feat(library): add simple normalization procedure

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

src/library/CMakeLists.txt

@@ -1,6 +1,6 @@
 add_library(library deep_copy.cpp expr_lt.cpp io_state.cpp occurs.cpp
   kernel_bindings.cpp io_state_stream.cpp bin_app.cpp
-  resolve_macro.cpp kernel_serializer.cpp max_sharing.cpp)
+  resolve_macro.cpp kernel_serializer.cpp max_sharing.cpp normalize.cpp)
 # placeholder.cpp fo_unify.cpp hop_match.cpp)
 
 target_link_libraries(library ${LEAN_LIBS})

src/library/normalize.cpp

@@ -0,0 +1,48 @@
+/*
+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/name_generator.h"
+#include "kernel/type_checker.h"
+#include "kernel/instantiate.h"
+#include "kernel/abstract.h"
+
+namespace lean {
+static name g_tmp_prefix = name::mk_internal_unique_name();
+
+class normalize_fn {
+    type_checker   m_tc;
+    name_generator m_ngen;
+
+    expr normalize_binding(expr const & e) {
+        expr d = normalize(binding_domain(e));
+        expr l = mk_local(m_ngen.next(), binding_name(e), d);
+        expr b = abstract(normalize(instantiate(binding_body(e), l)), l);
+        return update_binding(e, d, b);
+    }
+
+    expr normalize(expr e) {
+        e = m_tc.whnf(e);
+        switch (e.kind()) {
+        case expr_kind::Var:  case expr_kind::Constant: case expr_kind::Sort:
+        case expr_kind::Meta: case expr_kind::Local: case expr_kind::Macro:
+            return e;
+        case expr_kind::Let:
+            lean_unreachable(); // LCOV_EXCL_LINE
+        case expr_kind::Lambda: case expr_kind::Pi:
+            return normalize_binding(e);
+        case expr_kind::App:
+            return update_app(e, app_fn(e), normalize(app_arg(e)));
+        }
+        lean_unreachable(); // LCOV_EXCL_LINE
+    }
+
+public:
+    normalize_fn(environment const & env):m_tc(env), m_ngen(g_tmp_prefix) {}
+    expr operator()(expr const & e) { return normalize(e); }
+};
+
+expr normalize(environment const & env, expr const & e) { return normalize_fn(env)(e); }
+}

src/library/normalize.h

@@ -0,0 +1,13 @@
+/*
+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 "kernel/expr.h"
+
+namespace lean {
+/** \brief Return the \c e normal form with respect to the environment \c env. */
+expr normalize(environment const & env, expr const & e);
+}