9338aabed9
This PR changes the interface of the `ForIn`, `ForIn'`, and `ForM` typeclasses to not take a `Monad m` parameter. This is a breaking change for most downstream `instance`s, which will will now need to assume `[Monad m]`. The rationale is that if the provider of an instance requires `m` to be a Monad, they should assume this up front. This makes it possible for the instanve to assume `LawfulMonad m` or some other stronger requirement, and also to provided a concrete instance for a particular `m` without assuming a non-canonical `Monad` structure on it. Zulip: [#lean4 > Monad assumptions in fields of other typeclasses @ 💬](https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/Monad.20assumptions.20in.20fields.20of.20other.20typeclasses/near/537102158)
79 lines
1.6 KiB
Text
79 lines
1.6 KiB
Text
set_option pp.mvars.anonymous false
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/--
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error: failed to construct 'ForIn' instance for collection
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?_
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and monad
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Id
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-/
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#guard_msgs in
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example {c} := Id.run do
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for x in c do
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pure ()
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pure ()
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/--
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error: don't know how to synthesize implicit argument `ρ`
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@forIn Id (List ?_) ?_ instForInOfForIn' PUnit [] PUnit.unit fun x r => do
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pure ()
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pure (ForInStep.yield PUnit.unit)
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context:
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⊢ Type _
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---
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error: Failed to infer type of binder `x`
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---
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error: don't know how to synthesize implicit argument `α`
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@List.nil ?_
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context:
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⊢ Type _
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-/
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#guard_msgs in
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example : Unit := Id.run do
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for x in [] do
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pure ()
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pure ()
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/--
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error: failed to construct `ForIn'` instance for collection
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?_
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and monad
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Id
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-/
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#guard_msgs in
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example {c} := Id.run do
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for h : x in c do
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pure ()
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pure ()
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/--
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error: don't know how to synthesize implicit argument `d`
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@forIn' Id (List ?_) ?_ inferInstance List.instForIn'InferInstanceMembershipOfMonad PUnit [] PUnit.unit fun x h r =>
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do
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pure ()
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pure (ForInStep.yield PUnit.unit)
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context:
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⊢ outParam (Membership ?_ (List ?_))
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---
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error: don't know how to synthesize implicit argument `ρ`
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@forIn' Id (List ?_) ?_ inferInstance List.instForIn'InferInstanceMembershipOfMonad PUnit [] PUnit.unit fun x h r =>
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do
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pure ()
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pure (ForInStep.yield PUnit.unit)
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context:
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⊢ Type _
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---
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error: Failed to infer type of binder `h`
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---
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error: Failed to infer type of binder `x`
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---
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error: don't know how to synthesize implicit argument `α`
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@List.nil ?_
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context:
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⊢ Type _
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-/
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#guard_msgs in
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example : Unit := Id.run do
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for h : x in [] do
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pure ()
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pure ()
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