Here’s a fun programming puzzle.

In any language, define a function `map`

that takes
another function `f`

and maps it over a list `l`

.
This means that `map`

returns a new list where `f`

has been applied to every element of `l`

.

An example in Python:

```
def map(f, l):
return [f(x) for x in l]
```

Here’s the catch: you can’t use any of your language’s iteration
constructs, e.g. `for`

, `while`

,
`each`

, or obviously any built-in `map`

. The above
example is banned because of the `for`

.

Sample solution:

We just use recursion instead of iteration

```
def map(f, l):
if len(l) == 0:
return []
return [f(l[0])] + map(f, l[1:])
```