Re: [Pharo-users] difference between double dispatch and the method explains here

[Richard O'Keefe]

On this laptop I have
 - Squeak
 - Pharo
 - GNU Smalltalk
 - VisualAge Smalltalk
 - VisualWorks Smalltalk
 - Smalltalk/X
plus some oddballs like susie, amber, and CSOM.
On another laptop I have
 - Strongtalk
 - Dolphin
And of course I have my own 'astc' Smalltalk-via-C compiler.
I have to say that Dolphin is easily the most *beautiful* Smalltalk
environment I've used.  (Yes, I'm the kind of person who has four
different C compilers on the same machine and uses them all.  You
don't want to know how many Javascript implementations...)

The important thing here is that there are at least two aspects to
"Smalltalk".  There is Smalltalk-the-approach-to-OO and there is
Smalltalk-the-many-related-but-different-IDEs.  When it comes to
productivity, the IDE is important.  Really important.  But when
it comes to thinking about programming and solving tasks like
exercism ones, it's the approach that matters.  And that approach
pays off in languages like Javascript and Ruby and Python as well.

I used to be a University lecturer.  Now I'm a (sub)contractor.
I used to see a LOT of student code that
 - had way too many classes
 - did not use existing well-known classes when it should
 - failed to encapsulate private state
 - put responsibilities in the wrong places
and that was Java code.  What prepared me to see such issues in Java?

Lots and lots of practice in Smalltalk.

And lots of reading Smalltalk, and figuring out what made it easy or
hard to read.

I do not know how much time you have on your hands,
but you might find it profitable to look at
http://rosettacode.org/wiki/Rosetta_Code
specifically
http://rosettacode.org/wiki/Category:Smalltalk

Look at the bottom of that page for a list of 258
problems solved in Smalltalk.


On Tue, 9 Apr 2019 at 03:20, Roelof Wobben  wrote:

> Thanks,
>
> for the discusson and lessons.
>
> I will think about it and also think if smalltalk is for me.
> I did the pharo Mooc and still have a lot of problems making the smalltalk
> way click in my head so I can solve little problems like this.
>
> Out of coriousy what dialect do you use?
>
>
> Op 8-4-2019 om 17:11 schreef Richard O'Keefe:
>
> You are expected to use my code fragments for *ideas*,
> not to incorporate them *literally* in your code.  As
> I explained, *without seeing the specification*, I have
> no way to tell whether the specification uses a left-handed
> or right-handed coordinate system.
>
> For what it's worth, here's a complete program in my
> Smalltalk dialect.  It doesn't plug into the exercism
> testing framework because I can do not know what it
> looks like.  But if it makes the code more complicated
> that this, it's doing it wrong.
>
> require: 'geometry.st'  "Point"
> require: 'print.st' "OutputStream>>print:"
>
> Object subclass: #Robot
>   instanceVariableNames: 'position direction'
>   poolDirectionaries:'FileStream'
>
>   methods for: 'initialising'
> pvtPostNew
>   position  := 0@0.
>   direction := 1@0.
>
>   methods for: 'accessing'
> direction
>   ^direction copy
>
> location
>   ^location copy
>
> obey: commands
>   commands do: [:each |
> each caseOf: {
>   [$A] -> [position  := position  + direction].
>   [$L] -> [direction := direction leftRotated].
>   [$R] -> [direction := direction rightRotated]
> }].
>
>   class methods for: 'main'
> start
>   [StdIn atEnd] whileFalse: [
>  |robot|
>  robot := Robot new.
>  Robot obey: StdIn nextLine.
>  StdOut print: Robot location; cr].
>
> On Tue, 9 Apr 2019 at 02:58, Roelof Wobben  wrote:
>
>> yes,  this is a real  tests from the pharo track on exercism.io
>>
>> I understand what you mean but maybe I overthinking things.
>> But if we have a robot facing north and the robot turns to the left  , im
>> my oponion it faces now to the east.
>>
>> like this test is saying :
>>
>>
>> test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth
>> | result |
>> result := robotSimulatorCalculator
>> moveDirection: 'east'
>> position:
>> (Dictionary new
>> add: 'x' -> 0;
>> add: 'y' -> 0;
>> yourself)
>> instructions: 'R'.
>> self
>> assert: result
>> equals:
>> (Dictionary new
>> add: 'direction' -> 'south';
>> add:
>> 'position'
>> ->
>> (Dictionary new
>> add: 'x' -> 0;
>> add: 'y' -> 0;
>> yourself);
>> yourself)
>>
>>
>> but I cannot come to the same outcome with this code :
>>
>>
>> pointToName: aPoint
>>   ^aPoint x isZero
>>  ifTrue:  [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]]
>>  ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
>>
>>
>> maybe 

Re: [Pharo-users] difference between double dispatch and the method explains here

[Roelof Wobben]

  
  
Thanks, 
  
  for the discusson and lessons. 
  
  I will think about it and also think if smalltalk is for me. 
  I did the pharo Mooc and still have a lot of problems making the
  smalltalk way click in my head so I can solve little problems like
  this.
  
  Out of coriousy what dialect do you use?
  
  
  Op 8-4-2019 om 17:11 schreef Richard O'Keefe:


  
  

  You are expected to
use my code fragments for *ideas*,
  not to incorporate
them *literally* in your code.  As
  I explained,
*without seeing the specification*, I have
  no way to tell
whether the specification uses a left-handed
  or right-handed
coordinate system.
  
  
  For what it's worth,
here's a complete program in my
  Smalltalk dialect. 
It doesn't plug into the exercism
  testing framework
because I can do not know what it
  looks like.  But if
it makes the code more complicated
  that this, it's
doing it wrong.
  
  
  require: 'geometry.st' 
"Point"
require: 'print.st'
"OutputStream>>print:"
    
Object subclass: #Robot
  instanceVariableNames: 'position direction'
  poolDirectionaries:    'FileStream'

  methods for: 'initialising'
    pvtPostNew
  position  := 0@0.
  direction := 1@0.

  methods for: 'accessing'
    direction
  ^direction copy

    location
  ^location copy

    obey: commands
  commands do: [:each |
    each caseOf: {
  [$A] -> [position  := position  + direction].
  [$L] -> [direction := direction leftRotated].
  [$R] -> [direction := direction rightRotated]
    }].

  class methods for: 'main'
    start
  [StdIn atEnd] whileFalse: [
 |robot|
 robot := Robot new.
 Robot obey: StdIn nextLine.
 StdOut print: Robot location; cr].
  

  
  
  
On Tue, 9 Apr 2019 at 02:58,
  Roelof Wobben  wrote:


  
yes, 
  this is a real  tests from the pharo track on exercism.io
  
  I understand what you mean but maybe I overthinking
  things. 
  But if we have a robot facing north and the robot turns to
  the left  , im my oponion it faces now to the east. 
  
  like this test is saying : 
  
test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth
      | result |
      result := robotSimulatorCalculator
          moveDirection: 'east'
          position:
              (Dictionary new
                  add: 'x' -> 0;
                  add: 'y' -> 0;
                  yourself)
          instructions: 'R'.
      self
          assert: result
          equals:
              (Dictionary new
                  add: 'direction' -> 'south';
                  add:
                      'position'
                          ->
                              (Dictionary new
                                  add: 'x' -> 0;
                                  add: 'y' -> 0;
                                  yourself);
                  yourself)
  
  
  but I cannot come to the same outcome with this code : 
  
  
  pointToName:
aPoint
    ^aPoint x
isZero
   ifTrue: 
[aPoint y > 0 ifTrue: [#north] ifFalse: [#south]]
   ifFalse:
[aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]


maybe exercism.io is not a good
way to practice and learn smalltalk but I found not a
better one. or smalltalk is not for me. 

Roelof






  
  
  
  
  
  
  Op 8-4-2019 om 16:44 schreef 

Re: [Pharo-users] difference between double dispatch and the method explains here

[Richard O'Keefe]

You are expected to use my code fragments for *ideas*,
not to incorporate them *literally* in your code.  As
I explained, *without seeing the specification*, I have
no way to tell whether the specification uses a left-handed
or right-handed coordinate system.

For what it's worth, here's a complete program in my
Smalltalk dialect.  It doesn't plug into the exercism
testing framework because I can do not know what it
looks like.  But if it makes the code more complicated
that this, it's doing it wrong.

require: 'geometry.st'  "Point"
require: 'print.st' "OutputStream>>print:"

Object subclass: #Robot
  instanceVariableNames: 'position direction'
  poolDirectionaries:'FileStream'

  methods for: 'initialising'
pvtPostNew
  position  := 0@0.
  direction := 1@0.

  methods for: 'accessing'
direction
  ^direction copy

location
  ^location copy

obey: commands
  commands do: [:each |
each caseOf: {
  [$A] -> [position  := position  + direction].
  [$L] -> [direction := direction leftRotated].
  [$R] -> [direction := direction rightRotated]
}].

  class methods for: 'main'
start
  [StdIn atEnd] whileFalse: [
 |robot|
 robot := Robot new.
 Robot obey: StdIn nextLine.
 StdOut print: Robot location; cr].

On Tue, 9 Apr 2019 at 02:58, Roelof Wobben  wrote:

> yes,  this is a real  tests from the pharo track on exercism.io
>
> I understand what you mean but maybe I overthinking things.
> But if we have a robot facing north and the robot turns to the left  , im
> my oponion it faces now to the east.
>
> like this test is saying :
>
>
> test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth
> | result |
> result := robotSimulatorCalculator
> moveDirection: 'east'
> position:
> (Dictionary new
> add: 'x' -> 0;
> add: 'y' -> 0;
> yourself)
> instructions: 'R'.
> self
> assert: result
> equals:
> (Dictionary new
> add: 'direction' -> 'south';
> add:
> 'position'
> ->
> (Dictionary new
> add: 'x' -> 0;
> add: 'y' -> 0;
> yourself);
> yourself)
>
>
> but I cannot come to the same outcome with this code :
>
>
> pointToName: aPoint
>   ^aPoint x isZero
>  ifTrue:  [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]]
>  ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
>
>
> maybe exercism.io is not a good way to practice and learn smalltalk but I
> found not a better one. or smalltalk is not for me.
>
> Roelof
>
>
>
>
>
>
>
>
>
>
>
> Op 8-4-2019 om 16:44 schreef Richard O'Keefe:
>
> The basic issue here is abstraction.
> An instance of "Robot" in your program is not a
> physical object.  How could it possibly point North,
> South, or Nor-nor-west?  It cannot.
> Its location and direction are abstract values
> *metaphorically* related to real world notions
> like position vectors and velocity vectors.
> "North" in this program is not a real thing,
> it is an *idea* which could be represented by
> 'North', 'north', #North, #north, $N, $n,
> 'Raki',  'raki',  #Raki,  #raki,  $R, $r,
> 137, (0@ -1), a picture of the star Polaris,
> the colour red (the conventional colour for
> that end of a compass needle which points north),
> a sound recording of a lecture by Alfred North
> Whitehead, or anything you please, as long as,
> inside the program, it *acts* the way *you* want
> "north" to act (which is not necessarily the way
> the physical direction North acts, and in fact in
> this case it most certainly is not).
>
> Locations and movements in a 2D space are, in Smalltalk,
> commonly represented by Points.  "Represented by."
>
> As for this method:
>
>
> test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth
> | result |
> result := robotSimulatorCalculator
> moveDirection: 'north'
> position:
> (Dictionary new
> add: 'x' -> 0;
> add: 'y' -> 0;
> yourself)
> instructions: 'A'.
> self
> assert: result
> equals:
> (Dictionary new
> add: 'direction' -> 'north';
> add:
> 'position'
> ->
> (Dictionary new
> add: 'x' -> 0;
> add: 'y' -> 1;
> yourself);
> yourself)
>
> PLEASE tell me that is not what they are actually using.
> Let's start with
>   (Dictionary new)
>  add: k1 -> v1;
>  ...
>  add: kn -> vn;
>  yourself
> Did you know that 

Re: [Pharo-users] difference between double dispatch and the method explains here

[Roelof Wobben]

  
  
yes,  this is a real  tests from the
  pharo track on exercism.io
  
  I understand what you mean but maybe I overthinking things. 
  But if we have a robot facing north and the robot turns to the
  left  , im my oponion it faces now to the east. 
  
  like this test is saying : 
  
test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth
      | result |
      result := robotSimulatorCalculator
          moveDirection: 'east'
          position:
              (Dictionary new
                  add: 'x' -> 0;
                  add: 'y' -> 0;
                  yourself)
          instructions: 'R'.
      self
          assert: result
          equals:
              (Dictionary new
                  add: 'direction' -> 'south';
                  add:
                      'position'
                          ->
                              (Dictionary new
                                  add: 'x' -> 0;
                                  add: 'y' -> 0;
                                  yourself);
                  yourself)
  
  
  but I cannot come to the same outcome with this code : 
  
  
  pointToName:
aPoint
   
^aPoint x isZero
  
ifTrue:  [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]]
  
ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]


maybe exercism.io is not a good way to practice and learn
smalltalk but I found not a better one. or smalltalk is not for
me. 

Roelof






  
  
  
  
  
  
  Op 8-4-2019 om 16:44 schreef Richard O'Keefe:


  
  
The basic issue here
  is abstraction.
An instance of "Robot"
  in your program is not a
physical object.  How
  could it possibly point North,
South, or
  Nor-nor-west?  It cannot.
Its location and
  direction are abstract values
*metaphorically*
  related to real world notions
like position vectors
  and velocity vectors.
"North" in this
  program is not a real thing,
it is an *idea* which
  could be represented by
'North', 'north',
  #North, #north, $N, $n,
'Raki',  'raki', 
  #Raki,  #raki,  $R, $r,
137, (0@ -1), a
  picture of the star Polaris,
the colour red (the
  conventional colour for
that end of a compass
  needle which points north),
a sound recording of a
  lecture by Alfred North
Whitehead, or anything
  you please, as long as,
inside the program, it
  *acts* the way *you* want
"north" to act (which
  is not necessarily the way
the physical direction
  North acts, and in fact in
this case it most
  certainly is not).


Locations and
  movements in a 2D space are, in Smalltalk,
commonly represented
  by Points.  "Represented by."


As for this method:


test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth
      | result |
      result := robotSimulatorCalculator
          moveDirection: 'north'
          position:
              (Dictionary new
                  add: 'x' -> 0;
                  add: 'y' -> 0;
                  yourself)
          instructions: 'A'.
      self
          assert: result
          equals:
              (Dictionary new
                  add: 'direction' -> 'north';
                  add:
                      'position'
                          ->
                              (Dictionary new
                                  add: 'x' -> 0;
                                  add: 'y' -> 1;
                                  yourself);
                  yourself)


PLEASE tell me that is
  not what they are actually using.
Let's start with
  (Dictionary new)
 add: k1 -> v1;
 ...
 add: kn -> vn;
 yourself
Did you know that
  sending #add: to a dictionary is not
portable?  Storing
  actual Association objects inside
Dictionaries was
  originally an encapsulation error and
remains a performance
  error, so there are Smalltalks
that do not make that
  mistake.  The *portable* way to
make a Dictionary is
    

Re: [Pharo-users] difference between double dispatch and the method explains here

[Richard O'Keefe]

The basic issue here is abstraction.
An instance of "Robot" in your program is not a
physical object.  How could it possibly point North,
South, or Nor-nor-west?  It cannot.
Its location and direction are abstract values
*metaphorically* related to real world notions
like position vectors and velocity vectors.
"North" in this program is not a real thing,
it is an *idea* which could be represented by
'North', 'north', #North, #north, $N, $n,
'Raki',  'raki',  #Raki,  #raki,  $R, $r,
137, (0@ -1), a picture of the star Polaris,
the colour red (the conventional colour for
that end of a compass needle which points north),
a sound recording of a lecture by Alfred North
Whitehead, or anything you please, as long as,
inside the program, it *acts* the way *you* want
"north" to act (which is not necessarily the way
the physical direction North acts, and in fact in
this case it most certainly is not).

Locations and movements in a 2D space are, in Smalltalk,
commonly represented by Points.  "Represented by."

As for this method:

test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth
| result |
result := robotSimulatorCalculator
moveDirection: 'north'
position:
(Dictionary new
add: 'x' -> 0;
add: 'y' -> 0;
yourself)
instructions: 'A'.
self
assert: result
equals:
(Dictionary new
add: 'direction' -> 'north';
add:
'position'
->
(Dictionary new
add: 'x' -> 0;
add: 'y' -> 1;
yourself);
yourself)

PLEASE tell me that is not what they are actually using.
Let's start with
  (Dictionary new)
 add: k1 -> v1;
 ...
 add: kn -> vn;
 yourself
Did you know that sending #add: to a dictionary is not
portable?  Storing actual Association objects inside
Dictionaries was originally an encapsulation error and
remains a performance error, so there are Smalltalks
that do not make that mistake.  The *portable* way to
make a Dictionary is
(Dictionary new)
   at: k1 put: v1;
   ...
   at: kn put: vn;
   yourself.

And why in the name of sanity are the keys *strings*
instead of *symbols*?  This is not Smalltalk.  It is
Javascript in drag.

Now exercism.io has a habit of insisting on particular
implementations.  For example, I completed the SML track,
and found that the test code ONLY worked with Poly and
not with any of the three SML implementations I already
had on my machine.  Since you are doing this in Pharo,
I take it that exercism.io will insist on the Smalltalk
track being done in Pharo, and in that case it is
*nauseating* to use a Dictionary when you could use a
Point.  Old-fashioned Smalltalk style would have been
to return something like
   #(  )
e.g. #(north 1 0), and I still prefer that.

In fact *good* Smalltalk style for something like this
would be
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth
  robotSimulatorCalculator
moveTo: 0@0;
head: #north;
obey: 'A'.
  self assert: robotSimulatorCalculator heading equals: #north.
  self assert: robotSimulatorCalculator location equals: 0@1.

-- We're starting to get the idea that identifiers like
robotSimulatorCalculator are not a very good idea when
simulatedRobot would do the job as well or better.

(This is also pointing us towards Betrand Meyer's
Command/Query Separation principle, but we shan't
go there today.)

This is important feedback to give to the exercism.io
people.  The test code should use a SMALLTALK interface,
not a warmed-over JAVASCRIPT interface.

Now, how do we map between direction *names* and
direction *points*?  Well, we have to start by
laying down clearly what we *mean* by the directions.

To move North one step is to add 1 to y and 0 to x.
(We know that from the appalling test case above.)
To move South one step is to add -1 to y and 0 to x.
(South is the opposite of North.)
To move East one step, oh we have a problem.
THIS NEEDS SPELLING OUT.  And one of the things the
exercism.io exercises are HORRIBLY BAD AT is specifying
the problem.  Nearly every single exercise I have tried,
I have been unable to tell what the problem is without
examining the test cases, and that is not the way
exercises are supposed to work.  (Yeah, that's why I'm
screaming about it.  I've taught a class using exercises
like this that were not of my writing and vague specifications
really upset the students.  People who had taken the class
under someone else several years before were still angry
about it.)

The geometric classes in Smalltalk were written to support
graphic user interfaces.  And in user interfaces, the y
coordinate increases DOWN.  So if we take the compass rose
and rotate it so that North is 

Re: [Pharo-users] difference between double dispatch and the method explains here

[Roelof Wobben]

  
  
Richard thanks. 
  
  One thing I do not see direct. 
  
  you said : 
  
  
  
  A
direction could be represented by a pair of integers
  dx,
dy such that |dx|+|dy| = 1.  It could also be
  represented
by a Point with integer components.

for me a direction is the direction the robot is facing so
something like north or east. 

the challenge also wants a output like this : 

test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth
    | result |
    result := robotSimulatorCalculator
        moveDirection: 'north'
        position:
            (Dictionary new
                add: 'x' -> 0;
                add: 'y' -> 0;
                yourself)
        instructions: 'A'.
    self
        assert: result
        equals:
            (Dictionary new
                add: 'direction' -> 'north';
                add:
                    'position'
                        ->
                            (Dictionary new
                                add: 'x' -> 0;
                                add: 'y' -> 1;
                                yourself);
                yourself)

so how do I "convert" the point you are using to the text. 

Or do I misunderstood you somewhere wrong. 

Roelof

  
  
  
  
  Op 8-4-2019 om 10:57 schreef Richard O'Keefe:


  
  
One thing I have often
  seen and lamented is students
writing excessively
  complicated code with way too many
classes.  There is a
  huge difference between
  "A Robot knows its
  position and direction."
and
  "A Robot has-a
  Position and has-a Direction."
The first is the
  important one.  The second is
an over-commitment to
  too many classses.  For a
problem like this, you
  really really do not want
a Direction class, and
  you certainly have no use
for double dispatch.


A position can be
  represented by a pair of integers
x, y.  It could also
  be represented by a Point with
integer components.


A direction could be
  represented by a pair of integers
dx, dy such that
  |dx|+|dy| = 1.  It could also be
represented by a Point
  with integer components.


For movement, you need
  to be able to add the direction
to the location, which
  could be simply
x := x + dx.  y := y +
  dy.
or it could be
position := position +
  direction.
For turning, you need
  to be able to rotate a direction
vector by ninety
  degrees.  Now it so happens that
Point has methods
  #leftRotated and #rightRotated.


So we can do the
  following:
   a Robot has
  position (a Point) and direction (aPoint)
   position := 0 @ 0.
   direction := 0 @ 1.
To move forward
  without turning:
   position :=
  position + direction.
To turn left without
  moving:
   direction :=
  direction leftRotated.
To turn right without
  moving:
   direction :=
  direction rightRotated.
To obey a sequence of
  characters, commands:
   commands do: [:each
  |
  each caseOf: {
 [$A] ->
  [--move forward--].
 [$L] ->
  [--turn left--].
 [$R] ->
  [--turn right--]
  }].




One of the key ideas
  in extreme programming is
"You Ain't Gonna Need
  It", abbreviated to YAGNI!
The idea is *DON'T*
  generalise beyond your immediate
needs.  In this case,
  for example, the likelihood of
*this* program needing
  to deal with more general
kinds of movement is
  ZERO.  And the only reason for
using Point here
  instead of just using a few simple
assignment statements
  is that Point already exists,
so costs nothing to
  write, and as a familiar class,
code using it should
  be easy to read.



If someone challenges
  you to do something counter-productive,
refuse the challenge.

  
  
  
On Mon, 8 Apr 2019 at 17:21,
  Roelof 

Re: [Pharo-users] difference between double dispatch and the method explains here

[Roelof Wobben]

  
  
Op 8-4-2019 om 10:57 schreef Richard
  O'Keefe:


  
  
One thing I have often
  seen and lamented is students
writing excessively
  complicated code with way too many
classes.  There is a
  huge difference between
  "A Robot knows its
  position and direction."
and
  "A Robot has-a
  Position and has-a Direction."
The first is the
  important one.  The second is
an over-commitment to
  too many classses.  For a
problem like this, you
  really really do not want
a Direction class, and
  you certainly have no use
for double dispatch.


A position can be
  represented by a pair of integers
x, y.  It could also
  be represented by a Point with
integer components.


A direction could be
  represented by a pair of integers
dx, dy such that
  |dx|+|dy| = 1.  It could also be
represented by a Point
  with integer components.


For movement, you need
  to be able to add the direction
to the location, which
  could be simply
x := x + dx.  y := y +
  dy.
or it could be
position := position +
  direction.
For turning, you need
  to be able to rotate a direction
vector by ninety
  degrees.  Now it so happens that
Point has methods
  #leftRotated and #rightRotated.


So we can do the
  following:
   a Robot has
  position (a Point) and direction (aPoint)
   position := 0 @ 0.
   direction := 0 @ 1.
To move forward
  without turning:
   position :=
  position + direction.
To turn left without
  moving:
   direction :=
  direction leftRotated.
To turn right without
  moving:
   direction :=
  direction rightRotated.
To obey a sequence of
  characters, commands:
   commands do: [:each
  |
  each caseOf: {
 [$A] ->
  [--move forward--].
 [$L] ->
  [--turn left--].
 [$R] ->
  [--turn right--]
  }].




One of the key ideas
  in extreme programming is
"You Ain't Gonna Need
  It", abbreviated to YAGNI!
The idea is *DON'T*
  generalise beyond your immediate
needs.  In this case,
  for example, the likelihood of
*this* program needing
  to deal with more general
kinds of movement is
  ZERO.  And the only reason for
using Point here
  instead of just using a few simple
assignment statements
  is that Point already exists,
so costs nothing to
  write, and as a familiar class,
code using it should
  be easy to read.



If someone challenges
  you to do something counter-productive,
refuse the challenge.

  
  
  
On Mon, 8 Apr 2019 at 17:21,
  Roelof Wobben  wrote:


  
I
  can try to explain what I trying to solve. 
  
  I have a Robot which can turn left,  turn right or
  moveForward. 
  
  now I have a string like 'LAR'
  
  that means the robot needs to turn left (l) , move forward
  one place (A) and turn left. 
  and I have to keep track to which direction the robot is
  facing and on which coordinate it stands. 
  
  so to summarize with the above string 
  
  lets say the robot is facing north on coordinate (0,0) 
  then it has to turn left , so its facing east and still on
  coordinate (0,0) 
  then it has to move forward, so its still  facing east but
  are on coordinate(0,1) 
  then it has to turn right, so its facing north and on
  coordinate (0,1) 
  
  and TimMacKinnon has challenged me to do this with double
  dispatch. 
  
  So I think now I need a object Direction, a sub object
  North and a sub - sub object TurnLeft, turnRight and
  moveForward. 
  
  So I can use double dispath first the direction North,
  East, South, West 
  and then use double dispatch to find the right move. 
  
  Roelof
  
  
  
  
  
  

Re: [Pharo-users] difference between double dispatch and the method explains here

[Richard O'Keefe]

One thing I have often seen and lamented is students
writing excessively complicated code with way too many
classes.  There is a huge difference between
  "A Robot knows its position and direction."
and
  "A Robot has-a Position and has-a Direction."
The first is the important one.  The second is
an over-commitment to too many classses.  For a
problem like this, you really really do not want
a Direction class, and you certainly have no use
for double dispatch.

A position can be represented by a pair of integers
x, y.  It could also be represented by a Point with
integer components.

A direction could be represented by a pair of integers
dx, dy such that |dx|+|dy| = 1.  It could also be
represented by a Point with integer components.

For movement, you need to be able to add the direction
to the location, which could be simply
x := x + dx.  y := y + dy.
or it could be
position := position + direction.
For turning, you need to be able to rotate a direction
vector by ninety degrees.  Now it so happens that
Point has methods #leftRotated and #rightRotated.

So we can do the following:
   a Robot has position (a Point) and direction (aPoint)
   position := 0 @ 0.
   direction := 0 @ 1.
To move forward without turning:
   position := position + direction.
To turn left without moving:
   direction := direction leftRotated.
To turn right without moving:
   direction := direction rightRotated.
To obey a sequence of characters, commands:
   commands do: [:each |
  each caseOf: {
 [$A] -> [--move forward--].
 [$L] -> [--turn left--].
 [$R] -> [--turn right--]
  }].


One of the key ideas in extreme programming is
"You Ain't Gonna Need It", abbreviated to YAGNI!
The idea is *DON'T* generalise beyond your immediate
needs.  In this case, for example, the likelihood of
*this* program needing to deal with more general
kinds of movement is ZERO.  And the only reason for
using Point here instead of just using a few simple
assignment statements is that Point already exists,
so costs nothing to write, and as a familiar class,
code using it should be easy to read.

If someone challenges you to do something counter-productive,
refuse the challenge.

On Mon, 8 Apr 2019 at 17:21, Roelof Wobben  wrote:

> I can try to explain what I trying to solve.
>
> I have a Robot which can turn left,  turn right or moveForward.
>
> now I have a string like 'LAR'
>
> that means the robot needs to turn left (l) , move forward one place (A)
> and turn left.
> and I have to keep track to which direction the robot is facing and on
> which coordinate it stands.
>
> so to summarize with the above string
>
> lets say the robot is facing north on coordinate (0,0)
> then it has to turn left , so its facing east and still on coordinate
> (0,0)
> then it has to move forward, so its still  facing east but are on
> coordinate(0,1)
> then it has to turn right, so its facing north and on coordinate (0,1)
>
> and TimMacKinnon has challenged me to do this with double dispatch.
>
> So I think now I need a object Direction, a sub object North and a sub -
> sub object TurnLeft, turnRight and moveForward.
>
> So I can use double dispath first the direction North, East, South, West
> and then use double dispatch to find the right move.
>
> Roelof
>
>
>
>
>
> Op 8-4-2019 om 06:50 schreef Richard O'Keefe:
>
> It would really REALLY **REALLY** help if we knew what
> the heck you were trying to do.  There is an excellent
> chance that it is MUCH simpler than you think.  If you
> cannot show us the Smalltalk version of the problem,
> can you show us the version for some other language?
>
>
> On Sun, 7 Apr 2019 at 20:15, Roelof Wobben  wrote:
>
>> Op 6-4-2019 om 15:15 schreef K K Subbu:
>> > On 06/04/19 4:49 PM, Roelof Wobben wrote:
>> >> Hello,
>> >>
>> >> I just learned double dispatch.
>> >> And now for the Robot challenge of exercism Tim has pointed me to
>> >> this
>> >> article(
>> https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
>>
>> >>
>> >> but I fail to see how the move method looks like in that article.
>> >> I had a conversation with Tim in the exercism channel and the way he
>> >> explains it, it looks like double dispatch for me.
>> >>
>> >> Am I on the right track or do I oversee something here.
>> > unary methods like moveRight perform specific ops and are not
>> > parametric, so only a single dispatch, depending on the receiver, is
>> > needed.
>> >
>> > If you change it to move: aDistanceOrAngle, then performing requests
>> > like "move: 3 cms" or "move: 30 degrees" will depend not only on the
>> > receiver but also on the class of the argument. This would need double
>> > dispatch (aka multiple polymorphism). The first dispatch would be
>> > based on the receiver and the receiver's method would then dispatch it
>> > based on the class of the argument (i.e. Distance>>move or Angle>>move )
>> >
>> > HTH .. Subbu
>> >
>> >
>>
>>
>> hmm, still stuck
>>
>> I have now a class Direction with as 

Re: [Pharo-users] difference between double dispatch and the method explains here

[Roelof Wobben]

  
  
I can try to explain what I trying to
  solve. 
  
  I have a Robot which can turn left,  turn right or moveForward. 
  
  now I have a string like 'LAR'
  
  that means the robot needs to turn left (l) , move forward one
  place (A) and turn left. 
  and I have to keep track to which direction the robot is facing
  and on which coordinate it stands. 
  
  so to summarize with the above string 
  
  lets say the robot is facing north on coordinate (0,0) 
  then it has to turn left , so its facing east and still on
  coordinate (0,0) 
  then it has to move forward, so its still  facing east but are on
  coordinate(0,1) 
  then it has to turn right, so its facing north and on coordinate
  (0,1) 
  
  and TimMacKinnon has challenged me to do this with double
  dispatch. 
  
  So I think now I need a object Direction, a sub object North and a
  sub - sub object TurnLeft, turnRight and moveForward. 
  
  So I can use double dispath first the direction North, East,
  South, West 
  and then use double dispatch to find the right move. 
  
  Roelof
  
  
  
  
  
  Op 8-4-2019 om 06:50 schreef Richard O'Keefe:


  
  
It would really REALLY
  **REALLY** help if we knew what
the heck you were
  trying to do.  There is an excellent
chance that it is MUCH
  simpler than you think.  If you
cannot show us the
  Smalltalk version of the problem,
can you show us the
  version for some other language?


  
  
  
On Sun, 7 Apr 2019 at 20:15,
  Roelof Wobben  wrote:

Op
  6-4-2019 om 15:15 schreef K K Subbu:
  > On 06/04/19 4:49 PM, Roelof Wobben wrote:
  >> Hello,
  >>
  >> I just learned double dispatch.
  >> And now for the Robot challenge of exercism Tim has
  pointed me to 
  >> this 
  >> article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
  
  >>
  >> but I fail to see how the move method looks like in
  that article.
  >> I had a conversation with Tim in the exercism channel
  and the way he 
  >> explains it, it looks like double dispatch for me.
  >>
  >> Am I on the right track or do I oversee something
  here.
  > unary methods like moveRight perform specific ops and are
  not 
  > parametric, so only a single dispatch, depending on the
  receiver, is 
  > needed.
  >
  > If you change it to move: aDistanceOrAngle, then
  performing requests 
  > like "move: 3 cms" or "move: 30 degrees" will depend not
  only on the 
  > receiver but also on the class of the argument. This
  would need double 
  > dispatch (aka multiple polymorphism). The first dispatch
  would be 
  > based on the receiver and the receiver's method would
  then dispatch it 
  > based on the class of the argument (i.e.
  Distance>>move or Angle>>move )
  >
  > HTH .. Subbu
  >
  >
  
  
  hmm, still stuck
  
  I have now a class Direction with as instance variables north,
  south, 
  east, west
  and made the accessors.
  
  then I thought I need a initialize like this :
  
  initialize
      north = Direction( 0, -1).
      east  = Direction( 1,  0).
      south = Direction( 0,  1).
      west  = Direction(-1,  0).
  
  but the Direction (0,-1)  is a problem . the compiler does not
  like the 
  (0,-1) part
  
  to give you the big picture. I have a Robot which can
  turnRight , 
  turnLeft and moveForward and I try to understand how the page
  would work 
  in my case.
  
  So I have a object Direction as described above and a Object
  MoveForward 
  which is a subobject of Direction.
  MoveForward has only 1 method :
  
  IsMove
      ^  'A'
  
  Roelof
  
  

  


  

Re: [Pharo-users] difference between double dispatch and the method explains here

[Richard O'Keefe]

It would really REALLY **REALLY** help if we knew what
the heck you were trying to do.  There is an excellent
chance that it is MUCH simpler than you think.  If you
cannot show us the Smalltalk version of the problem,
can you show us the version for some other language?


On Sun, 7 Apr 2019 at 20:15, Roelof Wobben  wrote:

> Op 6-4-2019 om 15:15 schreef K K Subbu:
> > On 06/04/19 4:49 PM, Roelof Wobben wrote:
> >> Hello,
> >>
> >> I just learned double dispatch.
> >> And now for the Robot challenge of exercism Tim has pointed me to
> >> this
> >> article(
> https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
>
> >>
> >> but I fail to see how the move method looks like in that article.
> >> I had a conversation with Tim in the exercism channel and the way he
> >> explains it, it looks like double dispatch for me.
> >>
> >> Am I on the right track or do I oversee something here.
> > unary methods like moveRight perform specific ops and are not
> > parametric, so only a single dispatch, depending on the receiver, is
> > needed.
> >
> > If you change it to move: aDistanceOrAngle, then performing requests
> > like "move: 3 cms" or "move: 30 degrees" will depend not only on the
> > receiver but also on the class of the argument. This would need double
> > dispatch (aka multiple polymorphism). The first dispatch would be
> > based on the receiver and the receiver's method would then dispatch it
> > based on the class of the argument (i.e. Distance>>move or Angle>>move )
> >
> > HTH .. Subbu
> >
> >
>
>
> hmm, still stuck
>
> I have now a class Direction with as instance variables north, south,
> east, west
> and made the accessors.
>
> then I thought I need a initialize like this :
>
> initialize
> north = Direction( 0, -1).
> east  = Direction( 1,  0).
> south = Direction( 0,  1).
> west  = Direction(-1,  0).
>
> but the Direction (0,-1)  is a problem . the compiler does not like the
> (0,-1) part
>
> to give you the big picture. I have a Robot which can turnRight ,
> turnLeft and moveForward and I try to understand how the page would work
> in my case.
>
> So I have a object Direction as described above and a Object MoveForward
> which is a subobject of Direction.
> MoveForward has only 1 method :
>
> IsMove
> ^  'A'
>
> Roelof
>
>
>

Re: [Pharo-users] difference between double dispatch and the method explains here

[Roelof Wobben]

Op 6-4-2019 om 15:15 schreef K K Subbu:

On 06/04/19 4:49 PM, Roelof Wobben wrote:

Hello,

I just learned double dispatch.
And now for the Robot challenge of exercism Tim has pointed me to 
this 
article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html) 


but I fail to see how the move method looks like in that article.
I had a conversation with Tim in the exercism channel and the way he 
explains it, it looks like double dispatch for me.


Am I on the right track or do I oversee something here.
unary methods like moveRight perform specific ops and are not 
parametric, so only a single dispatch, depending on the receiver, is 
needed.


If you change it to move: aDistanceOrAngle, then performing requests 
like "move: 3 cms" or "move: 30 degrees" will depend not only on the 
receiver but also on the class of the argument. This would need double 
dispatch (aka multiple polymorphism). The first dispatch would be 
based on the receiver and the receiver's method would then dispatch it 
based on the class of the argument (i.e. Distance>>move or Angle>>move )


HTH .. Subbu





hmm, still stuck

I have now a class Direction with as instance variables north, south, 
east, west

and made the accessors.

then I thought I need a initialize like this :

initialize
   north = Direction( 0, -1).
   east  = Direction( 1,  0).
   south = Direction( 0,  1).
   west  = Direction(-1,  0).

but the Direction (0,-1)  is a problem . the compiler does not like the 
(0,-1) part


to give you the big picture. I have a Robot which can turnRight , 
turnLeft and moveForward and I try to understand how the page would work 
in my case.


So I have a object Direction as described above and a Object MoveForward 
which is a subobject of Direction.

MoveForward has only 1 method :

IsMove
   ^  'A'

Roelof

Re: [Pharo-users] difference between double dispatch and the method explains here

[Roelof Wobben]

  
  
oke, 
  
  so I need a single Object here 
  that contains this in a initialize function : 
  
  north = Direction( 0, -1)
east  = Direction( 1,  0)
south = Direction( 0,  1)
west  = Direction(-1,  0)



oke, then time to figure out how to change my functions because I have the feeling that I still miss
some of the pieces: 

Robot >> move: aInstruction
	aInstruction = $R
		ifTrue: [ ^ self direction: (PositioningSystem new turnRight: direction) ].
	aInstruction = $L
		ifTrue: [ ^ self direction: (PositioningSystem new turnLeft: direction) ].
	^ self
		position:
			(PositioningSystem new moveForWard: position direction: self direction)




  PositionSystem class >>  initialize
      Directions := {('north' -> (0 @ 1)).
      ('east' -> (1 @ 0)).
      ('south' -> (0 @ -1)).
      ('west' -> (-1 @ 0))}
  
  PositionSystem >> turnRight: aDirection
      "comment stating purpose of message"
  
      | old |
      old := Directions detect: [ :b | b key = aDirection ].
      ^ (Directions after: old ifAbsent: [ Directions first ]) key
  
  Roelof
  
  
  
  
  
  Op 6-4-2019 om 15:15 schreef K K Subbu:

On
  06/04/19 4:49 PM, Roelof Wobben wrote:
  
  Hello,


I just learned double dispatch.

And now for the Robot challenge of exercism Tim has pointed me
to this
article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)

but I fail to see how the move method looks like in that
article.

I had a conversation with Tim in the exercism channel and the
way he explains it, it looks like double dispatch for me.


Am I on the right track or do I oversee something here.

  
  unary methods like moveRight perform specific ops and are not
  parametric, so only a single dispatch, depending on the receiver,
  is needed.
  
  
  If you change it to move: aDistanceOrAngle, then performing
  requests like "move: 3 cms" or "move: 30 degrees" will depend not
  only on the receiver but also on the class of the argument. This
  would need double dispatch (aka multiple polymorphism). The first
  dispatch would be based on the receiver and the receiver's method
  would then dispatch it based on the class of the argument (i.e.
  Distance>>move or Angle>>move )
  
  
  HTH .. Subbu
  
  
  


  

Re: [Pharo-users] difference between double dispatch and the method explains here

[K K Subbu]

On 06/04/19 4:49 PM, Roelof Wobben wrote:

Hello,

I just learned double dispatch.
And now for the Robot challenge of exercism Tim has pointed me to this 
article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html) 


but I fail to see how the move method looks like in that article.
I had a conversation with Tim in the exercism channel and the way he 
explains it, it looks like double dispatch for me.


Am I on the right track or do I oversee something here.
unary methods like moveRight perform specific ops and are not 
parametric, so only a single dispatch, depending on the receiver, is needed.


If you change it to move: aDistanceOrAngle, then performing requests 
like "move: 3 cms" or "move: 30 degrees" will depend not only on the 
receiver but also on the class of the argument. This would need double 
dispatch (aka multiple polymorphism). The first dispatch would be based 
on the receiver and the receiver's method would then dispatch it based 
on the class of the argument (i.e. Distance>>move or Angle>>move )


HTH .. Subbu