29 lines
743 B
C++
29 lines
743 B
C++
/*
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Copyright (c) 2013 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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#include <utility>
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#include "util/exception.h"
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#include "kernel/context.h"
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namespace lean {
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std::pair<name, expr> const & lookup(context const & c, unsigned i) {
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auto const * it = &c;
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while (*it) {
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if (i == 0)
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return head(*it);
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--i;
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it = &tail(*it);
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}
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throw exception("unknown free variable");
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}
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optional<std::pair<name, expr>> find(context const & c, unsigned i) {
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try {
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return optional<std::pair<name, expr>>(lookup(c, i));
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} catch (exception &) {
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return optional<std::pair<name, expr>>();
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}
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}
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}
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