#625: Incorrect handling of types
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Reporter: hjgtuyl (at) chello (dot) nl | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 6.4.1
Severity: normal | Keywords:
Os: Windows | Architecture: Unknown
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The following program, taken from
http://shootout.alioth.debian.org/benchmark.php?test=pidigits&lang=ghc&id=0 compiles without a problem:
-------------------------------------------------
import System
floor_ev (q, r, s, t) x = (q*x + r) `div` (s*x + t)
comp (q,r,s,t) (q',r',s',t') = (q*q' + r*s', q*r' + r*t', s*q' + t*s',
s*r' + t*t')
next z = floor_ev z 3
safe z n = n == floor_ev z 4
prod z n = comp (10,-10 * n, 0, 1) z
cons z k = let den = 2*k+1 in comp z (fromIntegral k, fromIntegral
(2*den), 0, fromIntegral
den)
digit :: Int -> (Integer,Integer,Integer,Integer) -> Int -> Int -> Int ->
IO ()
digit k z 0 row col = putStrLn (take (10-col) "
"++"\t:"++show (row+col))
digit k z n row col =
if safe z y
then if col == 10
then do let row' = row + 10
putStr ("\t:"++show row'++"\n"++show y)
digit k (prod z y) (n-1) row' 1
else putStr (show y) >> digit k (prod z y) (n-1) row (col+1)
else digit (k+1) (cons z k) n row col
where y = next z
main =
do [n] <- getArgs
digit 1 (1,0,0,1) (read n) 0 0
-------------------------------------------------
When substituting "safe z y" in the function "digits" with it's
definition, we get:
-------------------------------------------------
import System
floor_ev (q, r, s, t) x = (q*x + r) `div` (s*x + t)
comp (q,r,s,t) (q',r',s',t') = (q*q' + r*s', q*r' + r*t', s*q' + t*s',
s*r' + t*t')
next z = floor_ev z 3
safe z n = n == floor_ev z 4
prod z n = comp (10,-10 * n, 0, 1) z
cons z k = let den = 2*k+1 in comp z (fromIntegral k, fromIntegral
(2*den), 0, fromIntegral
den)
digit :: Int -> (Integer,Integer,Integer,Integer) -> Int -> Int -> Int ->
IO ()
digit k z 0 row col = putStrLn (take (10-col) "
"++"\t:"++show (row+col))
digit k z n row col =
if n == floor_ev z 4 -- safe z y
then if col == 10
then do let row' = row + 10
putStr ("\t:"++show row'++"\n"++show y)
digit k (prod z y) (n-1) row' 1
else putStr (show y) >> digit k (prod z y) (n-1) row (col+1)
else digit (k+1) (cons z k) n row col
where y = next z
main =
do [n] <- getArgs
digit 1 (1,0,0,1) (read n) 0 0
-------------------------------------------------
The compilation then fails with the message:
Pidigits2.hs:13:19:
Couldn't match `Int' against `Integer'
Expected type: (Int, Int, Int, Int)
Inferred type: (Integer, Integer, Integer, Integer)
In the first argument of `floor_ev', namely `z'
In the second argument of `(==)', namely `floor_ev z 4'
I suppose this is a correct message, but then the first version should not
have been compiled
either.
--
Ticket URL: <
http://cvs.haskell.org/trac/ghc/ticket/625>
GHC <
http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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