Smalltalk, Haskell and Lisp

It looks OK to me:

    (define (time-to-move from-pos to-pos)
      ;; Calculates the total time to move between two positions,
      ;; assuming rotation and ascension can occur simultaneously.
      (max (time-to-rotate (position-azimuth   from-pos)
                           (position-azimuth   to-pos))
           (time-to-ascend (position-elevation from-pos)
                           (position-elevation to-pos))))

    (defun time-to-move (from-pos to-pos)

    (with-slots (last-duration) antenna
      (setf last-duration total-time)

    (setf (last-duration antenna) total-time)  ;; given last-duration is an accessor: both a getter and a setter.

  (defun run-scan (antenna scan)
    "Perform a scan on this antenna. Return a scan log."
    (let* ((slew-time (move-to antenna (scan-position scan)))
           (on-source-time (delay antenna (scan-length scan))))
      (setf (antenna-last-duration antenna) (+ on-source-time slew-time))
      (make-scan-log scan slew-time on-source-time)))

There's a lot in this article that I really identify with: the preference for a functional style (even if I'm just not smart enough to do the whole ultra-abstract symbol soup Haskell thing); the comfort I feel leaning on the compiler; "it also always feels like I’m tricking Lisp into doing what I want, rather than simply expressing what I want" feels like it came right from my brain.

God, Lisp...the core language isn't exactly that interesting in this day-and-age. Dynamic typing, garbage collection, anonymous functions, this has been the bread-and-butter of Python, JS, Ruby, etc. developers for like 20 years now. It's got some really powerful features like conditions and CLOS. But then the bulk of the language and library built on top is such a mess: it's missing so much basic functionality, but also has so many niche functions that can be configured every which way with niche keyword arguments, and they all turned out to be evolutionary dead-ends and much worse than what the rest of the world settled on (actually CLOS probably falls into this category too). I think it's this, more than anything, that makes programming in Lisp feel like an act of trickery rather than clear thinking.

But I'll also say that I've been hobby programming in Lisp a bit recently and, despite that, I've been finding it immensely pleasurable, the first time I've really enjoyed working with a computer in years. The highly interactive, image-based workflow is just so much smoother than my day job, where I'm constantly jumping between VSCode and Chrome and a console and manually rebuilding and sitting around waiting...

Macros may be a double-edged sword - they encourage monstrosities like LOOP, rather than building more powerful/regular/comprehensible language features like iterators or comprehensions. BUT when paired with that interactive development experience, it really feels like you're in a dialogue with the computer, building out a little computational universe.

  ; A comment
  (set-macro-character #\% (get-macro-character #\;))
  % Also a comment

The Smalltalk implementation is off. Scan is a verb not a noun and I think the readability the author was seeking would be more plain by sending messages to an antenna to ask it to move it's position and report back it's scan times and such.

Oooo, such pretty solutions here. What do people think of this APL option?

    (destEl-sourceEl)⌈destAz-sourceAz

Honestly, though, we don't really know what any of the reference implementations do. The core structure structure is just (max (f x y) (g z w)), and we have to simply guess at the meaning of f and g by their names. The above APL takes a similar liberty, but instead of a fiat declaring, we just a fiat declare that our data is sufficiently normalized.

Here's my take on performScan, too:

    Log⍪←onSourceTime+slewTime

    ⌈/dest-source

> This almost doesn’t look like code to me. I would expect any programmer to be able to at least get some sense of what’s going on here, even without knowing Haskell. I don’t think I could say the same thing about this piece of Lisp:

I only understand the Haskell code as well as I do because the comment describes what it does (much more clearly than the docstring on the lisp function). Others have already posted about how unnecessarily verbose the lisp function is, so I won't rehash that part here.

> I got to see first-hand that notions like function calling, sequential processing, and boolean logic are not intuitive

It was a very long time since I first learned programming.

It was QBasic first I think.

It was a very slow process that I had mostly forgotten.

It took me a very long time to grasp what's now very basic control flow.

But I was like 7 or 10.

I remember feeling like "this is pure magic!" so many times so very early on.

Part of what I want to do is rekindle that like pico8 did for me. Somehow.

I honestly expected the article to start like

Smalltalk, Haskell, and Lisp

...walk into a bar.

Smalltalk: “Bartender, please send an instance of Martini to me - selector withOlive: set to true.”

Haskell: “I’ll take beer >>= chill, but only if it’s defined for all inputs and returns IO ().”

Lisp: “(drink ’(ale (temperature cold))) .”

The bartender mutters, “Great ... an object, a functor, and a list.”

Then a janitor walks by sweeping the closures that they left.

2011

The epiphany I had with haskell was understanding why it was so modular. It goes beyond just understanding haskell though and towards understanding the fundamental nature of modularity.

Think about it. What is the smallest most primitive computation that is modular?

If you have a method that mutates things, then that method is tied to the thing it mutates and everything else that mutates it. You can't move a setter away from the entity it mutates without moving the entity with it. It's not modular.

What about an IO function? Well for an IO function to work it must be tied to the IO. Is it a SQL database? A chat client? If you want to move the IO function you have to move the IO it is intrinsically tied with.

So what is the fundamental unit of computation? The pure function. A function that takes an input and returns an output deterministically. You can move that thing anywhere and it is also the smallest computation possible in a computer.

The reason why haskell is so modular is it forces you to segregate away IO and purity. The type system automatically forces you to make the code using the most modular primitives possible. It's almost like how rust forces you to code in a way that prevents certain errors.

Your code in haskell will be made entirely of "pure" functions with things touching IO being segregated away via the IO monad. There is no greater form of modularity and decoupling.

In fact any other computing primitive you use in your program will inevitably be LESS modular then a pure function. That's why when you're programming with OOP or imperative or any other style of programming you'll always hit more points where modularity is broken then you would say haskell. That is not to say perfect modularity is the end goal, but if it was the path there is functional programming.

Ugh, now I want to pick up F# again. I like and identify with many points about Haskell but F# fits like a glove for our ecosystem here.

The problem with using objects and structs in Common Lisp is the verbosity of access, or of setting up shorter access using with-slots and with-accessors.

I fixed that in TXR Lisp:

  (defun time-to-move (from-pos to-pos)
     (max (time-to-rotate from-pos.azimuth to-pos.azimuth)
          (time-to-ascend from-pos.elevation to-pos.elevation)))

The remaining issues are self-inflicted verbose naming. I would make it

  ;; time to move
  (defun ttm (p0 p1)
    (max (ttr p0.az p1.az)
         (tta p0.el p1.el)))

If the entire program fits on a few pages, you can remember a few abbreviations.

The dot notation is a syntactic sugar for certain S-exps:

  a.b.(c x y).d   ->   (qref a b (c x y) d)

  .a.b.c          ->   (uref a b c)

there exist macros by these names which take care of the rest.

Starting in TXR 300, there can be whitespace after the dot. So while you cannot write in in the popular way:

  obj
  .(meth arg)
  .(next-meth 42)

you can do it like this:

  obj.
  (meth arg).
  (next-meth 42)

this has a lot do with Lisp already having a consing dot.

Lisp doesn't mean being against all syntactic sugars; e.g. we mostly write 'X rather than (quote 'X).

But note that even if we don't have this notation, how the author has tripped over himself to create verbosity. After two nestings of with-accessors he ends up with:

  (time-to-rotate from-az to-az) (time-to-ascend from-el to-el)

Here from-az is not a whole lot shorter than (az from)! If he used shorter names like el and az, he would have:

  (defun time-to-move (from to)
    (max (time-to-rotate (az p0) (az p1))
         (time-to-ascend (el p0) (el l1))))

Don't make names for yourself that you then have to shorten with clumsy macros that make the function longer overall.

Another thing is, why does time-to-move take two objects? But time-to-rotate and time-to-ascend work with destructured azimuths and elevations?

  (defun time-to-move (from to)
    (max (time-to-rotate from to)
         (time-to-ascend from to)))

Time to rote and time to ascend could be inseparable. If the device is mounted on an incline, the time to ascend may depend on the azimuth. It may be better to rotate it first than elevate or vice versa, or execute some optimal combined motion.

The moment of inertia of the thing may depend on its elevation; it may be easier to rotate in a high elevation. So just time-to-rotate alone needs the whole object.

Smalltalk used to have left arrow for assignment like I see in the Haskell here.

It's a lot prettier than :=

    b _ 5

    b ← 5

    b := 5

IDK. They all look a little atrocious to me.

But readability has a lot to do with what you are used to.

The only exception might be FORTH. A very well written FORTH implementation (and I mean very well written) probably would be fairly readable to anyone — at least at the higher levels of abstraction.