Hi All
I can successfully compile the following code using ghci
import Data.Array.IArray
makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <-
[lower..upper]
tridiagonal_solve (a, b, c, d, (lower, upper)) = x
where
gen_array f = (makeArray (lower, upper) f)
x = gen_array x_f
where
x_f i
| i == upper = (d_dash ! upper)
| otherwise = (d_dash ! i) - (c_dash !
i) * (x ! (i + 1))
d_dash = gen_array d_dash_f
where
d_dash_f i
| i == lower = (d ! lower) / (b ! lower)
| otherwise = ((d ! i) - (d_dash ! (i -
1)) * (a ! i)) /
((b ! i) - (c_dash ! (i -
1)) * (a ! i))
c_dash = gen_array c_dash_f
where
c_dash_f i
| i == lower = (c ! lower) / (b ! lower)
| otherwise = (c ! i) /
((b ! i) - (c_dash ! (i -
1)) * (a ! i))
I then attempted to write a type signature for tridiagonal_solve. I
didn't succeed at this however, all of my type signatures gave
compile errors when attempting to load them in ghci. I asked in the
#haskell channel, and they suggested that I try the type signature
from ghci :type function.
So I removed any type signatures, and reloaded the file in ghci, and
typed ":type tridiagonal_solve" which produced the following output:
tridiagonal_solve :: (IArray a3 e,
IArray a6 e,
IArray a7 e,
Fractional e,
Ix a,
Num a,
IArray a4 e,
IArray a2 e,
IArray a5 e,
IArray a1 e,
Enum a) =>
(a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7
a e
I then attempted to paste this into my code, the resulting code
looking like this:
import Data.Array.IArray
makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <-
[lower..upper]]
tridiagonal_solve :: (IArray a3 e,
IArray a6 e,
IArray a7 e,
Fractional e,
Ix a,
Num a,
IArray a4 e,
IArray a2 e,
IArray a5 e,
IArray a1 e,
Enum a) =>
(a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7
a e
tridiagonal_solve (a, b, c, d, (lower, upper)) = x
where
gen_array f = (makeArray (lower, upper) f)
x = gen_array x_f
where
x_f i
| i == upper = (d_dash ! upper)
| otherwise = (d_dash ! i) - (c_dash ! i)
* (x ! (i + 1))
d_dash = gen_array d_dash_f
where
d_dash_f i
| i == lower = (d ! lower) / (b ! lower)
| otherwise = ((d ! i) - (d_dash ! (i -
1)) * (a ! i)) /
((b ! i) - (c_dash ! (i -
1)) * (a ! i))
c_dash = gen_array c_dash_f
where
c_dash_f i
| i == lower = (c ! lower) / (b ! lower)
| otherwise = (c ! i) /
((b ! i) - (c_dash ! (i -
1)) * (a ! i))
When I attempt to load this into ghci, I recieve the following error:
[1 of 1] Compiling Main ( main.lhs, interpreted )
main.lhs:29:11:
Could not deduce (IArray a1 e)
from the context (IArray a3 e,
IArray a6 e,
IArray a7 e,
Fractional e,
Ix a2,
Num a2,
IArray a4 e,
IArray a21 e,
IArray a5 e,
IArray a11 e,
Enum a2)
arising from a use of `gen_array' at main.lhs:29:11-28
Possible fix:
add (IArray a1 e) to the context of
the type signature for `tridiagonal_solve'
In the expression: gen_array d_dash_f
In the definition of `d_dash':
d_dash = gen_array d_dash_f
where
d_dash_f i | i == lower = (d ! lower) / (b ! lower)
| otherwise
= ((d ! i) - (d_dash ! (i - 1)) * (a !
i))
/ ((b ! i) - (c_dash ! (i - 1)) * (a !
i))
In the definition of `tridiagonal_solve':
tridiagonal_solve (a, b, c, d, (lower, upper))
= x
where
gen_array f = (makeArray (lower,
upper) f)
x = gen_array x_f
where
x_f i | i == upper = (d_dash !
upper)
| otherwise
= (d_dash ! i) -
(c_dash ! i) * (x ! (i + 1))
d_dash = gen_array d_dash_f
where
d_dash_f i | i == lower =
(d ! lower) / (b ! lower)
| otherwise
= ((d ! i) -
(d_dash ! (i - 1)) * (a ! i))
/ ((b ! i) -
(c_dash ! (i - 1)) * (a ! i))
c_dash = gen_array c_dash_f
where
c_dash_f i | i == lower =
(c ! lower) / (b ! lower)
| otherwise
= (c ! i)
/ ((b ! i) -
(c_dash ! (i - 1)) * (a ! i))
main.lhs:35:11:
Could not deduce (IArray a e)
from the context (IArray a3 e,
IArray a6 e,
IArray a7 e,
Fractional e,
Ix a2,
Num a2,
IArray a4 e,
IArray a21 e,
IArray a5 e,
IArray a11 e,
Enum a2)
arising from a use of `gen_array' at main.lhs:35:11-28
Possible fix:
add (IArray a e) to the context of
the type signature for `tridiagonal_solve'
In the expression: gen_array c_dash_f
In the definition of `c_dash':
c_dash = gen_array c_dash_f
where
c_dash_f i | i == lower = (c ! lower) / (b ! lower)
| otherwise = (c ! i) / ((b ! i) -
(c_dash ! (i - 1)) * (a ! i))
In the definition of `tridiagonal_solve':
tridiagonal_solve (a, b, c, d, (lower, upper))
= x
where
gen_array f = (makeArray (lower,
upper) f)
x = gen_array x_f
where
x_f i | i == upper = (d_dash !
upper)
| otherwise
= (d_dash ! i) -
(c_dash ! i) * (x ! (i + 1))
d_dash = gen_array d_dash_f
where
d_dash_f i | i == lower =
(d ! lower) / (b ! lower)
| otherwise
= ((d ! i) -
(d_dash ! (i - 1)) * (a ! i))
/ ((b ! i) -
(c_dash ! (i - 1)) * (a ! i))
c_dash = gen_array c_dash_f
where
c_dash_f i | i == lower =
(c ! lower) / (b ! lower)
| otherwise
= (c ! i)
/ ((b ! i) -
(c_dash ! (i - 1)) * (a ! i))
My question is, what should the type signature for tridiagonal_solve
actually be? I would like one that doesn't limit the generality of
tridiagonal_solve because I would like to pass different array types
in the one function invocation, as long as they have the same index
and element types. I'm happy if other functions need type signatures
as well.
I'm using ghc 6.8.2 on windows, though I get a similar issue with
ghc 6.4.1.
Thanks.
Clinton
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