## `fp::fixedpt` -- returns fixed point of a function

#### Introduction

`fp::fixedpt``(f)` returns the fixed point of the unary function `f`.

#### Call(s)

`fp::fixedpt(f)`

#### Parameters

`f` | - | unary function

#### Returns

A unary function.

#### Details

- `fp::fixedpt` returns the fixed point of the unary function `f`.
- `fp::fixedpt` is implemented as the Y combinator which is defined as follows:

      Y := f -> g(f)(g(f))

  where the function g is defined as

      g := f -> (h -> (x -> f(h(h))(x)))

#### Example 1

A function computing the Fibonacci numbers is created as a fixed point:

    >> fb2 := (f,n) -> if n <= 2 then 1 else f(n-1) + f(n-2) end:
       fib := fp::fixedpt(fp::curry(fb2)):
       fib(i) $ i=1..9

                           1, 1, 2, 3, 5, 8, 13, 21, 34

#### Changes

- no changes

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