Different return types causing error

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Hi!

I hope it is okay to post ReScript help requests here, but please direct me to a more appropriate place if this forum is just about ReScript roadmap etc.

I’m coming from the JS/TS world and I cannot for the life of me figure out how to have a function that can return different types. Here’s a playground link: https://reasonml.github.io/en/try?rrjsx=false&reason=C4TwDgpgBAbhBOAjA9gZwgeQK7DDqAvFAN4BQUsAhgDYCWAJgFxQrLUA05UAthKqpQDmEZqmDxaAO0GcAvgG5SpahGBQIAD0rcwKwlwoAKAH4BjABYRTAawTsox4OamCAKsgDClm-eMwaDACyfALCvlL+dPTB-EIQvpQAQshszKzUAJSEAHwkXCpqtKgAagH0hFAWVrbwhk4u7l7VGYpcSSnUUAD8BiSRDMxFpVH2vLHCgyVl3VRRMaHQg5L90SFxslCMvUNligqkQA

I would very much appreciate some help.

Thanks,

Will.

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AFAIK it’s ok to ask questions in this forum.

Unlike js/ts/flow in ReScript/Reason your function can just return a single type,
in such cases like you mentiond above, you have to use a variant.

I have updated your example using a variant.
Variant is powerful feature of rescript’s type system, read more about them on rescript docs.
Feel free to ask questions

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Thanks! And thanks for the updated playground; it’s really useful to have these examples to work from.

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I would add to this, that you will probably be interested in an @unboxed type, as that combines the best of both worlds. Type safety at compile time but no additional cost at runtime.

See this article for reference
https://reasonml.org/blog/union-types-in-bucklescript

Patrick has also written an interesting article on the topic:


And last but certainly not least, there is the @bs.inline option as described by Yawar Amin here:
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