[squeak-dev] Monads in Squeak

Kjell Godo squeaklist at gmail.com
Thu Aug 4 06:45:04 UTC 2022

so what is the use of a Monad anyway if you are not lazy
     is my question

well it is supposed to isolate state changes ?
     or simulate state or what is it

you’ve got the state Monad
     so every time you are going to mutate state you stop short ?
     you do not mutate the state no
     you make a new state like consing a new cons cell onto a list
     which is not state
          or something
     and you return that new cons cell
so every time you would have mutated the state you do not mutate
     the state no you do the state Monad shuffle instead

but often in the GUI you want the dependents to get the latest value
     of a variable and you don’t care about the old value or
     well it’s confusing

so i am drawn to this whole Monad idea
     maybe somehow it simplifies or something
     i feel like maybe it does but when i look i can’t really see it
     i can’t really see why     if you are not lazy
     i want to see it but i keep coming up short

On Wed, Aug 3, 2022 at 23:17 Kjell Godo <squeaklist at gmail.com> wrote:

> probably
> Association class>>inClass:c return:anObject
>      ^( ( anObject isKindOf:c )
>             ifTrue:[ self key:c value:anObject ]
>             itFalse:[ self error:’wrong type’ ] )
> would be the best place to do the type check
> so now Associations are Monads or Association subClass:#Monad or whatever
> so then
> Association>>=<< a1InputValua
>      ^( self class inClass:( self key )return:( a1InputValua value:( self
> value ) ) )
> On Wed, Aug 3, 2022 at 22:53 Kjell Godo <squeaklist at gmail.com> wrote:
>> correct me if i am wrong but
>> Association class>>return: anObject ^( self new value: anObject )
>> Association>>=<< aOneInputValua
>>      ^( self class return:( aOneInputValua value:( self value ) ) )
>> where
>>      ( aOneInputValua respondsTo:#value: )=true
>> or
>> Association class>>inClass:c return: anObject ^( self key:c value:
>> anObject )
>> Association>>=<< a2InputValua
>>      ^( self class inClass:( self key )return:(
>>              aOneInputValua value:( self key )value:( self value ) ) )
>>              “where aOneInputValua uses its first input which is aClass
>> to do some
>>                kind of runtime type checking or like
>> or maybe more like”
>> Association class>>inClass:c return: anObject ^( self key:c value:
>> anObject )
>> Association>>=<< a1InputValua
>>      ^( self class inClass:( self key )return:(
>>           a1InputValua value:(
>>                ( ( self value )isKindOf:( self key ) )
>>                     ifTrue:[ self value ]ifFlase:[ self Error:’wrong
>> type’ ] ) ) )
>> you see the thing about Haskell is that it is completely lazy so there is
>> no evaluation ordering that can be counted on so monads are a way to impose
>> an execution order via function composition like
>> ( h value:( g value:( f value: x ) ) ) forces f to be done first and h
>> last and g second
>> but Smalltalk is not lazy , so there is a runtime ordering , so maybe
>> Smalltalk can get an equivalent functionality out of just composing one
>> input valua which is just composing one input functions , unless you want
>> to insist on the >>isKindOf: type checking
>> On Wed, Aug 3, 2022 at 15:18 Eliot Miranda <eliot.miranda at gmail.com>
>> wrote:
>>> Hi Tony,
>>> On Mon, Aug 1, 2022 at 1:48 AM Tony Garnock-Jones <
>>> tonyg at leastfixedpoint.com> wrote:
>>>> On the Squeak Slack, @asarch asked "Are there monads in Squeak?"
>>>> My answer was:
>>>> Tricky question. Monads are a kind of design pattern reflecting a
>>>> formal
>>>> mathematical structure. Languages with static type systems are able to
>>>> enforce some (but usually not all) of the mathematical monad laws; in
>>>> Smalltalk, the type system is not strong enough to enforce any monad
>>>> laws. So, monads do appear in Smalltalk in two ways: implicitly, in
>>>> that
>>>> theoretically every expression is "in the IO monad"; and explicitly, in
>>>> examples such as the API on class Promise. Squeak's Promise class
>>>> implements monadic operations and honours the monad laws.
>>> I'd love to read a definition of the monad laws in plain English.  I
>>> think I understand promises perfectly well.  I've never understood what a
>>> monad is.  I'm unable to think algebraically very effectively but can think
>>> visually (for example I didn't understand the fourier transform
>>> algebraically (the double integral formulation), but understand it
>>> perfectly well as an infinite set of infinite integrals of the products of
>>> a sine wave with an arbitrary waveform (itself composed of sine waves)).
>>> So if you can explain monads without recourse to algebra (but as much
>>> recourse to Smalltalk as you like) then you have my full attention.
>>> So TL;DR is "yes, but..." :-)
>>>> Cheers,
>>>>    Tony
>>> _,,,^..^,,,_
>>> best, Eliot
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