13 lines
295 B
Markdown
13 lines
295 B
Markdown
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## Recall: System F
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```agda
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ℕ : Set₁
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ℕ = ∀ {A} → (A → A) → A → A
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zero : ℕ
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zero = λ f x → x
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suc : ℕ → ℕ
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suc = λ n f x → f (n f x)
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fold : ∀ {A} → (A → A) → A → ℕ → A
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fold = λ f x n → n f x
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-- add : ℕ → ℕ → ℕ
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-- add = λ n → fold suc n
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```
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