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feat(library/init/meta/format): has_to_format α implies has_to_string α #231

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feat(library/init/meta/format): has_to_format α implies has_to_string α #231

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6 changes: 5 additions & 1 deletion library/init/meta/format.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -53,14 +53,18 @@ meta instance : has_append format :=
⟨format.compose⟩

meta instance : has_to_string format :=
⟨λ f, f.to_string options.mk⟩
⟨λ f, f.to_string⟩

/-- Use this instead of `has_to_string` to enable prettier formatting.
See docstring for `format` for more on the differences between `format` and `string`.
Note that `format` is `meta` while `string` is not. -/
meta class has_to_format (α : Type u) :=
(to_format : α → format)

@[priority 10] meta instance has_to_format_has_to_string {α} [has_to_format α]
: has_to_string α :=
⟨has_to_string.to_string ∘ has_to_format.to_format⟩

meta instance : has_to_format format :=
⟨id⟩

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