Problem Statement

Create a list of ten functions, in the simplest manner possible   (anonymous functions are encouraged),   such that the function at index   i   (you may choose to start   i   from either   0   or   1),   when run, should return the square of the index,   that is,   i 2. Display the result of running any but the last function, to demonstrate that the function indeed remembers its value.

Demonstrate how to create a series of independent closures based on the same template but maintain separate copies of the variable closed over. In imperative languages, one would generally use a loop with a mutable counter variable. For each function to maintain the correct number, it has to capture the value of the variable at the time it was created, rather than just a reference to the variable, which would have a different value by the time the function was run. See also: Multiple distinct objects

Let's start with the solution:

USING: io kernel locals math prettyprint sequences ;

[let
    ! Create a sequence of 10 quotations
    10 iota [
        :> i            ! Bind lexical variable i
        [ i i * ]       ! Push a quotation to calculate i squared
    ] map :> seq

    { 3 8 } [
        dup pprint " squared is " write
        seq nth call .
    ] each
]


USING: fry io kernel math prettyprint sequences ;

! Push a sequence of 10 quotations
10 iota [
    '[ _ dup * ]        ! Push a quotation ( i -- i*i )
] map

{ 3 8 } [
    dup pprint " squared is " write
    over nth call .
] each
drop