Question

Without looking at the definitions from the standard prelude, define the following library functions on lists using recursion. a. Decide if all logical values in a list are True: $$ \text { and :: [Bool] } \rightarrow \text { Bool } $$ b. Concatenate a list of lists: $$ \text { concat :: [[a]] } \rightarrow[a] $$ c. Produce a list with $n$ identical elements: $$ \text { replicate :: Int } \rightarrow \text { a } \rightarrow \text { [a] } $$ d. Select the nth element of a list: $$ \text { (!!) :: [a] } \rightarrow \text { Int } \rightarrow a $$ e. Decide if a value is an element of a list: $$ \text { elem :: Eq a } \Rightarrow a \rightarrow[a] \rightarrow \text { Bool } $$ Note: most of these functions are defined in the prelude using other library functions rather than using explicit recursion, and are generic functions rather than being specific to the type of lists.

   Without looking at the definitions from the standard prelude, define the following library functions on lists using recursion.
a. Decide if all logical values in a list are True:
$$
\text { and :: [Bool] } \rightarrow \text { Bool }
$$
b. Concatenate a list of lists:
$$
\text { concat :: [[a]] } \rightarrow[a]
$$
c. Produce a list with $n$ identical elements:
$$
\text { replicate :: Int } \rightarrow \text { a } \rightarrow \text { [a] }
$$
d. Select the nth element of a list:
$$
\text { (!!) :: [a] } \rightarrow \text { Int } \rightarrow a
$$
e. Decide if a value is an element of a list:
$$
\text { elem :: Eq a } \Rightarrow a \rightarrow[a] \rightarrow \text { Bool }
$$
Note: most of these functions are defined in the prelude using other library functions rather than using explicit recursion, and are generic functions rather than being specific to the type of lists.
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Programming in Haskell
Programming in Haskell
Graham Hutton 2nd Edition
Chapter 6, Problem 6 ↓

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To decide if all logical values in a list are True, we can use recursion to check each element of the list. If we encounter a False, we can immediately return False, as that means not all values are True. If we reach the end of the list without encountering a  Show more…

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Without looking at the definitions from the standard prelude, define the following library functions on lists using recursion. a. Decide if all logical values in a list are True: $$ \text { and :: [Bool] } \rightarrow \text { Bool } $$ b. Concatenate a list of lists: $$ \text { concat :: [[a]] } \rightarrow[a] $$ c. Produce a list with $n$ identical elements: $$ \text { replicate :: Int } \rightarrow \text { a } \rightarrow \text { [a] } $$ d. Select the nth element of a list: $$ \text { (!!) :: [a] } \rightarrow \text { Int } \rightarrow a $$ e. Decide if a value is an element of a list: $$ \text { elem :: Eq a } \Rightarrow a \rightarrow[a] \rightarrow \text { Bool } $$ Note: most of these functions are defined in the prelude using other library functions rather than using explicit recursion, and are generic functions rather than being specific to the type of lists.
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