008b7b2ac2
In Lean4, the check should be based on the compiler. That is, a definition should be marked as noncomputable when we cannot generate code for it.
11 lines
510 B
Text
11 lines
510 B
Text
def ℝ := set ℕ
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constant ℝ.sub' : ℝ → ℝ → ℝ
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/-
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The following definition is accepted because the type is (ℝ → ℝ → ℝ) which is defeq to (ℝ → ℝ → ℕ → Prop).
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The code generator can handle it because it is returning a type. Morally, it is the function that takes
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three arguments and returns an unit.
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-/
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def ℝ.sub (a b : ℝ) := (λ b, a.sub' b) b
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instance : has_sub ℝ := ⟨ℝ.sub⟩
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constant ℝ.nonneg : ℝ → Prop
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instance : has_le ℝ := ⟨λ a b, (b - a).nonneg⟩
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