I already discoursed on this at some length.
(1) In my own answer, I used code to map direction names to vectors.
But the Dictionary answers are absolutely fine.
(2) I pointed out that there are ALREADY "turn left" and "turn right"
operations on Points.
(3) An elegant solution is one which wastes no effort.
Introducing classes that you don't need is definitely wasted
effort.
WARNING: untested first draft code (can't find the tested stuff).
obey: commands
|position direction|
position := 0@0.
direction := 1@0.
commands do: [:each |
each caseOf: {
[$A] -> [position := position + direction].
[$L] -> [direction := direction leftRotated].
[$R] -> [direction := direction rightRotated]
}].
^{position. direction}
You will need to fiddle with this a bit to get the mapping between
problem coordinates and solution coordinates right, and you'll
need that Dictionary mapping directions to direction names, but
that's pretty much it. If you define more than one class for this
problem, your code is not elegant.
On Fri, 19 Apr 2019 at 08:05, Tim Mackinnon <tim@testit.works> wrote:
> You quickly find it’s a more interesting exercise than just a “point and
> dictionary”, particularly if you want to do it in an elegant Smalltalk way
> (but not over do it either).
>
> The interesting bit is that when facing a new direction, you need to know
> how to advance in that direction , and also what “left” and “right” of that
> direction are too. So it teases out having some objects and techniques for
> this.
>
> For those interested - join exercism-Pharo (
> https://exercism.io/tracks/pharo-smalltalk/installation) in non mentor
> mode and you can easily download it with the tests and try it out yourself
> (without running through the other exercises).
>
> Tim
>
> Sent from my iPhone
>
> On 18 Apr 2019, at 21:41, Richard Sargent <
> richard.sarg...@gemtalksystems.com> wrote:
>
> Your system would have instance variables holding the cardinal directions
> and another holding the current direction vector.
> e.g.
> north := DirectionVector x: 0 y: 1 name: 'north'.
>
> Your robot would implement e.g. #faceNorth to assign the "north" direction
> vector to the current direction vector instance variable.
>
>
>
> On Thu, Apr 18, 2019 at 12:17 PM Roelof Wobben <r.wob...@home.nl> wrote:
>
>> oke, and how must I see those classes and elemating the need for a lookup.
>>
>> it may be explained in pseudo-code.
>>
>> Roelof
>>
>>
>>
>> Op 18-4-2019 om 20:28 schreef Richard Sargent:
>>
>> On Thu, Apr 18, 2019 at 10:33 AM Roelof Wobben <r.wob...@home.nl> wrote:
>>
>>> oke
>>>
>>> Maybe I understand something not right,
>>>
>>> Lets say we have this scenario.
>>>
>>> Robot is on position (0,0)
>>> now it turns left so the robot faces East
>>>
>>
>> I don't understand what position has to do with direction nor why that
>> would be a problem. They are two distinct attributes.
>> Point and Dictionary are sufficient classes to model the limited
>> requirements of this exercise.
>> You could model a new class DirectionVector which internalizes the Point
>> used to provide the direction and provides its own name, eliminating the
>> need for a look up of any kind.
>>
>>
>>> or this scenario
>>>
>>> Robot is on position (0,0)
>>> now it turns right so the robot faces west.
>>>
>>> it looks that dictionary cannot provide this answer.
>>> or do I overlook something
>>>
>>> Roelof
>>>
>>>
>>>
>>> Op 18-4-2019 om 19:17 schreef Richard Sargent:
>>>
>>> On Thu, Apr 18, 2019 at 10:01 AM Roelof Wobben <r.wob...@home.nl> wrote:
>>>
>>>> yep, I have read that one
>>>> but I never gets a answer how I can "convert" a point to something
>>>> like north, east
>>>>
>>>> because the challenge wants this to be the answer :
>>>>
>>>> (Dictionary new
>>>> add: 'direction' -> 'north';
>>>> add:
>>>> 'position'
>>>> ->
>>>> (Dictionary new
>>>> add: 'x' -> 0;
>>>> add: 'y' -> 0;
>>>> yourself);
>>>> yourself)
>>>>
>>>
>>> If you have previously defined a "representation map", you would be
>>> golden.
>>>
>>> e.g.
>>> Dictionary new
>>> at: self northDirectionVector put: 'north';
>>> at: self eastDirectionVector put: 'east';
>>> at: self southDirectionVector put: 'south';
>>> at: self westDirectionVector put: 'west';
>>> yourself.
>>>
>>> Then:
>>> (Dictionary new
>>> add: 'direction' -> (self directionRepresentationMap at:
>>> self directionVector);
>>> ...
>>>
>>>
>>>>
>>>> and I think I need then to use if then , which I try to avoid as much
>>>> as possible.
>>>>
>>>> Roelof
>>>>
>>>>
>>>>
>>>> Op 18-4-2019 om 18:33 schreef Richard Sargent:
>>>>
>>>> On Thu, Apr 18, 2019 at 8:57 AM Roelof Wobben <r.wob...@home.nl> wrote:
>>>>
>>>>> Hello,
>>>>>
>>>>> I know I have asked earlier but im still stuck on this one :
>>>>> https://github.com/exercism/problem-specifications/blob/master/exercises/robot-simulator/description.md
>>>>>
>>>>> I tried with all double dispatch but that will be a lot of duplicate
>>>>> classes
>>>>>
>>>>> The problem I cannot solve right is that a robot can move or turn.
>>>>> when a robot turns only the direction the robot is facing changes and the
>>>>> position not. when a robot moves the facing direction stays the same but
>>>>> the position changes. but the change is dependend on the facing. Also the
>>>>> new facing direction is dependend on the old facing direction/
>>>>> How can I model this the best.
>>>>>
>>>>> I already have a object Robot that contains the facing direction and
>>>>> the current position
>>>>> or tried without it but then I use a lot of if then's
>>>>>
>>>>>
>>>>> so it there a better way to model this problem so it will be all
>>>>> nice and readable code.
>>>>>
>>>>
>>>> If I remember correctly, Richard O'Keefe gave you a viable design. 1)
>>>> Use a Point for your direction vector. 2) Use a second Point for your
>>>> position.
>>>>
>>>> e.g. if you align the compass with a Cartesian plane, 0@1 is North, 0@-1
>>>> is South, 1@0 is East, and -1@0 is West. When you move, you add the
>>>> direction vector to your current position. If you allow movements of
>>>> greater than a single unit, you multiply the direction vector by the
>>>> distance before adding that product to the position.
>>>>
>>>>
>>>>> Roelof
>>>>>
>>>>>
>>>>
>>>
>>
