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<p class="MsoNormal">---------- Forwarded message ----------<br>
From: "Nenad Končar" <<a href="mailto:nlpresearcher@gmail.com" target="_blank">nlpresearcher@gmail.com</a>><br>
To: Levent Erkok <<a href="mailto:erkokl@gmail.com" target="_blank">erkokl@gmail.com</a>><br>
Cc: Gregory Guthrie <<a href="mailto:guthrie@miu.edu" target="_blank">guthrie@miu.edu</a>>, "<a href="mailto:haskell-cafe@haskell.org" target="_blank">haskell-cafe@haskell.org</a>" <<a href="mailto:haskell-cafe@haskell.org" target="_blank">haskell-cafe@haskell.org</a>>,
Haskell Community <<a href="mailto:replies%2Bf6607596e3ee63f105e2b0327b86f062@discourse.haskell.org" target="_blank">replies+f6607596e3ee63f105e2b0327b86f062@discourse.haskell.org</a>><br>
Bcc: <br>
Date: Sat, 1 Apr 2023 00:00:09 +0200<br>
Subject: Re: [Haskell-cafe] GPT & Haskell<o:p></o:p></p>
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<p class="MsoNormal">On Fri, 31 Mar 2023 at 23:24, Levent Erkok <<a href="mailto:erkokl@gmail.com" target="_blank">erkokl@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">This code is buggy when lo + hi overflows your integer type. Classic (extremely) corner case bug: <a href="https://ai.googleblog.com/2006/06/extra-extra-read-all-about-it-nearly.html" target="_blank">https://ai.googleblog.com/2006/06/extra-extra-read-all-about-it-nearly.html</a>
<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">Thank you kindly for pointing this out. GPT-4, when prompted, is able to detect and correct the overflow mistake as follows:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">After I introduced a purposeful mistake in the Haskel code, I prompted GPT-4 as follows:<o:p></o:p></p>
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<p class="MsoNormal"><b>If the following Haskel code contains any logical mistakes then correct the code for me:<br>
<br>
<br>
-- Binary search in Haskell<br>
-- Precondition: the list is sorted in ascending order<br>
-- Postcondition: the function returns the index of the target element if found, or Nothing otherwise<br>
-- Invariant: the search space is always within the bounds of the list<br>
-- Variant: the search space decreases by half at each recursive call<br>
-- Internal state: the lower and upper bounds of the search space<br>
<br>
binarySearch :: Ord a => [a] -> a -> Maybe Int<br>
binarySearch xs x = go xs x 0 (length xs - 1)<br>
where<br>
go xs x lo hi<br>
| lo > hi = Nothing -- base case: search space is empty<br>
| x == midElem = Just mid -- base case: target element is found<br>
| x < midElem = go xs x lo (mid - 1) -- recursive case: search in the left half<br>
| otherwise = go xs x (mid + 1) hi -- recursive case: search in the right half<br>
where<br>
mid = (lo - hi) `div` 2 -- calculate the middle index<br>
midElem = xs !! mid -- get the middle element<br>
<br>
-- Print results using putStrLn<br>
main :: IO ()<br>
main = do<br>
let xs = [1, 3, 5, 7, 9] -- a sorted list of integers<br>
let x = 5 -- a target element to search for<br>
let result = binarySearch xs x -- call the binary search function<br>
case result of -- pattern match on the result<br>
Nothing -> putStrLn "Element not found" -- print a message if Nothing is returned<br>
Just i -> putStrLn $ "Element found at index " ++ show i -- print a message with the index if Just i is returned</b><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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and then GPT-4 replied:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:10.5pt;font-family:"Segoe UI",sans-serif;color:#717171;background:white">Hello,</span></b><b><span style="font-size:10.5pt;font-family:"Segoe UI",sans-serif;color:#717171"><br>
<br>
<span style="background:white">Thank you for sending me your Haskell code for binary search. I appreciate your interest in learning this functional programming language. I have reviewed your code and found a few logical mistakes that need to be corrected. Here
is the revised code with some comments explaining the changes:<br>
<br>
<br>
</span></span>-- Binary search in Haskell<br>
-- Precondition: the list is sorted in ascending order<br>
-- Postcondition: the function returns the index of the target element if found, or Nothing otherwise<br>
-- Invariant: the search space is always within the bounds of the list<br>
-- Variant: the search space decreases by half at each recursive call<br>
-- Internal state: the lower and upper bounds of the search space<br>
<br>
binarySearch :: Ord a => [a] -> a -> Maybe Int<br>
binarySearch xs x = go xs x 0 (length xs - 1)<br>
where<br>
go xs x lo hi<br>
| lo > hi = Nothing -- base case: search space is empty<br>
| x == midElem = Just mid -- base case: target element is found<br>
| x < midElem = go xs x lo (mid - 1) -- recursive case: search in the left half<br>
| otherwise = go xs x (mid + 1) hi -- recursive case: search in the right half<br>
where<br>
mid = lo + (hi - lo) `div` 2 -- calculate the middle index using a safer formula to avoid overflow<br>
midElem = xs !! mid -- get the middle element<br>
<br>
-- Print results using putStrLn<br>
main :: IO ()<br>
main = do<br>
let xs = [1, 3, 5, 7, 9] -- a sorted list of integers<br>
let x = 5 -- a target element to search for<br>
let result = binarySearch xs x -- call the binary search function<br>
case result of -- pattern match on the result<br>
Nothing -> putStrLn "Element not found" -- print a message if Nothing is returned<br>
Just i -> putStrLn $ "Element found at index " ++ show i -- print a message with the index if Just i is returned<br>
</b><b><span style="font-size:10.5pt;font-family:"Segoe UI",sans-serif;color:#717171"><br>
<br>
<span style="background:white">The main mistake in your code was in the calculation of the middle index. You used `(lo - hi) `div` 2`, which is incorrect because it will always give a negative value. The correct formula is `lo + (hi - lo) `div` 2`, which ensures
that the middle index is always within the bounds of the list. This formula also avoids overflow issues that might occur if you use `(lo + hi) `div` 2`.</span><br>
<br>
<span style="background:white">I hope this helps you understand binary search better and improve your Haskell skills. Please let me know if you have any questions or feedback. I would love to hear from you and help you further.</span><br>
<br>
<span style="background:white">Happy coding!</span></span> </b><br>
<br>
<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">The improved code runs:<o:p></o:p></p>
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<p class="MsoNormal"><b><a href="https://onecompiler.com/haskell/3z4avpx6n" target="_blank">https://onecompiler.com/haskell/3z4avpx6n</a></b><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Mar 31, 2023, at 1:02 PM, Gregory Guthrie <<a href="mailto:guthrie@miu.edu" target="_blank">guthrie@miu.edu</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">From a colleague:<o:p></o:p></p>
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<p class="MsoNormal"> GPT Pretty smart(?!).<o:p></o:p></p>
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<p class="MsoNormal">But this is of course simple, and searchable.<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">Still…<o:p></o:p></p>
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<p class="MsoNormal">--------------------------------------------------------------------------------------------------<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">GPT-4 when prompted:<o:p></o:p></p>
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<p class="MsoNormal"><b>Write binary search in Haskel. Print results using putStrLn. Ensure bug-free code by specifying preconditions, postconditions, invariants, variants, internal states.</b><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">gives the following response:<o:p></o:p></p>
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<p class="MsoNormal"><b>-- Binary search in Haskell<br>
-- Precondition: the list is sorted in ascending order<br>
-- Postcondition: the function returns the index of the target element if found, or Nothing otherwise<br>
-- Invariant: the search space is always within the bounds of the list<br>
-- Variant: the search space decreases by half at each recursive call<br>
-- Internal state: the lower and upper bounds of the search space<br>
<br>
binarySearch :: Ord a => [a] -> a -> Maybe Int<br>
binarySearch xs x = go xs x 0 (length xs - 1)<br>
where<br>
go xs x lo hi<br>
| lo > hi = Nothing -- base case: search space is empty<br>
| x == midElem = Just mid -- base case: target element is found<br>
| x < midElem = go xs x lo (mid - 1) -- recursive case: search in the left half<br>
| otherwise = go xs x (mid + 1) hi -- recursive case: search in the right half<br>
where<br>
mid = (lo + hi) `div` 2 -- calculate the middle index<br>
midElem = xs !! mid -- get the middle element<br>
<br>
-- Print results using putStrLn<br>
main :: IO ()<br>
main = do<br>
let xs = [1, 3, 5, 7, 9] -- a sorted list of integers<br>
let x = 5 -- a target element to search for<br>
let result = binarySearch xs x -- call the binary search function<br>
case result of -- pattern match on the result<br>
Nothing -> putStrLn "Element not found" -- print a message if Nothing is returned<br>
Just i -> putStrLn $ "Element found at index " ++ show i -- print a message with the index if Just i is returned</b><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">The above code runs:<o:p></o:p></p>
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<p class="MsoNormal"><b><a href="https://onecompiler.com/cpp/3z48yt2pp" target="_blank"><span style="color:#0563C1">https://onecompiler.com/cpp/3z48yt2pp</span></a></b><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><image001.png><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"SFHello-Regular",serif">_______________________________________________<br>
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Only members subscribed via the mailman list are allowed to post.</span><o:p></o:p></p>
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