feat(library/head_map): a simple indexing datastructure

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/library/CMakeLists.txt

@@ -6,7 +6,7 @@ add_library(library deep_copy.cpp expr_lt.cpp io_state.cpp occurs.cpp
   update_declaration.cpp choice.cpp scoped_ext.cpp locals.cpp
   standard_kernel.cpp hott_kernel.cpp
   unifier.cpp unifier_plugin.cpp inductive_unifier_plugin.cpp
-  explicit.cpp num.cpp string.cpp opaque_hints.cpp)
+  explicit.cpp num.cpp string.cpp opaque_hints.cpp head_map.cpp)
 # hop_match.cpp)
 
 target_link_libraries(library ${LEAN_LIBS})

src/library/head_map.cpp

@@ -0,0 +1,23 @@
+/*
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#include "library/head_map.h"
+
+namespace lean {
+head_index::head_index(expr const & e) {
+    expr const & f = get_app_fn(e);
+    m_kind = f.kind();
+    if (is_constant(f))
+        m_const_name = const_name(f);
+}
+
+int head_index::cmp::operator()(head_index const & i1, head_index const & i2) const {
+    if (i1.m_kind != i2.m_kind || i1.m_kind != expr_kind::Constant)
+        return static_cast<int>(i1.m_kind) - static_cast<int>(i2.m_kind);
+    else
+        return quick_cmp(i1.m_const_name, i2.m_const_name);
+}
+}

src/library/head_map.h

@@ -0,0 +1,64 @@
+/*
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#pragma once
+#include "util/rb_map.h"
+#include "util/list.h"
+#include "kernel/expr.h"
+
+namespace lean {
+struct head_index {
+    expr_kind m_kind;
+    name      m_const_name;
+    explicit head_index(expr_kind k = expr_kind::Var):m_kind(k) {}
+    explicit head_index(name const & c):m_kind(expr_kind::Constant), m_const_name(c) {}
+    head_index(expr const & e);
+
+    struct cmp {
+        int operator()(head_index const & i1, head_index const & i2) const;
+    };
+};
+
+/**
+    \brief Very simple indexing data-structure that allow us to map the head symbol of an expression to
+    a list of values.
+
+    The index is the expression kind and a name (if it is a constant).
+
+    This index is very naive, but it is effective for many applications.
+*/
+template<typename V>
+class head_map {
+    rb_map<head_index, list<V>, head_index::cmp> m_map;
+public:
+    bool empty() const { return m_map.empty(); }
+    bool contains(head_index const & h) const { return m_map.contains(h); }
+    list<V> const * find(head_index const & h) const { return m_map.find(h); }
+    void erase(head_index const & h) { m_map.erase(h); }
+    void erase_entry(head_index const & h, V const & v) {
+        if (auto it = m_map.find(h)) {
+            auto new_vs = filter(*it, [&](V const & v2) { return v != v2; });
+            if (!new_vs)
+                m_map.erase(h);
+            else
+                m_map.insert(h, new_vs);
+        }
+    }
+    void insert(head_index const & h, V const & v) {
+        if (auto it = m_map.find(h))
+            m_map.insert(h, cons(v, filter(*it, [&](V const & v2) { return v != v2; })));
+        else
+            m_map.insert(h, list<V>(v));
+    }
+    template<typename F> void for_each(F && f) const { m_map.for_each(f); }
+    template<typename F> void for_each_entry(F && f) const {
+        m_map.for_each([&](head_index const & h, list<V> const & vs) {
+                for (V const & v : vs)
+                    f(h, v);
+            });
+    }
+};
+}

src/tests/library/CMakeLists.txt

@@ -10,3 +10,6 @@ add_test(occurs ${CMAKE_CURRENT_BINARY_DIR}/occurs)
 add_executable(unifier unifier.cpp)
 target_link_libraries(unifier ${EXTRA_LIBS})
 add_test(unifier ${CMAKE_CURRENT_BINARY_DIR}/unifier)
+add_executable(head_map head_map.cpp)
+target_link_libraries(head_map ${EXTRA_LIBS})
+add_test(head_map ${CMAKE_CURRENT_BINARY_DIR}/head_map)

src/tests/library/head_map.cpp

@@ -0,0 +1,59 @@
+/*
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#include "util/test.h"
+#include "kernel/abstract.h"
+#include "library/head_map.h"
+using namespace lean;
+
+static void tst1() {
+    head_map<expr> map;
+    expr a = Const("a");
+    expr f = Const("f");
+    expr b = Const("b");
+    expr x = Local("x", Bool);
+    expr l1 = Fun(x, x);
+    expr l2 = Fun(x, f(x));
+    lean_assert(l1 != l2);
+    lean_assert(map.empty());
+    map.insert(a, a);
+    lean_assert(map.contains(a));
+    map.insert(a, b);
+    lean_assert(map.contains(a));
+    map.erase_entry(a, b);
+    lean_assert(map.contains(a));
+    map.erase_entry(a, a);
+    lean_assert(!map.contains(a));
+    lean_assert(map.empty());
+    map.insert(l1, a);
+    map.insert(l2, b);
+    lean_assert(map.contains(l1));
+    lean_assert(length(*map.find(l1)) == 2);
+    auto size_fn = [](head_map<expr> const & m) {
+        unsigned r = 0;
+        m.for_each_entry([&](head_index const &, expr const &) { r++; });
+        return r;
+    };
+    lean_assert(size_fn(map) == 2);
+    map.insert(a, a);
+    lean_assert(size_fn(map) == 3);
+    map.erase(l1);
+    lean_assert(size_fn(map) == 1);
+    map.insert(a, b);
+    lean_assert(size_fn(map) == 2);
+    map.erase(a);
+    lean_assert(size_fn(map) == 0);
+    lean_assert(map.empty());
+    map.insert(f(a), f(a));
+    map.insert(f(b), f(b));
+    lean_assert(length(*map.find(f(a))) == 2);
+}
+
+int main() {
+    save_stack_info();
+    tst1();
+    return has_violations() ? 1 : 0;
+}