haskell-book-exercises/ch12/ch12.adoc at 53d2d3aa64e981b63e2ba3c8d6c4234c23e4671a · argumatronic/haskell-book-exercises · GitHub

12 Signaling adversity

12.5 Chapter Exercises

Determine the kinds

id :: a → a kind of a is *
r :: a → f a kind of a is *, kind of f a is * -> *

String processing

Replace "the" with "a".
```
link:ch12_12.5_0.hs[role=include]
```
recursive count
```
link:ch12_12.5_1.hs[role=include]
```
number of vowels in a word - changed the siganture to Int instead of Integer
```
link:ch12_12.5_2.hs[role=include]
```

Validate the word

link:ch12_12.5_3.hs[role=include]

It’s only Natural

link:ch12_12.5_4.hs[role=include]

Small library for Maybe

boolean check
```
link:ch12_12.5_5.hs[role=include]
```
Maybe catamorphism
```
link:ch12_12.5_6.hs[role=include]
```
fallback
```
link:ch12_12.5_7.hs[role=include]
```
Converting between List and Maybe
```
link:ch12_12.5_8.hs[role=include]
```
drop the Nothing values from our list
```
link:ch12_12.5_9.hs[role=include]
```
flipMaybe
```
link:ch12_12.5_10.hs[role=include]
```

Small library for Either

use foldr
```
link:ch12_12.5_11.hs[role=include]
```
use foldr well, same as last one (don’t see the point much, just use a instead of b)
```
link:ch12_12.5_12.hs[role=include]
```
partitionEithers
```
link:ch12_12.5_13.hs[role=include]
```
eitherMaybe
```
link:ch12_12.5_14.hs[role=include]
```
either'
```
link:ch12_12.5_15.hs[role=include]
```
use either'

Warning
I don’t see the point :(
```
link:ch12_12.5_16.hs[role=include]
```

Write your own iterate and unfoldr

myIterate using recursion
```
link:ch12_12.5_17.hs[role=include]
```
myUnfoldr
```
link:ch12_12.5_18.hs[role=include]
```
myIterate into betterIterate using myUnfoldr
```
link:ch12_12.5_19.hs[role=include]
```

Finally something other than a list!

link:ch12_12.5_20.hs[role=include]