Question

Question in Haskell language?

Suppose that oho is the list ['o', 'h', 'n', 'o'] and that yikes is the list "yikes". For each of the following, say whether it is legal or illegal in Haskell. And wy is it illegal?

1. ohno:'y'

2. ohno ++ yikes

3. ohno:yikes

4. ['o']:yikes

5. 'o':yikes

Answer 1

1. ohno:'y'

: is the “prepend” operator. So [] is list and x:[] is prepending x to list.

this statement is illegal as the variable on left side of (:) is a list rather than an element.

2. ohno ++ yikes

this is concatenation of list. As both are list this statement is lega.

3. ohno:yikes

This is illegal. Reason is same as 1. We are prepending list to a list but (:) operator prepend only single element.

4. ['o']:yikes

this is illegal. ['o'] is a list of single character.

5. 'o':yikes

this is legal statement. as we are prepending 'o' a single char appending to list of char. yikes is list of char