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🎉 chapter1 #572

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🎉 chapter1 #572

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1c0aceb
🎉 chapter1
CypressVillage Jan 25, 2024
286780e
🐛 fix parse error
CypressVillage Jan 25, 2024
c57a80e
🐛 fix negative
CypressVillage Jan 25, 2024
0846d37
🐛 fix another negative
CypressVillage Jan 25, 2024
7a65dcb
🎉 chapter2
CypressVillage Jan 25, 2024
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72 changes: 43 additions & 29 deletions src/Chapter1.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -209,31 +209,31 @@
> Try to guess first and then compare your expectations with GHCi output

>>> :t True
<INSERT THE RESULT INSTEAD OF THE TEXT>
True :: Bool
>>> :t 'a'
<INSERT THE RESULT INSTEAD OF THE TEXT>
'a' :: Char
>>> :t 42
<INSERT THE RESULT INSTEAD OF THE TEXT>
42 :: Num a => a

A pair of boolean and char:
>>> :t (True, 'x')
<INSERT THE RESULT INSTEAD OF THE TEXT>
(True, 'x') :: (Bool, Char)

Boolean negation:
>>> :t not
<INSERT THE RESULT INSTEAD OF THE TEXT>
not :: Bool -> Bool

Boolean 'and' operator:
>>> :t (&&)
<INSERT THE RESULT INSTEAD OF THE TEXT>
(&&) :: Bool -> Bool -> Bool

Addition of two numbers:
>>> :t (+)
<INSERT THE RESULT INSTEAD OF THE TEXT>
(+) :: Num a => a -> a -> a

Maximum of two values:
>>> :t max
<INSERT THE RESULT INSTEAD OF THE TEXT>
max :: Ord a => a -> a -> a

You might not understand each type at this moment, but don't worry! You've only
started your Haskell journey. Types will become your friends soon.
Expand Down Expand Up @@ -301,43 +301,43 @@
functions and operators first. Remember this from the previous task? ;)

>>> 1 + 2
<INSERT THE RESULT INSTEAD OF THE TEXT>
3

>>> 10 - 15
<INSERT THE RESULT INSTEAD OF THE TEXT>
-5

>>> 10 - (-5) -- negative constants require ()
<INSERT THE RESULT INSTEAD OF THE TEXT>
15

>>> (3 + 5) < 10
<INSERT THE RESULT INSTEAD OF THE TEXT>
True

>>> True && False
<INSERT THE RESULT INSTEAD OF THE TEXT>
False

>>> 10 < 20 || 20 < 5
<INSERT THE RESULT INSTEAD OF THE TEXT>
True

>>> 2 ^ 10 -- power
<INSERT THE RESULT INSTEAD OF THE TEXT>
1024

>>> not False
<INSERT THE RESULT INSTEAD OF THE TEXT>
True

>>> div 20 3 -- integral division
<INSERT THE RESULT INSTEAD OF THE TEXT>
6

>>> mod 20 3 -- integral division remainder
<INSERT THE RESULT INSTEAD OF THE TEXT>
2

>>> max 4 10
<INSERT THE RESULT INSTEAD OF THE TEXT>
10

>>> min 5 (max 1 2)
<INSERT THE RESULT INSTEAD OF THE TEXT>
2

>>> max (min 1 10) (min 5 7)
<INSERT THE RESULT INSTEAD OF THE TEXT>
5

Because Haskell is a __statically-typed__ language, you see an error each time
you try to mix values of different types in situations where you are not
Expand Down Expand Up @@ -429,6 +429,7 @@
49
-}

squareSum :: Int -> Int -> Int
squareSum x y = (x + y) * (x + y)


Expand All @@ -449,7 +450,7 @@
function body with the proper implementation.
-}
next :: Int -> Int
next x = error "next: not implemented!"
next x = x + 1

{- |
After you've implemented the function (or even during the implementation), you
Expand Down Expand Up @@ -490,7 +491,8 @@
whether it works for you!
-}
-- DON'T FORGET TO SPECIFY THE TYPE IN HERE
lastDigit n = error "lastDigit: Not implemented!"
lastDigit :: Int -> Int
lastDigit = (`mod` 10) . abs
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That's pretty!

Nice work on using infix form of calling functions! We don't explain this syntax in our course to make it short. But well done 👍



{- |
Expand Down Expand Up @@ -520,7 +522,7 @@
satisfying the check will be returned and, therefore, evaluated.
-}
closestToZero :: Int -> Int -> Int
closestToZero x y = error "closestToZero: not implemented!"
closestToZero x y = if abs x < abs y then x else y


{- |
Expand Down Expand Up @@ -554,7 +556,11 @@
Casual reminder about adding top-level type signatures for all functions :)
-}

mid x y z = error "mid: not implemented!"
mid :: Int -> Int -> Int -> Int
mid x y z
| x <= y && y <= z = y
| x >= y && y >= z = y
| otherwise = mid y z x

{- |
=⚔️= Task 8
Expand All @@ -568,7 +574,8 @@
>>> isVowel 'x'
False
-}
isVowel c = error "isVowel: not implemented!"
isVowel :: Char -> Bool
isVowel = (`elem` "aoeiuv")
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Nice one! 👍🏼

One note in here, that sometimes, elem could be slower than the explicit pattern matching. I remember there were some benchmarks on one particular case, that showed how moving to pattern matching on each case separately drastically decrease time 🐎 But for this solution it is totally fine!



{- |
Expand Down Expand Up @@ -632,7 +639,12 @@
specifying complex expressions.
-}

sumLast2 n = error "sumLast2: Not implemented!"
sumLast2 :: Int -> Int
sumLast2 x =
let ax = abs x
last = ax `mod` 10

Check warning on line 645 in src/Chapter1.hs

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GitHub Actions / Chapter One (3.8, 9.4.4) 

This binding for ‘last’ shadows the existing binding

Check warning on line 645 in src/Chapter1.hs

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GitHub Actions / Build Learn4Haskell (3.8, 9.4.4) 

This binding for ‘last’ shadows the existing binding
secondlast = ax `mod` 100 `div` 10
Comment on lines +645 to +646
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That is a wonderful solution! 👏🏼 You correctly noticed that it is the div and mod, cool 😎

Another approach could be also using this: you can see that you use both:

mod m 10
div m 10

The standard library has the divMod function, that actually combines inside both div and mod. And this is exactly what you use!.

So you could write it this way:

(x, y) = divMod m 10

You can see how we could pattern match on the pair 🙂

in last + secondlast


{- |
Expand All @@ -653,8 +665,10 @@
aren't ready for this boss yet!
-}

firstDigit n = error "firstDigit: Not implemented!"

firstDigit :: Int -> Int
firstDigit x
| x `div` 10 == 0 = x
| otherwise = firstDigit (x `div` 10)
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I see, that for a negative numbers it will be not return the correct answer. Sometimes it is tricky to keep in mind all the edge cases, so no worries, but the idea and recursive solution is awesome 👏🏼


{-
You did it! Now it is time to open a pull request with your changes
Expand Down
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