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chore: upstream Char lemmas from Mathlib #4348

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Jun 5, 2024
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chore: upstream Char lemmas from Mathlib #4348

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9 changes: 8 additions & 1 deletion src/Init/Data/Char/Basic.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ theorem isValidUInt32 (n : Nat) (h : isValidCharNat n) : n < UInt32.size := by
apply Nat.lt_trans h₂
decide

theorem isValidChar_of_isValidChar_Nat (n : Nat) (h : isValidCharNat n) : isValidChar (UInt32.ofNat' n (isValidUInt32 n h)) :=
theorem isValidChar_of_isValidCharNat (n : Nat) (h : isValidCharNat n) : isValidChar (UInt32.ofNat' n (isValidUInt32 n h)) :=
match h with
| Or.inl h => Or.inl h
| Or.inr ⟨h₁, h₂⟩ => Or.inr ⟨h₁, h₂⟩
Expand All @@ -52,6 +52,13 @@ theorem isValidChar_zero : isValidChar 0 :=
@[inline] def toNat (c : Char) : Nat :=
c.val.toNat

/-- Convert a character into a `UInt8`, by truncating (reducing modulo 256) if necessary. -/
@[inline] def toUInt8 (c : Char) : UInt8 :=
c.val.toUInt8

/-- The numbers from 0 to 256 are all valid UTF-8 characters, so we can embed one in the other. -/
def ofUInt8 (n : UInt8) : Char := ⟨n.toUInt32, .inl (Nat.lt_trans n.1.2 (by decide))⟩

instance : Inhabited Char where
default := 'A'

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9 changes: 9 additions & 0 deletions src/Init/Data/Char/Lemmas.lean
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Expand Up @@ -22,4 +22,13 @@ protected theorem le_total (a b : Char) : a ≤ b ∨ b ≤ a := UInt32.le_total
protected theorem lt_asymm {a b : Char} (h : a < b) : ¬ b < a := UInt32.lt_asymm h
protected theorem ne_of_lt {a b : Char} (h : a < b) : a ≠ b := Char.ne_of_val_ne (UInt32.ne_of_lt h)

theorem utf8Size_pos (c : Char) : 0 < c.utf8Size := by
simp only [utf8Size]
repeat (split; decide)
decide

@[simp] theorem ofNat_toNat (c : Char) : Char.ofNat c.toNat = c := by
rw [Char.ofNat, dif_pos]
rfl

end Char
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