noonien (Nov 20 2023 at 16:19): noonien (Nov 20 2023 at 16:19):how can a function that has no parameters be defined? from what i can tell from the tutorial, values become functions when either they have parameters, or call other functions. am I misunderstanding something?
Brendan Hansknecht (Nov 20 2023 at 16:23):It can't. The normal convention is to pass an empty record to the function.
Brendan Hansknecht (Nov 20 2023 at 16:23):So it still has one argument
noonien (Nov 20 2023 at 16:24):interesting
Richard Feldman (Nov 20 2023 at 16:24):it should be a very rare use case, since Roc functions can't have side effects :big_smile:
Brendan Hansknecht (Nov 20 2023 at 16:24):Simple example from builtins: https://www.roc-lang.org/builtins/Dict#empty
noonien (Nov 20 2023 at 16:25):well, with no side effects, it would basically be useless, but I'm wondering what happens when calling platform functions that do have side effects
noonien (Nov 20 2023 at 16:25):maybe something like getting the environment variables
noonien (Nov 20 2023 at 16:25):or something simpler, like getting the time
Brendan Hansknecht (Nov 20 2023 at 16:27):Getting the environment variables or or time actually ends up not hitting this due to needing to await a task. So it would be something like
Task.await Time.now \time -> ...
seems like the reason that function is a task is because of this
Brendan Hansknecht (Nov 20 2023 at 16:29):I don't follow exactly what you mean.
noonien (Nov 20 2023 at 16:30):I don't see any reason for Time.now to return a task on most platforms.
noonien (Nov 20 2023 at 16:30):nor why it would receive a callback
Brendan Hansknecht (Nov 20 2023 at 16:31):Oh, it has to in roc. There is no other option. It is not a pure function. Every I/o primitive in roc has to be wrapped in the effect API.
noonien (Nov 20 2023 at 16:31):i see, and the effect API only works with tasks?
noonien (Nov 20 2023 at 16:31):can the platform not supply no-argument functions to roc?
Brendan Hansknecht (Nov 20 2023 at 16:32):Task is built on top of the effect API. It is just used everywhere for convenience of being able to handle errors.
Brendan Hansknecht (Nov 20 2023 at 16:33):can the platform not supply no-argument functions to roc?
Time.now would be an example of an effect that takes no arguments. Stdout.line would be an example of the reverse. 1 input with no result.
noonien (Nov 20 2023 at 16:35):ah, i see, i read that code wrong, the function was not an argument to Time.now, but to task.await
Brendan Hansknecht (Nov 20 2023 at 16:36):Yes, sorry about the confusion.
noonien (Nov 20 2023 at 16:36):but, how does Task.await call a function with no arguments?
Brendan Hansknecht (Nov 20 2023 at 16:38):Effects aren't technically functions. They are more like futures. So Time.now would actually just be a constant. Eventually, this code will get to builtin effect stuff that the compiler implements internally to connect the platform to the application. I forget the exact function that is call, but it is similar to await and takes an effect and a callback.
Brendan Hansknecht (Nov 20 2023 at 16:39):This will then call a roc_fx_TimeNow function that the platform exposes to roc and do what is necessary to wrap that up as an effect.
noonien (Nov 20 2023 at 16:40):i see
noonien (Nov 20 2023 at 16:42):hmm, are Tags functions? or can they just be called as functions?
Brendan Hansknecht (Nov 20 2023 at 16:44):A tag name is also a function for generating that tag variant.
Brendan Hansknecht (Nov 20 2023 at 16:46):Enable you to something like |> List.map Ok which should wrap all of the elements in a list with the Ok tag.
noonien (Nov 20 2023 at 16:47):i'm guessing |> List.map None would not work, requiring |> List.map \_ -> None instead
Brendan Hansknecht (Nov 20 2023 at 16:50):Correct, if you had a None variant that takes no args, I think it only gets a constant of the variant rather than a function cause there would be no valid way to generate it with a function.
noonien (Nov 20 2023 at 16:51):the convention is that every identifier that starts with an uppercase letter is a tag, right?
Brendan Hansknecht (Nov 20 2023 at 16:54):Uppercase is a Type in general. So you might see
Result ok err : [Ok ok, Err err]
But you would also see uppercase for a tuple or record:
Tup : (Str, U8)
Person : { height: U32, name: Str }
Oh, I guess uppercase is also used for module names as in List.map
noonien (Nov 20 2023 at 16:57):i was a bit confused about this in the repl
» foo = \n -> "hello \(n)"
: Str -> Str
» foo
: Str -> Str
» Bool
Bool : [Bool]
» Bool.true
Bool.true : Bool
you can refer to identifiers with lowercase first letter, but not with uppercase, because they are turned into tags
Brendan Hansknecht (Nov 20 2023 at 16:59):Yes, all value identifiers are required to start with lower case letters in roc.
noonien (Nov 20 2023 at 16:59):except type identifiers
noonien (Nov 20 2023 at 16:59):and module identifiers
Brendan Hansknecht (Nov 20 2023 at 17:00):So, roc will automatically infer types. If you just type an uppercase name into code somewhere, it has to be a variant of a tag.
Brendan Hansknecht (Nov 20 2023 at 17:00):That is what happens when you just type a capital word into the repl.
noonien (Nov 20 2023 at 17:00):yup
noonien (Nov 20 2023 at 17:01):is there a way to find the definition of a type?
noonien (Nov 20 2023 at 17:02):say you define the following type:
Tup : (Str, U8)
Is it possible to find out what a Tup is, in the repl?
Brendan Hansknecht (Nov 20 2023 at 17:02):Hmm... I don't think so
noonien (Nov 20 2023 at 17:03):fair enough
Brendan Hansknecht (Nov 20 2023 at 17:03):Good feature idea though
Brendan Hansknecht (Nov 20 2023 at 17:04):May be hard given we are a fully compiled language and not an interpreter though.
noonien (Nov 20 2023 at 17:05):I'm actually working on a simple language myself, and I'm trying to understand how roc works and what tradeoffs have been made. simplicity always comes at a cost, but the cost can most of the time not be an issue
noonien (Nov 20 2023 at 17:05):Brendan Hansknecht said:
May be hard given we are a fully compiled language and not an interpreter though.
yes, this would only be a repl feature
Jacob (Nov 20 2023 at 17:05):Yeah this is one thing I miss from lean. Using #eval or #check in the editor and seeing live results in the editor is amazing.
Last updated: Jul 26 2025 at 12:14 UTC