# mapfoldr(f, op, itr)

``````..  mapfoldr(f, op, itr)

Like ``mapfoldr(f, op, v0, itr)``, but using the first element of
``itr`` as ``v0``. In general, this cannot be used with empty
collections (see ``reduce(op, itr)``).``````

## Examples

1. Apply a function and a binary operator to an iterable in a right-associative manner:

``````julia> add(x, y) = x + y;
julia> multiply(x, y) = x * y;
julia> mapfoldr(multiply, add, 1, [2, 3, 4])
25``````

This example applies the `multiply` function and the `add` binary operator to the elements of the iterable in a right-associative manner. The initial value `v0` is set to `1`, and the iterable is `[2, 3, 4]`.

2. Perform a right-associative reduction on a collection of strings:

``````julia> concat(s1, s2) = s1 * s2;
julia> mapfoldr(concat, string, "", ["Hello", " ", "World"])
"World Hello"``````

Here, the `concat` function is used to concatenate strings in a right-associative manner. The binary operator `string` is used to convert the elements of the iterable to strings, and the initial value `v0` is an empty string. The iterable is `["Hello", " ", "World"]`.

3. Handle an empty iterable:
``````julia> mapfoldr(iseven, ||, false, [])
false``````

This example demonstrates how the `mapfoldr` function handles an empty iterable. The initial value `v0` is set to `false`, and since there are no elements in the iterable, `v0` is returned as the result.

Common mistake example:

``````julia> mapfoldr(sqrt, +, 0, [1, 4, 9])
ERROR: MethodError: no method matching sqrt(::Int64)``````

In this example, the `sqrt` function is applied to the elements of the iterable, but it can only operate on floating-point numbers. It's important to ensure that the function passed to `mapfoldr` is compatible with the elements in the iterable to avoid such errors.