Long-time programmer/newbie with Haskell...

Thought I'd check out a program I saw at https://programmingpraxis.com/2019/12/13/pentabonacci-numbers/#comments:

pdiv (a:s) t = a : pdiv (zipWith (-) (s ++ repeat 0) (map (*a) t)) t
take 20 (pdiv [1] [-1,-1])
take 20 (pdiv [0,1] [-1,-1,-1,-1,-1])

I entered at the Haskell Online Compiler (https://paiza.io/projects/HEXouZ1jmJjemSO1cULHoA?language=haskell) and on my iOS Haskell app and got the same error:

[1 of 1] Compiling Main ( Main.hs, Main.o )

Main.hs:3:1: error:
Parse error: naked expression at top level
Perhaps you intended to use TemplateHaskell

Interestingly on my Windows 10 GHCi app, it worked fine:

GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help
Prelude> pdiv (a:s) t = a : pdiv (zipWith (-) (s ++ repeat 0) (map (*a) t)) t Prelude> take 20 (pdiv [1] [-1,-1]) [1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765]
Prelude> take 20 (pdiv [0,1] [-1,-1,-1,-1,-1]) [0,1,1,2,4,8,16,31,61,120,236,464,912,1793,3525,6930,13624,26784,52656,103519] Prelude>

I'm sure it's some formatting issue. I would appreciate any assistance you folks could offer.

Thanks, Steve

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On Friday, December 13, 2019 at 6:07:18 PM UTC-8, Ben Bacarisse wrote:

Steve Graham <xxxx> writes:

Long-time programmer/newbie with Haskell...

Thought I'd check out a program I saw at https://programmingpraxis.com/2019/12/13/pentabonacci-numbers/#comments:

pdiv (a:s) t = a : pdiv (zipWith (-) (s ++ repeat 0) (map (*a) t)) t
take 20 (pdiv [1] [-1,-1])
take 20 (pdiv [0,1] [-1,-1,-1,-1,-1])

I entered at the Haskell Online Compiler (https://paiza.io/projects/HEXouZ1jmJjemSO1cULHoA?language=haskell)
and on my iOS Haskell app and got the same error:

[1 of 1] Compiling Main ( Main.hs, Main.o )

Main.hs:3:1: error:
Parse error: naked expression at top level
Perhaps you intended to use TemplateHaskell

Interestingly on my Windows 10 GHCi app, it worked fine:

GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help
Prelude> pdiv (a:s) t = a : pdiv (zipWith (-) (s ++ repeat 0) (map (*a) t)) t
Prelude> take 20 (pdiv [1] [-1,-1]) [1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765] Prelude> take 20 (pdiv [0,1] [-1,-1,-1,-1,-1]) [0,1,1,2,4,8,16,31,61,120,236,464,912,1793,3525,6930,13624,26784,52656,103519]
Prelude>

I'm sure it's some formatting issue. I would appreciate any
assistance you folks could offer.

It's not a formatting issue. The interpreter will take expressions and evaluate them, but a Haskell program, suitable for compilation, can't
have "top-level" expressions.

The compilable, "program" version of what you wrote is

pdiv (a:s) t = a : pdiv (zipWith (-) (s ++ repeat 0) (map (*a) t)) t

main = do
print $ take 20 (pdiv [1] [-1,-1])
print $ take 20 (pdiv [0,1] [-1,-1,-1,-1,-1])

You would see the same error if you used ghc (rather than ghci) on your Windows box:

$ ghc p.hs
[1 of 1] Compiling Main ( p.hs, p.o )

p.hs:2:1: error:
Parse error: module header, import declaration
or top-level declaration expected.
|
2 | take 20 (pdiv [1] [-1,-1])
| ^^^^^^^^^^^^^^^^^^^^^^^^^^

--
Ben.

Thanks, Ben. The default for a new iOS Haskell program is:

main = do
putStr ""

Guess I should have realized that main = do was meant to be part of programs, at least some of them.

Steve

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Steve Graham <solitary.wanderer52@gmail.com> writes:

Long-time programmer/newbie with Haskell...

Thought I'd check out a program I saw at https://programmingpraxis.com/2019/12/13/pentabonacci-numbers/#comments:

pdiv (a:s) t = a : pdiv (zipWith (-) (s ++ repeat 0) (map (*a) t)) t
take 20 (pdiv [1] [-1,-1])
take 20 (pdiv [0,1] [-1,-1,-1,-1,-1])

I entered at the Haskell Online Compiler (https://paiza.io/projects/HEXouZ1jmJjemSO1cULHoA?language=haskell)
and on my iOS Haskell app and got the same error:

[1 of 1] Compiling Main ( Main.hs, Main.o )

Main.hs:3:1: error:
Parse error: naked expression at top level
Perhaps you intended to use TemplateHaskell

Interestingly on my Windows 10 GHCi app, it worked fine:

GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help
Prelude> pdiv (a:s) t = a : pdiv (zipWith (-) (s ++ repeat 0) (map (*a) t)) t Prelude> take 20 (pdiv [1] [-1,-1]) [1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765]
Prelude> take 20 (pdiv [0,1] [-1,-1,-1,-1,-1]) [0,1,1,2,4,8,16,31,61,120,236,464,912,1793,3525,6930,13624,26784,52656,103519]
Prelude>

I'm sure it's some formatting issue. I would appreciate any
assistance you folks could offer.

It's not a formatting issue. The interpreter will take expressions and evaluate them, but a Haskell program, suitable for compilation, can't
have "top-level" expressions.

The compilable, "program" version of what you wrote is

pdiv (a:s) t = a : pdiv (zipWith (-) (s ++ repeat 0) (map (*a) t)) t

main = do
print $ take 20 (pdiv [1] [-1,-1])
print $ take 20 (pdiv [0,1] [-1,-1,-1,-1,-1])

You would see the same error if you used ghc (rather than ghci) on your
Windows box:

$ ghc p.hs
[1 of 1] Compiling Main ( p.hs, p.o )

p.hs:2:1: error:
Parse error: module header, import declaration
or top-level declaration expected.
|
2 | take 20 (pdiv [1] [-1,-1])
| ^^^^^^^^^^^^^^^^^^^^^^^^^^

--
Ben.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)