essence the extension collects the arguments of the static form into a global static pointer table. The expressions can be looked up by a fingerprint computed from the package, the module and a fresh name given to the expression. For more details we refer to the users guide section contained in the patch. The extension is a contribution to the Cloud Haskell ecosystem (distributed-process and related), and thus has the potential to foster Haskell as a programming language for distributed systems. The immediate improvement brought by the extension is the elimination of remote tables from Cloud Haskell applications. Such applications contain table fragments spread throughout multiple modules and packages. Eliminating these fragments saves the programmer the burden required to construct and assemble the global remote table, a verbose and error-prone process, even with the help of Template Haskell, that moreover pollutes the export lists of all modules. [1] Jeff Epstein, Andrew P. Black, and Simon Peyton-Jones. Towards Haskell in the cloud. SIGPLAN Not., 46(12):118–129, September 2011. ISSN 0362-1340.
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diff --git a/testsuite/tests/codeGen/should_run/CgStaticPointers.hs b/testsuite/tests/codeGen/should_run/CgStaticPointers.hs
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+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE StaticPointers #-}
+
+-- |A test to load symbols produced by the static form.
+--
+-- First we have this program load itself using the GHC API.
+-- Then we look for the symbols that the static form should have
+-- exposed and use the values found at the symbol addresses.
+--
+module Main(main) where
+
+import Data.Typeable
+import GHC.StaticPtr
+
+main :: IO ()
+main = do
+ -- For some reason, removing the type signature below causes @g@ to appear
+ -- in the desugarer with a coercion like:
+ -- main@main:Main.g{v r20J} |> (Sub cobox_a36d{v}[lid])
+ print $ deRefStaticPtr (static g :: StaticPtr String)
+ -- For some reason, removing the type signature below causes an assertion
+ -- failure in the compiler:
+ --
+ -- ASSERT failed! file compiler/typecheck/TcType.lhs line 645
+ print $ deRefStaticPtr (static t_field :: StaticPtr (T Char -> Char)) $ T 'b'
+
+g :: String
+g = "found"
+
+data T a = T { t_field :: a }
+ deriving Typeable