Stream: contributing

Topic: tuples on roc-for-elm-programmers

dank (Mar 26 2023 at 07:24):

https://github.com/roc-lang/roc/blob/main/roc-for-elm-programmers.md#standard-library
i went through this just to see if i missed something that wasn't in the tutorial i should know about

the part about tuples seemed outdated so thought i'd quickly update it
but then i had a look, https://github.com/roc-lang/roc/tree/main/crates/compiler/builtins
i see tuple is not implemented like the rest of the builtins
i found a decoding module of it but not sure how it's actually implemented

so it's partly the case that roc does have tuples, but does not expose a Tuple module
how does that work?

Ayaz Hafiz (Mar 26 2023 at 14:05):

Yeah, tuples are a builtin type, but there is no module devoted to providing utilities for tuples

Ayaz Hafiz (Mar 26 2023 at 14:05):

just like records/tags are types, but have no dedicated builtin module

dank (Mar 26 2023 at 14:43):

oh right
hm where is the compiler logic for them?
i would've thought there's more to it than just the decoding part

dank (Mar 26 2023 at 14:46):

like how am i able to index into it?

Folkert de Vries (Mar 26 2023 at 15:09):

pattern match?

Brendan Hansknecht (Mar 26 2023 at 15:53):

@dank , There are a lot of references to tuples directly in the IR. That is how we get both destucturing (a, b) = someTuple and direct access someTuple.0.

A few examples:

• expr for defining a tuple
• expr for accessing a specific field in a tuple
• pattern for tuple destructuring

dank (Mar 26 2023 at 15:56):

Folkert de Vries said:

pattern match?

no i meant direct access like what brendan mentioned

dank (Mar 26 2023 at 15:56):

Brendan Hansknecht said:

dank , There are a lot of references to tuples directly in the IR. That is how we get both destucturing (a, b) = someTuple and direct access someTuple.0.

A few examples:

• expr for defining a tuple
• expr for accessing a specific field in a tuple
• pattern for tuple destructuring

thanks!!

Richard Feldman (Mar 26 2023 at 17:38):

yeah the idea is that, like records and tag unions, we shouldn't need a module because there's enough built-in syntax that you don't really need it

Richard Feldman (Mar 26 2023 at 17:38):

so instead of needing like a Tuple.snd or something, you can just have .1

dank (Mar 27 2023 at 09:17):

btw so why did you guys decide not to offer mapping functions over tuples?

Ron Panduwana (Mar 27 2023 at 09:21):

because elements in a tuple can have different data types?

dank (Mar 27 2023 at 09:22):

no I mean like Elm's mapFirst/Second/Both

Richard Feldman (Mar 27 2023 at 13:46):

just doesn't seem worth a whole module, to be honest

Richard Feldman (Mar 27 2023 at 13:46):

especially considering you have to implement a separate one for each arity of tuple, which means you have to decide where to draw the line on what arity to support

Richard Feldman (Mar 27 2023 at 13:46):

we could always add syntax sugar for it if it seemed worth it

Georges Boris (Mar 30 2023 at 09:12):

so tuples ended up not being extensible? (I remember the reasoning was to enable tuple functions that weren't coupled to the tuple arity)

Ayaz Hafiz (Mar 30 2023 at 12:50):

They are extensible- you can define a “fst” function that unpacks the first element of any size tuple

Last updated: Jul 26 2025 at 12:14 UTC