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4d47's solution

to Accumulate in the Perl 6 Track

Instructions
Test suite
Solution

Implement the accumulate operation, which, given a collection and an operation to perform on each element of the collection, returns a new collection containing the result of applying that operation to each element of the input collection.

Given the collection of numbers:

  • 1, 2, 3, 4, 5

And the operation:

  • square a number (x => x * x)

Your code should be able to produce the collection of squares:

  • 1, 4, 9, 16, 25

Check out the test suite to see the expected function signature.

Restrictions

Keep your hands off that collect/map/fmap/whatchamacallit functionality provided by your standard library! Solve this one yourself using other basic tools instead.

Resources

Remember to check out the Perl 6 documentation and resources pages for information, tips, and examples if you get stuck.

Running the tests

There is a test suite and module included with the exercise. The test suite (a file with the extension .t) will attempt to run routines from the module (a file with the extension .pm6). Add/modify routines in the module so that the tests will pass! You can view the test data by executing the command perl6 --doc *.t (* being the name of the test suite), and run the test suite for the exercise by executing the command prove . --exec=perl6 in the exercise directory. You can also add the -v flag e.g. prove . --exec=perl6 -v to display all tests, including any optional tests marked as 'TODO'.

Source

Conversation with James Edward Gray II https://twitter.com/jeg2

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

accumulate.t

#!/usr/bin/env perl6
use v6;
use Test;
use lib $?FILE.IO.dirname;
use Accumulate;
plan 6;

my Version:D $version = v2;

if Accumulate.^ver !~~ $version {
  warn "\nExercise version mismatch. Further tests may fail!"
    ~ "\nAccumulate is {Accumulate.^ver.gist}. "
    ~ "Test is {$version.gist}.\n";
}

is-deeply accumulate([ ], sub {}),
          [ ],
          'test empty';
is-deeply accumulate([1, 2, 3, 4, 5], sub { @_[0] * @_[0] }),
          [1, 4, 9, 16, 25],
          'raise to 2';
is-deeply accumulate([10, 17, 23], sub { [ (@_[0] / 7).truncate, (@_[0] % 7).truncate ] }),
          [[1, 3], [2, 3], [3, 2] ],
          'divmod';
is-deeply accumulate(['hello', 'exercism'], sub { @_[0].uc }),
          ['HELLO', 'EXERCISM'],
          'capitalize';
is-deeply accumulate(['a', 'b', 'c' ], sub ($inp) { [ accumulate( [1, 2, 3], sub ($inp2) { $inp ~ $inp2 } )]}),
          [['a1', 'a2', 'a3'], ['b1', 'b2', 'b3'], ['c1', 'c2', 'c3']],
          'recursive';
is-deeply accumulate(['the', 'quick', 'brown', 'fox'], sub { @_[0].flip }),
          ['eht', 'kciuq', 'nworb', 'xof'],
          'reverse strings';
unit class Accumulate;

method accumulate(Array $elems, Sub $fn --> Array) {
    my @results;
    @results.push: $fn($_) for $elems.values;
    @results
}

What can you learn from this solution?

A huge amount can be learnt from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that I could read more about to develop my understanding?