38 lines
1.2 KiB
Text
38 lines
1.2 KiB
Text
/-
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Copyright (c) 2016 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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Author: Leonardo de Moura
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-/
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prelude
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import init.char init.list
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definition string [reducible] := list char
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namespace string
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definition empty : string := list.nil
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definition str : char → string → string := list.cons
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definition concat (a b : string) : string :=
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list.append b a
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end string
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definition string.has_append [instance] : has_append string :=
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has_append.mk string.concat
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open list
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private definition utf8_length_aux : nat → nat → string → nat
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| 0 r (c::s) :=
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let n := char.to_nat c in
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if n < 0x80 then utf8_length_aux 0 (r+1) s
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else if 0xC0 ≤ n ∧ n < 0xE0 then utf8_length_aux 1 (r+1) s
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else if 0xE0 ≤ n ∧ n < 0xF0 then utf8_length_aux 2 (r+1) s
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else if 0xF0 ≤ n ∧ n < 0xF8 then utf8_length_aux 3 (r+1) s
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else if 0xF8 ≤ n ∧ n < 0xFC then utf8_length_aux 4 (r+1) s
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else if 0xFC ≤ n ∧ n < 0xFE then utf8_length_aux 5 (r+1) s
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else utf8_length_aux 0 (r+1) s
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| (n+1) r (c::s) := utf8_length_aux n r s
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| _ r [] := r
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definition utf8_length : string → nat
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| s := utf8_length_aux 0 0 (reverse s)
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