Just here to point out that the actor’s name is Bob Odenkirk not Odendirk. In a statically typed language this would be an error at compile time not hacker news comment time.
The Trade-offs section doesn't list the biggest one.
Secretly, all code wants to be spaghetti. You and your team have to put a conscious effort into prevent that from happening. Degrading the core of the language like this is like inoculating your homebrew with sewage and expecting it not to go wrong.
(defn better-cond
[& pairs]
(fn [& arg]
(label result
(defn argy [f] (if (> (length arg) 0) (f ;arg) (f arg))) # naming is hard
(each [pred body] (partition 2 pairs)
(when (argy pred)
(return result (if (function? body)
(argy body) # calls body on args
body)))))))
Most Lisps have `cond` like this:
(def x 5)
(cond
((odd? x) "odd") ; note wrapping around each test-result pair
((even? x) "even"))
Clojure (and children Fennel and Janet) don't require wrapping the pairs:
(def x 5)
(cond
(odd? x) "odd"
(even? x) "even")
My combinatoresque `better-cond` doesn't require a variable at all and is simply a function call which you can `map` over etc.:
((better-cond
(fn [x] (> 3 x)) "not a number" # just showing that it can accept other structures
odd? "odd"
even? "even") 5)
Of course, it can work over multiple variables too and have cool function output:
(defn recombine # 3 train in APL or ϕ combinator
[f g h]
(fn (& x) (f (g ;x) (h ;x))))
(((better-cond
|(function? (constant ;$&))
|($ array + -)) recombine) 1 2) # |( ) is Janet's short function syntax with $ as vars
Do you have any recommendations for a language where you _have to_ use these concepts. I love playing with them but I find that unless i’m paying a lot of attention in most cases I fall back to a less functional style even in a language like Janet. I’d love to find a language where you largely have to use these combinatorial logic style functions so I can’t just default back to other styles.
Forth, Factor and Uiua (which combines the above approach) don't use these concepts yet are also inherently point-free, and without lambdas so you definitely wouldn't be able to rely on functional techniques!
For lambda calculus, the motto is "when everything is a function".
The boolean true is the function λx.λy.x, while false is λx.λy.y.
If b then x else y then simply becomes b x y.
In a functional language like Haskell that is basically a typed lambda calculus with lots of syntactic sugar, we can replicate this with:
type MyBool a = a -> a -> a
myTrue :: MyBool a
myTrue = \x y -> x
myFalse :: MyBool a
myFalse = \x y -> y
myIf :: MyBool a -> a -> a -> a
myIf b myThen myElse = b myThen myElse
main = print $ myIf myTrue "true" "false"
Interesting that this article makes no mention of eager vs lazy evaluation - isn’t a big reason that if, for etc has to be special forms in an eagerly evaluated language that their arguments need to be lazily evaluated, which of course, deviates from the rule?
Also, lazy evaluation is achieved in an eagerly evaluated language as simply wrapping a block of code in a function, which makes lazy evaluation isomorphic with the contents of the article
> You might wonder: “Won’t the block execute immediately when passed as an argument?” Here’s the key insight: in Rye, code blocks { ... } are values. They don’t evaluate until you explicitly tell them to.
When everything is an expression, like rust (I think), that's enough. Most of the control flow are used as statements, but if needed, they can be used directly as expression, and you get basically all the advantages. After seeing how effective this is, using a language that doesn't have this feature can be really annoying.
On the other hand, I would like to explore "when arithmetics is just a function". I think Elm does this well: operators are just functions with two arguments that can be written as "1 + 2", the familiar way, or "(+) 1 2". Then you can compose it like "map ((+) 2)" (currying) so you get a function that adds 2 to every item of a list, and so on.
I'm definitely missing some key insight because after reading the article I felt it was a strawman argument.
Python already has conditional expressions, which already allow 'x if (predicate) else y'. Therefore in Python if is already equivalent to a function, and is composable.
Once you realize this, and also understand that Python has logical operators that can short-circuit, all Python examples feel convoluted and required the blogger to go way out of it's way to write nonidiomatic Python. If the goal was to make a point with Python, why not write Python?
Python was used as an example because people know Python and reader can compare it to something known.
I wasn't trying to make Python look awkward. I was trying to write equivalent Python, you are very much welcome to suggest improvements to my Python examples.
Other languages could be used instead of Python, for example Javascript. But I feel Python is more contained language, with clear ways to do thing (I guess I don't know them that well :) )
The drawback is that this approach elevates code blocks to first class. It means that there is a semantical difference between a value that is a block and a value that is a result of a block. This reduces code clarity, because now block def/result is discriminated by context instead of syntax.
- closures get tricky, i.e. having outer scoped variables within a block
- inter-block operators still need special care, e.g. return should return from a function or a nearest block, same for break/continue/etc.
This criticism seems at face value to also apply to first-class functions, which I thought was a totally uncontroversial pattern. Do you dislike those too?
This is interesting, but I'm not convinced it's better than the python it's being compared to. Memorizing and understanding the behavior of functions that perform control flow seems no easier than memorizing and understanding hardcoded syntax/keywords. The additional flexibility of making everything a first-class citizen allows people to write code that is too clever for its own good. I could be wrong but I think there is a broad consensus that reflection is a Bad Idea.
Open to being convinced otherwise
(tangent but related, aren't the "Loops" and "Iteration" examples given for python literally the exact same syntax, with the exception of changing how the iterable is generated?)
> I could be wrong but I think there is a broad consensus that reflection is a Bad Idea.
Reflection may be bad in practice for other reasons/conditions, but the lack of simple/minimal/regular primitive conventions in many languages, makes reflection a basket of baddies.
The code blocks of Rye seem comparable to closures, which is a sensible thing to have. Once all code blocks are closures, there are fewer concepts to wrangle, and functional control makes excellent sense.
It depends on what you want. If you want the most stabile and predictable way to specify the behavior, then static control structures have little downsides.
If you want to explore with how you can specify behaviors or rules and create new options or the ones tightly fitting your problem domain or mental model, then this gives you more tools to do so.
You may not want a fresh scope for control flow as you often want to use variables from the outer scope inside the if statement. Imagine you wanted to do something like this with your if statement implemented with a function (this is how the syntax would look like using a block argument in Ruby):
state = "inactive"
if_func(condition) {
state = "active"
activate_button.disabled = true
deactivate_button.disabled = false
}
In many languages you would need to wrap `state` in something that can be passed by reference, and make the function take multiple parameters. For example in JavaScript it would turn into something like this mess:
You can define its recursion principle by building a higher-order function that receives an element of your type and, for each constructor, receives a function that takes all the parameters of that constructor (with any recursive parameters replaced by `r`) and returns `r`.
For `List` this becomes:
foldr :: (() -> r) -> (a -> r -> r) -> List a -> r
The eliminator for `Nil` can be simplified to `r` as `() -> r` is isomorphic to `r`:
foldr :: r -> (a -> r -> r) -> List a -> r
foldr z f Nil = z
foldr z f (List a xs) = f a (foldr f z xs)
For `Bool`:
data Bool = True | False
We get:
bool :: a -> a -> Bool -> a
bool p q True = q
bool p q False = p
I don't know a lot about Tcl, but one thing I know is said for it "everything is a string". In REBOL's it's somewaht reverse as all this live code are REBOL (Rye) values and REBOL (and Rye) have an unusual number of datatypes, REBOL 30+ (many literal types), which it uses as additional information for functions to work with, and is usefull at creating dialects
For example file-path, url and email address are distinct types in REBOL where in mosta languages are just strings.
Yeah, here. They should know the feeling of booleans as instances and ifTrue: ifFalse: as methods. But for us is such an obvious thing that isn't really something too remarkable. It normalized language awesomeness.
It's only a problem if I have my browser set to use dark theme or system theme and my system theme is dark if I switch it to light theme. Everything looks good. So most likely he's using some kind of CSS framework that's automatically responding to the dark theme, but other styles that he's hand coded are not compatible with it
I checked in Firefox and Chrome (on Linux) and code samples look OK to me. What browser/OS are you using. Maybe send me a screenshot at janko dot itm at gmail.
$vau is similar to $lambda, except it doesn't implicitly evaluate its operands, and it implicitly receives it's caller's dynamic environment as a first class value which gets bound to env.
$lambda is not actually a builtin in Kernel, but wrap is, which constructs an applicative by wrapping an operative.
I wish they showed the `else` syntax, because the traditional ALGOL-style if-then-else statement doesn't look native when shoved into most function call notations, unless you have something pretty interesting around named parameters and expressions delimiters.
there is no if { } else { } in REBOL or Rye and it wouldn't really fit. There is either function that accepts two code blocks. It can act as a typical if / else or as a ternary expression as it also returns the result of a block:
BTW: In Lisps, if is still a special form / macro, because in Lisp lists are evaluated by default, in Rebols if can be a function because blocks (lists) aren't evaluated by default.
Now about the point about Lisps and if: the regular if operator with value and expression arguments has a companion if function:
4> (special-operator-p 'if)
t
5> (fboundp 'if)
t
Unlike in some other dialects like Common Lisp, a symbol can have a binding in the macro or operator space, and in the function space at the same time.
But this if is not useful control. It's useful for things like being able to map over a function-like facsimile of the if operator. E.g. take an element of the (a b c d) or (x y z w) list depending on whether the leftmost list has a nil or t:
6> [mapcar if '(nil t nil t) '(a b c d) '(x y z w)]
(x b z d)
In the reverse direction, being able to write a macro for a function function exists, allows for ordinary macros to be "compiler macros" in the Common Lisp sense: provide optimizations for certain invocations of a function.
This dialect is not even "weird"; overall it is Common-Lisp-like. Right down to the multiple namespaces, which is why the [...] syntax exists for referring to functions and variables in a combined virtual namespace.
I checked the Rye homepage, and it has "dialects" which allow more familiar math infix notation. In that sense it is very tcl-y, tcl technically being a lisp.
Looking at their rather confusing looping mechanisms, they probably could benefit from being a little more tcl-y, since tcl has some of the best looping semantics I've worked with.
I can tell the rye devs like the idea of everything being a function. But in their very first "language basics" section, they introduce assignment not as a function call, but as some kind of magic that happens when you have colons in a name.
So when we get to the "looping" section, it is the first time we have seen a colon-having-name outside the context of assignment:
> loop 3 { ::i , prns i }
And it is explained that the above line of code is "injecting" values for the code block to "pick up".
But right away this begs a number of questions:
* Why the double-colon? I would assume each loop-body-evaluation happens in its own scope, and that we're not creating global variables, so a single colon (:i) should be sufficient, right?
* What are we doing, conceptually? Is the ::i meant to be "a function which when given a value modifies its enclosing scope to include the symbol i" or "an unassigned symbol which the loop function will use to do something akin to term-rewriting with?"
* Do we really need a symbol at all, or could we just have a the point-free loop "loop 3 {prns}"?
* If we can't have the point free thing, is it because somehow the injected value would end up "to the left" of prns, if so, why would we want that?
* If we're doing something more like term rewriting, why isn't the symbol given as a separate argument from the body?
Rye is foremost a REBOL and REBOL has this notion of many types of words at it's core:
`word` - regular word, can evaluate to value it's bound to or call a funtion if bound to a function
`word: "value"` - set-word, assignment that you noticed
`probe :word` - get-word, always returns bound value, doesn't call a function if it's bound to a function, in Rye this is `?word`, because `:word` is left-set-word.
`'word` - literal word, evaluates to a word itself
etc ...
Rye adds even more word types. Rye also has left to right flow so it adds left-set-word. In Rye all assigned words with set-words are constants and they are used by default. So we also need a "mod-word", that is the double colon that you noticed, and left-mod-word. Because of left-to-right flow Rye also has .op-words and |pipe-words.
The logic around words, op-words and pipe-words ... I tried to explain here:
Another pattern you noticed (good observation btw:) is the idea of injected blocks that isn't used just for loops, but also for conditionals, function bodies, HOF-like functions etc ...
> Rye also has left to right flow so it adds left-set-word. In Rye all assigned words with set-words are constants and they are used by default. So we also need a "mod-word", that is the double colon that you noticed, and left-mod-word
So I would assume that the :i is actually constant within the loop body scope. That is, the loop function is doing something like this:
; i is not assigned in this scope
evaluate {1 :i, prns i}
evaluate {2 :i, prns i}
evaluate {3 :i, prns i}
; i is still not assigned in this scope
But it sounds like you're telling me that :i would actually escape the scope of the loop body and so it needs to be modifiable or else the loop will break.
Yes, Rye follows REBOL in this case. Plain block invocation doesn't create it's own scope / context. That holds for do, if, either, loop, for, map, etc.
It would be costly to have this on by default. If you want separation there are many ways to achieve it. Rye has many functions related to contexts / scopes. For creating contexts in multiple ways and evaluating code inside contexts or with context as parent or isolated context, etc.
And a lot of builtins directly accept anonymous functions in place of blocks of code.
For example for loop also accepts function if you want separation and don't mind the cost.
for { 1 2 3 } fn { x } { print x }
; which can also be written with fn1
for { 1 2 3 } fn1 { .print }
; or latest experiment where we have syntax for 3 injected blocks
; .() - same as "with"
; .[] - same as "reduce/with"
; .{} - same as "fn1"
; where it's already decided department from REBOL:
; () is "do"
; [] is "vals"
; {} is literal block
for { 1 2 3 } .{ .print }
If you treat assignment as a function, then you have to reify environments as run-time objects, whereby you basically lose lexical scope.
Lisp originally, as in LISP, had assignment as a function: it was called SET.
To use it, you usually had to quote: (SET 'VAR 42).
It worked without an environment parameter because variables were in a pervasive environment, but the quote was needed to get the variable symbol as a run-time value. (SET VAR 42)
would mean evaluate VAR to a symbol, and then pass that symbol to the SET function along with 42, so whatever variable was in VAR would be assigned.
Assignment is inherently non-functional, since it is a side-effect, so it is mostly counterproductive to model it as a function.
A pattern matching or logical language can have implicit bindings as the results of an operation, and so produce variables that way. Then instead of assignment you have shadowing, in that some construct binds a variable again that was already used, so that the most recent value then emerges, shadowing the previous one.
So tcl handles it somewhat more elegantly, I think. It also has a set function, but does not require any special quoting because it uses the $ prefix to denote "get the value of this symbol":
set a 5
puts $a #prints 5
and of course because it is modeled as a function (albeit an impure one) you can pass arguments to it as normal:
set a b
set $a 5 #equivalent to set b 5
puts $b #prints 5
of course, everything in tcl is a string, so this works too lol
I’ve personally always thought that REBOL’s use of set-words and similar constructs was a strength. It makes sense conceptually, is visually distinguishable, and maintains a strong sense of internal consistency.
REBOL (and by extension, Rye) was never designed around the idea that everything must be a function. It just turns out that this approach fits naturally within the core principles and rules of the language.
All “active” words happen to be functions, because nothing else is needed. The behavior of different word types (and, more broadly, value types) is determined by the evaluator. In that sense, you could say that Rye does have syntax, expressed through its distinct word types.
This discussion makes me so happy because people still care about programming languages and not just on stupid Java or whatever is making gobs of money. LISP should have a much larger following than it does, though I fully admit it has its own warts.
Just here to point out that the actor’s name is Bob Odenkirk not Odendirk. In a statically typed language this would be an error at compile time not hacker news comment time.
The Trade-offs section doesn't list the biggest one.
Secretly, all code wants to be spaghetti. You and your team have to put a conscious effort into prevent that from happening. Degrading the core of the language like this is like inoculating your homebrew with sewage and expecting it not to go wrong.
Combinatory programing offers functional control flow. (Here is a straight forward explanation: https://blog.zdsmith.com/series/combinatory-programming.html ) I was inspired to write `better-cond` in Janet:
Do you have any recommendations for a language where you _have to_ use these concepts. I love playing with them but I find that unless i’m paying a lot of attention in most cases I fall back to a less functional style even in a language like Janet. I’d love to find a language where you largely have to use these combinatorial logic style functions so I can’t just default back to other styles.
J and BQN (APL has off-ramps...)
https://code.jsoftware.com/wiki/Essays/Tacit_Expressions
https://mlochbaum.github.io/BQN/doc/tacit.html and https://mlochbaum.github.io/BQN/doc/control.html
Forth, Factor and Uiua (which combines the above approach) don't use these concepts yet are also inherently point-free, and without lambdas so you definitely wouldn't be able to rely on functional techniques!
[dead]
For lambda calculus, the motto is "when everything is a function". The boolean true is the function λx.λy.x, while false is λx.λy.y. If b then x else y then simply becomes b x y. In a functional language like Haskell that is basically a typed lambda calculus with lots of syntactic sugar, we can replicate this with:
Interesting that this article makes no mention of eager vs lazy evaluation - isn’t a big reason that if, for etc has to be special forms in an eagerly evaluated language that their arguments need to be lazily evaluated, which of course, deviates from the rule? Also, lazy evaluation is achieved in an eagerly evaluated language as simply wrapping a block of code in a function, which makes lazy evaluation isomorphic with the contents of the article
> You might wonder: “Won’t the block execute immediately when passed as an argument?” Here’s the key insight: in Rye, code blocks { ... } are values. They don’t evaluate until you explicitly tell them to.
You're correct, that is lazy evaluation. The entire article talks about lazy evaluation without mentioning it, which was my point
When everything is an expression, like rust (I think), that's enough. Most of the control flow are used as statements, but if needed, they can be used directly as expression, and you get basically all the advantages. After seeing how effective this is, using a language that doesn't have this feature can be really annoying.
On the other hand, I would like to explore "when arithmetics is just a function". I think Elm does this well: operators are just functions with two arguments that can be written as "1 + 2", the familiar way, or "(+) 1 2". Then you can compose it like "map ((+) 2)" (currying) so you get a function that adds 2 to every item of a list, and so on.
I'm definitely missing some key insight because after reading the article I felt it was a strawman argument.
Python already has conditional expressions, which already allow 'x if (predicate) else y'. Therefore in Python if is already equivalent to a function, and is composable.
Once you realize this, and also understand that Python has logical operators that can short-circuit, all Python examples feel convoluted and required the blogger to go way out of it's way to write nonidiomatic Python. If the goal was to make a point with Python, why not write Python?
Python was used as an example because people know Python and reader can compare it to something known.
I wasn't trying to make Python look awkward. I was trying to write equivalent Python, you are very much welcome to suggest improvements to my Python examples.
Other languages could be used instead of Python, for example Javascript. But I feel Python is more contained language, with clear ways to do thing (I guess I don't know them that well :) )
The drawback is that this approach elevates code blocks to first class. It means that there is a semantical difference between a value that is a block and a value that is a result of a block. This reduces code clarity, because now block def/result is discriminated by context instead of syntax.
- closures get tricky, i.e. having outer scoped variables within a block
- inter-block operators still need special care, e.g. return should return from a function or a nearest block, same for break/continue/etc.
This criticism seems at face value to also apply to first-class functions, which I thought was a totally uncontroversial pattern. Do you dislike those too?
First-class functions are problematic too[1], but function is always a definition. While code block is usually meant to be executed right away.
[1]: https://github.com/ziglang/zig/issues/1048
This is interesting, but I'm not convinced it's better than the python it's being compared to. Memorizing and understanding the behavior of functions that perform control flow seems no easier than memorizing and understanding hardcoded syntax/keywords. The additional flexibility of making everything a first-class citizen allows people to write code that is too clever for its own good. I could be wrong but I think there is a broad consensus that reflection is a Bad Idea.
Open to being convinced otherwise
(tangent but related, aren't the "Loops" and "Iteration" examples given for python literally the exact same syntax, with the exception of changing how the iterable is generated?)
> I could be wrong but I think there is a broad consensus that reflection is a Bad Idea.
Reflection may be bad in practice for other reasons/conditions, but the lack of simple/minimal/regular primitive conventions in many languages, makes reflection a basket of baddies.
The code blocks of Rye seem comparable to closures, which is a sensible thing to have. Once all code blocks are closures, there are fewer concepts to wrangle, and functional control makes excellent sense.
That makes sense, thanks!
It depends on what you want. If you want the most stabile and predictable way to specify the behavior, then static control structures have little downsides.
If you want to explore with how you can specify behaviors or rules and create new options or the ones tightly fitting your problem domain or mental model, then this gives you more tools to do so.
I agree. In any somewhat functional language (I.e. all the mainstream ones) you can wrap "if" in a function if you please.
E.g.
If you want to do clever stuff. I never feel the need as I would rather abstract over bigger things.You may not want a fresh scope for control flow as you often want to use variables from the outer scope inside the if statement. Imagine you wanted to do something like this with your if statement implemented with a function (this is how the syntax would look like using a block argument in Ruby):
In many languages you would need to wrap `state` in something that can be passed by reference, and make the function take multiple parameters. For example in JavaScript it would turn into something like this mess:You can do it, but that is not how the (default) control structures work in those languages. There is usually also some syntax cost.
Thats a good point. Idiomatics are important and not following them makes incompatible code.
Given an algebraic data type such as:
You can define its recursion principle by building a higher-order function that receives an element of your type and, for each constructor, receives a function that takes all the parameters of that constructor (with any recursive parameters replaced by `r`) and returns `r`.For `List` this becomes:
The eliminator for `Nil` can be simplified to `r` as `() -> r` is isomorphic to `r`: For `Bool`: We get: Which is precisely an If statement as a function!:D
Seems a bit like Tcl, which lets you create your own control structures like that.
I don't know a lot about Tcl, but one thing I know is said for it "everything is a string". In REBOL's it's somewaht reverse as all this live code are REBOL (Rye) values and REBOL (and Rye) have an unusual number of datatypes, REBOL 30+ (many literal types), which it uses as additional information for functions to work with, and is usefull at creating dialects
For example file-path, url and email address are distinct types in REBOL where in mosta languages are just strings.
Or redefine the language provided 'if' statement, in the case that one wanted to do so.
You can't really redefine if because everything is a constant, but you can define if in your own context yes.
In Tcl you can redefine "if", or even delete it entirely if you're crazy enough :-)
Smalltalk, anyone? I guess the OO version.
Yeah, here. They should know the feeling of booleans as instances and ifTrue: ifFalse: as methods. But for us is such an obvious thing that isn't really something too remarkable. It normalized language awesomeness.
There is a language https://sprylang.se/index.html which started more as Rebol and moved towards Smalltalk.
Interestingly, Excel provides "if" as a function:
=if(condition, value-if-true, value-if-false)
Yes, Io language is closest to that syntax probably:
https://iolanguage.org/guide/guide.html#Introduction
I wonder if it's more readable to non-programmers than control flow.
That's because Excel is a pure functional language :-)
https://www.youtube.com/watch?v=0yKf8TrLUOw
Is this just a quirk in my display, or are all the code blocks in this formatted like a CIA black highlighter
It's only a problem if I have my browser set to use dark theme or system theme and my system theme is dark if I switch it to light theme. Everything looks good. So most likely he's using some kind of CSS framework that's automatically responding to the dark theme, but other styles that he's hand coded are not compatible with it
I checked in Firefox and Chrome (on Linux) and code samples look OK to me. What browser/OS are you using. Maybe send me a screenshot at janko dot itm at gmail.
Same here. I guess it's an issue with (system) dark theme (you can simulate that in dev tools. Android here, so must be Chrome.
I fixed it thanks! I was able to activate dark more in Firefox on desktop and find problems with CSS.
Thank you all for heads up! I was playing with CSS and didn't test the dark mode. I think it's fixed now.
Useless unless the logical operators receive their rhs unevaluated. And that is generalized as a language feature.
A general language feature would be fexprs, or call-by-name (which can be combined with call-by-value using call-by-push-value).
In Kernel[1] for example, where operatives are an improved fexpr.
$vau is similar to $lambda, except it doesn't implicitly evaluate its operands, and it implicitly receives it's caller's dynamic environment as a first class value which gets bound to env.$lambda is not actually a builtin in Kernel, but wrap is, which constructs an applicative by wrapping an operative.
All functions have an underlying operative which can be extracted with unwrap.[1]:https://ftp.cs.wpi.edu/pub/techreports/pdf/05-07.pdf
I wish they showed the `else` syntax, because the traditional ALGOL-style if-then-else statement doesn't look native when shoved into most function call notations, unless you have something pretty interesting around named parameters and expressions delimiters.
See the `either` function further down
there is no if { } else { } in REBOL or Rye and it wouldn't really fit. There is either function that accepts two code blocks. It can act as a typical if / else or as a ternary expression as it also returns the result of a block:
This is Rebol's doc on either, Rye's works exactly the same: https://www.rebol.com/docs/words/weither.htmlI own the 'if' package on npm, which I wrote to be functions that can replace the if keyword, making no use of the if keyword in its definition.
interesting. Give us an example of it's usage ... or how you implemented it?
I looked at the code - it uses ternary expressions.
Seems lispy
BTW: In Lisps, if is still a special form / macro, because in Lisp lists are evaluated by default, in Rebols if can be a function because blocks (lists) aren't evaluated by default.
You can rarely successfully generalize about languages in the Lisp family. :)
TXR Lisp: (relevant to this article) there is an iff function that takes functional arguments.
Square the odd values in 0 to 9:
The use function is a synonym of identity: i.e. just use the incoming value as-isSquare the even ones instead by inverting oddp with notf:
Get rid of use with iffi: a two-argument iff with an implicit identity else: Now about the point about Lisps and if: the regular if operator with value and expression arguments has a companion if function: Unlike in some other dialects like Common Lisp, a symbol can have a binding in the macro or operator space, and in the function space at the same time.But this if is not useful control. It's useful for things like being able to map over a function-like facsimile of the if operator. E.g. take an element of the (a b c d) or (x y z w) list depending on whether the leftmost list has a nil or t:
In the reverse direction, being able to write a macro for a function function exists, allows for ordinary macros to be "compiler macros" in the Common Lisp sense: provide optimizations for certain invocations of a function.This dialect is not even "weird"; overall it is Common-Lisp-like. Right down to the multiple namespaces, which is why the [...] syntax exists for referring to functions and variables in a combined virtual namespace.
What's the benefit of being implemented as lisp-2 but acting like lisp-1 with [ ]? Why not just be a lisp-1?
> TXR is an original notation for matching entire text documents or streams, inspired by the unification that underlies logic programming systems
This has me hooked.
I checked the Rye homepage, and it has "dialects" which allow more familiar math infix notation. In that sense it is very tcl-y, tcl technically being a lisp.
Looking at their rather confusing looping mechanisms, they probably could benefit from being a little more tcl-y, since tcl has some of the best looping semantics I've worked with.
Any concrete feedback on looping mechanisms being confusing is appreciated.
Certainly:
I can tell the rye devs like the idea of everything being a function. But in their very first "language basics" section, they introduce assignment not as a function call, but as some kind of magic that happens when you have colons in a name.
So when we get to the "looping" section, it is the first time we have seen a colon-having-name outside the context of assignment:
> loop 3 { ::i , prns i }
And it is explained that the above line of code is "injecting" values for the code block to "pick up".
But right away this begs a number of questions:
* Why the double-colon? I would assume each loop-body-evaluation happens in its own scope, and that we're not creating global variables, so a single colon (:i) should be sufficient, right?
* What are we doing, conceptually? Is the ::i meant to be "a function which when given a value modifies its enclosing scope to include the symbol i" or "an unassigned symbol which the loop function will use to do something akin to term-rewriting with?"
* Do we really need a symbol at all, or could we just have a the point-free loop "loop 3 {prns}"?
* If we can't have the point free thing, is it because somehow the injected value would end up "to the left" of prns, if so, why would we want that?
* If we're doing something more like term rewriting, why isn't the symbol given as a separate argument from the body?
Rye is foremost a REBOL and REBOL has this notion of many types of words at it's core:
`word` - regular word, can evaluate to value it's bound to or call a funtion if bound to a function
`word: "value"` - set-word, assignment that you noticed
`probe :word` - get-word, always returns bound value, doesn't call a function if it's bound to a function, in Rye this is `?word`, because `:word` is left-set-word.
`'word` - literal word, evaluates to a word itself
etc ...
Rye adds even more word types. Rye also has left to right flow so it adds left-set-word. In Rye all assigned words with set-words are constants and they are used by default. So we also need a "mod-word", that is the double colon that you noticed, and left-mod-word. Because of left-to-right flow Rye also has .op-words and |pipe-words.
The logic around words, op-words and pipe-words ... I tried to explain here:
https://ryelang.org/meet_rye/specifics/opwords/
Another pattern you noticed (good observation btw:) is the idea of injected blocks that isn't used just for loops, but also for conditionals, function bodies, HOF-like functions etc ...
https://ryelang.org/meet_rye/specifics/injected_blocks/
All in all it is supposed to be a compact set of ideas that fit together. Some are somewhat unusual.
> Rye also has left to right flow so it adds left-set-word. In Rye all assigned words with set-words are constants and they are used by default. So we also need a "mod-word", that is the double colon that you noticed, and left-mod-word
So I would assume that the :i is actually constant within the loop body scope. That is, the loop function is doing something like this:
; i is not assigned in this scope
evaluate {1 :i, prns i}
evaluate {2 :i, prns i}
evaluate {3 :i, prns i}
; i is still not assigned in this scope
But it sounds like you're telling me that :i would actually escape the scope of the loop body and so it needs to be modifiable or else the loop will break.
Yes, Rye follows REBOL in this case. Plain block invocation doesn't create it's own scope / context. That holds for do, if, either, loop, for, map, etc.
It would be costly to have this on by default. If you want separation there are many ways to achieve it. Rye has many functions related to contexts / scopes. For creating contexts in multiple ways and evaluating code inside contexts or with context as parent or isolated context, etc.
And a lot of builtins directly accept anonymous functions in place of blocks of code.
For example for loop also accepts function if you want separation and don't mind the cost.
If you treat assignment as a function, then you have to reify environments as run-time objects, whereby you basically lose lexical scope.
Lisp originally, as in LISP, had assignment as a function: it was called SET.
To use it, you usually had to quote: (SET 'VAR 42).
It worked without an environment parameter because variables were in a pervasive environment, but the quote was needed to get the variable symbol as a run-time value. (SET VAR 42) would mean evaluate VAR to a symbol, and then pass that symbol to the SET function along with 42, so whatever variable was in VAR would be assigned.
Assignment is inherently non-functional, since it is a side-effect, so it is mostly counterproductive to model it as a function.
A pattern matching or logical language can have implicit bindings as the results of an operation, and so produce variables that way. Then instead of assignment you have shadowing, in that some construct binds a variable again that was already used, so that the most recent value then emerges, shadowing the previous one.
So tcl handles it somewhat more elegantly, I think. It also has a set function, but does not require any special quoting because it uses the $ prefix to denote "get the value of this symbol":
and of course because it is modeled as a function (albeit an impure one) you can pass arguments to it as normal: of course, everything in tcl is a string, so this works too lolI’ve personally always thought that REBOL’s use of set-words and similar constructs was a strength. It makes sense conceptually, is visually distinguishable, and maintains a strong sense of internal consistency.
REBOL (and by extension, Rye) was never designed around the idea that everything must be a function. It just turns out that this approach fits naturally within the core principles and rules of the language.
All “active” words happen to be functions, because nothing else is needed. The behavior of different word types (and, more broadly, value types) is determined by the evaluator. In that sense, you could say that Rye does have syntax, expressed through its distinct word types.
Without the discussion of applicative-order versus normal-order.
This discussion makes me so happy because people still care about programming languages and not just on stupid Java or whatever is making gobs of money. LISP should have a much larger following than it does, though I fully admit it has its own warts.