Greetings :) I have the following simple program for which Hat does not seem to produce compilable code. I'm using hat 2.02 which I built from source. I'm using ghc 5.04.2 from a Debian package. I'm using hmake 3.07 from a Debian package. Any suggestions? peace, isaac --------------- Program module Main where main = putStr (show $ 4 ^ 2) --------------- GHC Error: % hmake -hat Approach hat-trans Approach.hs Wrote Hat/Approach.hs ghc -c -package hat -o Hat/Approach.o Hat/Approach.hs Hat/Approach.hs:13: Ambiguous type variable(s) `a' in the constraint `Num a' arising from use of `gfromInteger' at Hat/Approach.hs:13 In the third argument of `Hat.Hat.ap1', namely `(gfromInteger p3v23 p)' In the fifth argument of `Hat.Hat.uapp2', namely `(Hat.Hat.ap1 p3v23 p (gfromInteger p3v23 p) (Hat.Hat.conInteger p3v23 p 4))' Hat/Approach.hs:13: Ambiguous type variable(s) `a1' in the constraint `Integral a1' arising from use of `*^' at Hat/Approach.hs:13 In the fourth argument of `Hat.Hat.uapp2', namely `(*^)' In the sixth argument of `Hat.Hat.uapp2', namely `(Hat.Hat.uapp2 p3v25 p (+^) (*^) (Hat.Hat.ap1 p3v23 p (gfromInteger p3v23 p) (Hat.Hat.conInteger p3v23 p 4)) (Hat.Hat.ap1 p3v27 p (gfromInteger p3v27 p) (Hat.Hat.conInteger p3v27 p 2)))' --------------- Generated Code module Main where import qualified Prelude import qualified Hat.Hat as T import qualified Hat.PreludeBasic import Hat.Prelude gmain pmain p = T.constUse pmain p smain smain = T.constDef T.mkRoot amain (\ p -> T.uapp1 p3v8 p aputStr hputStr (T.uapp2 p3v21 p (+$) (*$) (gshow p3v16 p) (T.uapp2 p3v25 p (+^) (*^) (T.ap1 p3v23 p (Hat.PreludeBasic.gfromInteger p3v23 p) (T.conInteger p3v23 p 4)) (T.ap1 p3v27 p (Hat.PreludeBasic.gfromInteger p3v27 p) (T.conInteger p3v27 p 2))))) tMain = T.mkModule "Main" "Approach.hs" Prelude.True amain = T.mkVariable tMain 30001 3 0 "main" Prelude.False p3v1 = T.mkSrcPos tMain 30001 p3v8 = T.mkSrcPos tMain 30008 p3v21 = T.mkSrcPos tMain 30021 p3v16 = T.mkSrcPos tMain 30016 p3v25 = T.mkSrcPos tMain 30025 p3v23 = T.mkSrcPos tMain 30023 p3v27 = T.mkSrcPos tMain 30027 main = T.traceIO "Approach" (Main.gmain T.mkNoSrcPos T.mkRoot)
I have the following simple program for which Hat does not seem to produce compilable code.
main = putStr (show $ 4 ^ 2)
Any suggestions?
Yes. You came across a restriction of Hat which, as I just notice, is unfortunately not documented. This example needs type defaulting to work. You can see in Hugs Prelude> :t putStr (show $ 4 ^ 2) putStr (show $ 4 ^ 2) :: (Integral a, Num b) => IO () "a" and "b" are the types of "4" and "2", and the defaulting mechanism of Haskell sets them to "Integer". In the Hat-transformed code defaulting does not apply, because the transformed code uses different classes "Integeral", "Num" etc, but by definition defaulting only applies to a set number of standard numeric classes. The simple solution is to add type annotations: main = putStr (show $ (4::Integer) ^ (2::Integer)) Don't worry, in practice this situation occures very rarely. (Only twice in the Haskell standard libraries.) However, an "ambiguous type variable" error message is a clear indicator of this problem. To locate in your module where you have to place a type annotation, just add "default ()" to the module and compile it normally. Olaf -- OLAF CHITIL, Dept. of Computer Science, The University of York, York YO10 5DD, UK. URL: http://www.cs.york.ac.uk/~olaf/ Tel: +44 1904 434756; Fax: +44 1904 432767
participants (2)
-
Isaac Jones -
Olaf Chitil