84 lines
2.2 KiB
Text
84 lines
2.2 KiB
Text
/-
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Copyright (c) 2014 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Module: init.num
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Authors: Leonardo de Moura
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-/
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prelude
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import init.logic init.bool
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open bool
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definition pos_num.is_inhabited [instance] : inhabited pos_num :=
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inhabited.mk pos_num.one
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namespace pos_num
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definition is_one (a : pos_num) : bool :=
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pos_num.rec_on a tt (λn r, ff) (λn r, ff)
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definition pred (a : pos_num) : pos_num :=
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pos_num.rec_on a one (λn r, bit0 n) (λn r, cond (is_one n) one (bit1 r))
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definition size (a : pos_num) : pos_num :=
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pos_num.rec_on a one (λn r, succ r) (λn r, succ r)
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definition add (a b : pos_num) : pos_num :=
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pos_num.rec_on a
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succ
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(λn f b, pos_num.rec_on b
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(succ (bit1 n))
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(λm r, succ (bit1 (f m)))
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(λm r, bit1 (f m)))
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(λn f b, pos_num.rec_on b
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(bit1 n)
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(λm r, bit1 (f m))
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(λm r, bit0 (f m)))
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b
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notation a + b := add a b
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definition mul (a b : pos_num) : pos_num :=
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pos_num.rec_on a
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b
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(λn r, bit0 r + b)
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(λn r, bit0 r)
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notation a * b := mul a b
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end pos_num
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definition num.is_inhabited [instance] : inhabited num :=
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inhabited.mk num.zero
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namespace num
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open pos_num
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definition pred (a : num) : num :=
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num.rec_on a zero (λp, cond (is_one p) zero (pos (pred p)))
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definition size (a : num) : num :=
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num.rec_on a (pos one) (λp, pos (size p))
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definition add (a b : num) : num :=
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num.rec_on a b (λp_a, num.rec_on b (pos p_a) (λp_b, pos (pos_num.add p_a p_b)))
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definition mul (a b : num) : num :=
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num.rec_on a zero (λp_a, num.rec_on b zero (λp_b, pos (pos_num.mul p_a p_b)))
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notation a + b := add a b
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notation a * b := mul a b
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end num
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-- the coercion from num to nat is defined here, so that it can already be used in init.trunc
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namespace nat
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definition add (a b : nat) : nat :=
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nat.rec_on b a (λ b₁ r, succ r)
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notation a + b := add a b
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definition of_num [coercion] (n : num) : nat :=
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num.rec zero
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(λ n, pos_num.rec (succ zero) (λ n r, r + r + (succ zero)) (λ n r, r + r) n) n
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end nat
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attribute nat.of_num [reducible] -- of_num is also reducible if namespace "nat" is not opened
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