diff --git a/src/compile.h b/src/compile.h
index f2578c9..76c7322 100644
--- a/src/compile.h
+++ b/src/compile.h
@@ -52,3 +52,8 @@ static void str_dtor(zval *zv)
 {
     zend_string_release_ex(Z_STR_P(zv), 0);
 }
+
+static zend_string *zend_concat_names(char *name1, size_t name1_len, char *name2, size_t name2_len)
+{
+    return zend_string_concat3(name1, name1_len, "\\", 1, name2, name2_len);
+}
diff --git a/src/extension.c b/src/extension.c
index 844f64e..093dda1 100644
--- a/src/extension.c
+++ b/src/extension.c
@@ -69,6 +69,11 @@ static PHP_MINIT_FUNCTION(vyrtue)
 
     // Register constants
     REGISTER_STRING_CONSTANT("VyrtueExt\\VERSION", (char *) PHP_VYRTUE_VERSION, flags);
+#ifdef VYRTUE_DEBUG
+    REGISTER_BOOL_CONSTANT("VyrtueExt\\DEBUG", true, flags);
+#else
+    REGISTER_BOOL_CONSTANT("VyrtueExt\\DEBUG", false, flags);
+#endif
 
     if (NULL == original_ast_process) {
         original_ast_process = zend_ast_process;
diff --git a/src/preprocess.c b/src/preprocess.c
index ca6fbd9..bfb5e65 100644
--- a/src/preprocess.c
+++ b/src/preprocess.c
@@ -28,28 +28,30 @@
 #include "Zend/zend_exceptions.h"
 #include "main/php.h"
 #include "main/php_streams.h"
-#include "ext/standard/php_string.h"
 #include "php_vyrtue.h"
 #include "compile.h"
 
 struct vyrtue_preprocess_context
 {
-    bool should_perform_second_pass;
+    bool in_namespace;
     zend_string *current_namespace;
     HashTable *imports;
     HashTable *imports_function;
     HashTable *imports_const;
+    HashTable *seen_symbols;
 };
 
+static zend_ast *vyrtue_ast_walk(zend_ast *ast, struct vyrtue_preprocess_context *ctx);
+
 /**
  * @see zend_get_import_ht
  * @license Zend-2.0
  */
-static HashTable *vyrtue_get_import_ht(uint32_t type, struct vyrtue_preprocess_context *ctx) /* {{{ */
+static HashTable *vyrtue_get_import_ht(uint32_t type, struct vyrtue_preprocess_context *ctx)
 {
     switch (type) {
         case ZEND_SYMBOL_CLASS:
-            if (ctx->imports) {
+            if (!ctx->imports) {
                 ctx->imports = emalloc(sizeof(HashTable));
                 zend_hash_init(ctx->imports, 8, NULL, str_dtor, 0);
             }
@@ -96,24 +98,84 @@ static void vyrtue_reset_import_tables(struct vyrtue_preprocess_context *ctx)
     }
 }
 
+static void vyrtue_end_namespace(struct vyrtue_preprocess_context *ctx)
+{
+    ctx->in_namespace = false;
+    vyrtue_reset_import_tables(ctx);
+    if (ctx->current_namespace) {
+#ifdef VYRTUE_DEBUG
+        if (UNEXPECTED(NULL != getenv("PHP_VYRTUE_DEBUG_DUMP_NAMESPACE"))) {
+            fprintf(
+                stderr, "VYRTUE_NAMESPACE: LEFT: %.*s\n", (int) ctx->current_namespace->len, ctx->current_namespace->val
+            );
+        }
+#endif
+        ctx->current_namespace = NULL;
+    }
+}
+
+static void vyrtue_register_seen_symbol(zend_string *name, uint32_t kind, struct vyrtue_preprocess_context *ctx)
+{
+    zval *zv = zend_hash_find(ctx->seen_symbols, name);
+    if (zv) {
+        Z_LVAL_P(zv) |= kind;
+    } else {
+        zval tmp;
+        ZVAL_LONG(&tmp, kind);
+        zend_hash_add_new(ctx->seen_symbols, name, &tmp);
+    }
+}
+
+static bool vyrtue_have_seen_symbol(zend_string *name, uint32_t kind, struct vyrtue_preprocess_context *ctx)
+{
+    zval *zv = zend_hash_find(ctx->seen_symbols, name);
+    return zv && (Z_LVAL_P(zv) & kind) != 0;
+}
+
 /**
  * @see zend_compile_namespace
  */
-static void vyrtue_ast_first_pass_namespace(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
+static void vyrtue_ast_process_namespace(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
 {
     zend_ast *name_ast = ast->child[0];
+    zend_ast *stmt_ast = ast->child[1];
+    bool with_bracket = stmt_ast != NULL;
+
+    // there is a bunch of validation here in zend_compile_namespace that we *might* not need
 
     if (name_ast) {
         ctx->current_namespace = zend_ast_get_str(name_ast);
     } else {
         ctx->current_namespace = NULL;
     }
+
+    vyrtue_reset_import_tables(ctx);
+
+    ctx->in_namespace = true;
+
+    if (with_bracket) {
+        // FC(has_bracketed_namespaces) = 1;
+    }
+
+#ifdef VYRTUE_DEBUG
+    if (UNEXPECTED(NULL != getenv("PHP_VYRTUE_DEBUG_DUMP_NAMESPACE"))) {
+        fprintf(
+            stderr, "VYRTUE_NAMESPACE: ENTER: %.*s\n", (int) ctx->current_namespace->len, ctx->current_namespace->val
+        );
+    }
+#endif
+
+    if (stmt_ast) {
+        zend_ast *replace_child = vyrtue_ast_walk(stmt_ast, ctx);
+        ZEND_ASSERT(replace_child == NULL);
+        vyrtue_end_namespace(ctx);
+    }
 }
 
 /**
  * @see zend_compile_use
  */
-static void vyrtue_ast_first_pass_use(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
+static void vyrtue_ast_process_use(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
 {
     zend_ast_list *list = zend_ast_get_list(ast);
     uint32_t i;
@@ -152,33 +214,68 @@ static void vyrtue_ast_first_pass_use(zend_ast *ast, struct vyrtue_preprocess_co
             zend_str_tolower_copy(ZSTR_VAL(ns_name), ZSTR_VAL(current_ns), ZSTR_LEN(current_ns));
             ZSTR_VAL(ns_name)[ZSTR_LEN(current_ns)] = '\\';
             memcpy(ZSTR_VAL(ns_name) + ZSTR_LEN(current_ns) + 1, ZSTR_VAL(lookup_name), ZSTR_LEN(lookup_name) + 1);
-
-            //            if (zend_have_seen_symbol(ns_name, type)) {
-            //                zend_check_already_in_use(type, old_name, new_name, ns_name);
-            //            }
-
             zend_string_efree(ns_name);
-        } /* else if (zend_have_seen_symbol(lookup_name, type)) {
-            zend_check_already_in_use(type, old_name, new_name, lookup_name);
-        } */
+        }
 
         zend_string_addref(old_name);
         old_name = zend_new_interned_string(old_name);
-        zend_hash_add_ptr(current_import, lookup_name, old_name);
 
-        // @todo we could potentially check for registered macros here
+        if (!zend_hash_add_ptr(current_import, lookup_name, old_name)) {
+            // symbol was imported twice - let zend_compile handle the error
+        }
+
+#ifdef VYRTUE_DEBUG
+        if (UNEXPECTED(NULL != getenv("PHP_VYRTUE_DEBUG_DUMP_USE"))) {
+            fprintf(
+                stderr,
+                "VYRTUE_USE: %.*s => %.*s\n",
+                (int) old_name->len,
+                old_name->val,
+                (int) new_name->len,
+                new_name->val
+            );
+        }
+#endif
 
         zend_string_release_ex(lookup_name, 0);
         zend_string_release_ex(new_name, 0);
     }
 }
 
-static void vyrtue_ast_first_pass(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
+/**
+ * @see zend_compile_group_use
+ */
+static void vyrtue_ast_process_group_use(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
 {
-    if (ast->kind != ZEND_AST_STMT_LIST) {
-        return;
+    uint32_t i;
+    zend_string *ns = zend_ast_get_str(ast->child[0]);
+    zend_ast_list *list = zend_ast_get_list(ast->child[1]);
+
+    for (i = 0; i < list->children; i++) {
+        zend_ast *inline_use, *use = list->child[i];
+        zval *name_zval = zend_ast_get_zval(use->child[0]);
+        zend_string *name = Z_STR_P(name_zval);
+        zend_string *compound_ns = zend_concat_names(ZSTR_VAL(ns), ZSTR_LEN(ns), ZSTR_VAL(name), ZSTR_LEN(name));
+        zend_string_release_ex(name, 0);
+        ZVAL_STR(name_zval, compound_ns);
+        inline_use = zend_ast_create_list(1, ZEND_AST_USE, use);
+        inline_use->attr = ast->attr ? ast->attr : use->attr;
+        vyrtue_ast_process_use(inline_use, ctx);
     }
+}
+
+static zend_ast *vyrtue_ast_enter_node(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
+{
+    return NULL;
+}
+
+static zend_ast *vyrtue_ast_leave_node(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
+{
+    return NULL;
+}
 
+static void vyrtue_ast_walk_list(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
+{
     zend_ast_list *list = zend_ast_get_list(ast);
 
     for (int i = 0; i < list->children; i++) {
@@ -187,42 +284,88 @@ static void vyrtue_ast_first_pass(zend_ast *ast, struct vyrtue_preprocess_contex
             continue;
         }
 
-        //        fprintf(stderr, "|%d %d %d| \n", (int) child->kind, ZEND_AST_NAMESPACE, ZEND_AST_USE);
+        zend_ast *replace_child = vyrtue_ast_walk(child, ctx);
 
-        switch (child->kind) {
-            case ZEND_AST_NAMESPACE:
-                vyrtue_ast_first_pass_namespace(child, ctx);
-                break;
-            case ZEND_AST_USE:
-                vyrtue_ast_first_pass_use(child, ctx);
-                break;
+        if (UNEXPECTED(replace_child != NULL)) {
+            zend_ast_destroy(list->child[i]);
+            list->child[i] = replace_child;
         }
     }
 }
 
-static void vyrtue_ast_second_pass(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
+static void vyrtue_ast_walk_children(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
 {
-    // todo
+    uint32_t i, children = zend_ast_get_num_children(ast);
+    for (i = 0; i < children; i++) {
+        if (UNEXPECTED(ast->child[i] == NULL)) {
+            continue;
+        }
+
+        zend_ast *replace_child = vyrtue_ast_walk(ast->child[i], ctx);
+
+        if (UNEXPECTED(replace_child != NULL)) {
+            zend_ast_destroy(ast->child[i]);
+            ast->child[i] = replace_child;
+        }
+    }
 }
 
-VYRTUE_PUBLIC void vyrtue_ast_process_file(zend_ast *ast)
+static zend_ast *vyrtue_ast_walk(zend_ast *ast, struct vyrtue_preprocess_context *ctx)
 {
-    struct vyrtue_preprocess_context ctx = {
-        .should_perform_second_pass = false,
-    };
+    zend_ast *replace_child;
 
-    vyrtue_ast_first_pass(ast, &ctx);
+    if (NULL == ast) {
+        return NULL;
+    }
+
+    // these have special handling
+    switch (ast->kind) {
+        case ZEND_AST_NAMESPACE:
+            vyrtue_ast_process_namespace(ast, ctx);
+            return NULL;
+
+        case ZEND_AST_USE:
+            vyrtue_ast_process_use(ast, ctx);
+            return NULL;
+
+        case ZEND_AST_GROUP_USE:
+            vyrtue_ast_process_group_use(ast, ctx);
+            return NULL;
+    }
+
+    replace_child = vyrtue_ast_enter_node(ast, ctx);
+    if (replace_child) {
+        // @TODO should we recurse on the replacement (also, below for leave node)?
+        return replace_child;
+    }
 
-    if (ctx.should_perform_second_pass) {
-        vyrtue_ast_second_pass(ast, &ctx);
+    if (zend_ast_is_list(ast)) {
+        vyrtue_ast_walk_list(ast, ctx);
+    } else {
+        vyrtue_ast_walk_children(ast, ctx);
     }
 
+    return vyrtue_ast_leave_node(ast, ctx);
+}
+
+VYRTUE_PUBLIC void vyrtue_ast_process_file(zend_ast *ast)
+{
+    struct vyrtue_preprocess_context ctx = {0};
+
+    ctx.seen_symbols = emalloc(sizeof(HashTable));
+    zend_hash_init(ctx.seen_symbols, 8, NULL, NULL, 0);
+
+    zend_ast *replace_child = vyrtue_ast_walk(ast, &ctx);
+    ZEND_ASSERT(replace_child == NULL);
+
 #ifdef VYRTUE_DEBUG
-    if (NULL != getenv("PHP_VYRTUE_DEBUG_DUMP")) {
+    if (UNEXPECTED(NULL != getenv("PHP_VYRTUE_DEBUG_DUMP_AST"))) {
         zend_string *str = zend_ast_export("<?php\n", ast, "");
-        fprintf(stderr, "%.*s", str->len, str->val);
+        fprintf(stderr, "%.*s", (int) str->len, str->val);
+        zend_string_release(str);
     }
 #endif
 
-    vyrtue_reset_import_tables(&ctx);
+    vyrtue_end_namespace(&ctx);
+    zend_hash_destroy(ctx.seen_symbols);
 }
diff --git a/tests/namespace/detection-01.phpt b/tests/namespace/detection-01.phpt
new file mode 100644
index 0000000..3f38764
--- /dev/null
+++ b/tests/namespace/detection-01.phpt
@@ -0,0 +1,19 @@
+--TEST--
+namespace detection 01
+--EXTENSIONS--
+vyrtue
+--ENV--
+PHP_VYRTUE_DEBUG_DUMP_NAMESPACE=1
+PHP_VYRTUE_DEBUG_DUMP_USE=1
+--SKIPIF--
+<?php if (!VyrtueExt\DEBUG) die("Skipped: vyrtue not debug build"); ?>
+--FILE--
+<?php
+namespace FooBar;
+use function Foo\bar;
+use function Foo\bat as booyah;
+--EXPECT--
+VYRTUE_NAMESPACE: ENTER: FooBar
+VYRTUE_USE: Foo\bar => bar
+VYRTUE_USE: Foo\bat => booyah
+VYRTUE_NAMESPACE: LEFT: FooBar
diff --git a/tests/namespace/detection-02.phpt b/tests/namespace/detection-02.phpt
new file mode 100644
index 0000000..e632b25
--- /dev/null
+++ b/tests/namespace/detection-02.phpt
@@ -0,0 +1,38 @@
+--TEST--
+namespace detection 02
+--EXTENSIONS--
+vyrtue
+--ENV--
+PHP_VYRTUE_DEBUG_DUMP_NAMESPACE=1
+PHP_VYRTUE_DEBUG_DUMP_USE=1
+--SKIPIF--
+<?php if (!VyrtueExt\DEBUG) die("Skipped: vyrtue not debug build"); ?>
+--FILE--
+<?php
+// from https://www.php.net/manual/en/language.namespaces.importing.php
+namespace foo;
+use My\Full\Classname as Another;
+
+// this is the same as use My\Full\NSname as NSname
+use My\Full\NSname;
+
+// importing a global class
+use ArrayObject;
+
+// importing a function
+use function My\Full\functionName;
+
+// aliasing a function
+use function My\Full\functionName as func;
+
+// importing a constant
+use const My\Full\CONSTANT;
+--EXPECT--
+VYRTUE_NAMESPACE: ENTER: foo
+VYRTUE_USE: My\Full\Classname => Another
+VYRTUE_USE: My\Full\NSname => NSname
+VYRTUE_USE: ArrayObject => ArrayObject
+VYRTUE_USE: My\Full\functionName => functionName
+VYRTUE_USE: My\Full\functionName => func
+VYRTUE_USE: My\Full\CONSTANT => CONSTANT
+VYRTUE_NAMESPACE: LEFT: foo
diff --git a/tests/namespace/detection-03.phpt b/tests/namespace/detection-03.phpt
new file mode 100644
index 0000000..150fe9b
--- /dev/null
+++ b/tests/namespace/detection-03.phpt
@@ -0,0 +1,36 @@
+--TEST--
+namespace detection 03
+--EXTENSIONS--
+vyrtue
+--ENV--
+PHP_VYRTUE_DEBUG_DUMP_NAMESPACE=1
+PHP_VYRTUE_DEBUG_DUMP_USE=1
+--SKIPIF--
+<?php if (!VyrtueExt\DEBUG) die("Skipped: vyrtue not debug build"); ?>
+--FILE--
+<?php
+namespace FooBar {
+    use My\Full\Classname as Another;
+    use My\Full\NSname;
+    use function My\Full\functionName;
+    use function My\Full\functionName as func;
+}
+namespace BarBat {
+    use My\Full\Classname as Another;
+    use My\Full\NSname;
+    use function My\Full\functionName;
+    use function My\Full\functionName as func;
+}
+--EXPECT--
+VYRTUE_NAMESPACE: ENTER: FooBar
+VYRTUE_USE: My\Full\Classname => Another
+VYRTUE_USE: My\Full\NSname => NSname
+VYRTUE_USE: My\Full\functionName => functionName
+VYRTUE_USE: My\Full\functionName => func
+VYRTUE_NAMESPACE: LEFT: FooBar
+VYRTUE_NAMESPACE: ENTER: BarBat
+VYRTUE_USE: My\Full\Classname => Another
+VYRTUE_USE: My\Full\NSname => NSname
+VYRTUE_USE: My\Full\functionName => functionName
+VYRTUE_USE: My\Full\functionName => func
+VYRTUE_NAMESPACE: LEFT: BarBat
diff --git a/tests/namespace/detection-04.phpt b/tests/namespace/detection-04.phpt
new file mode 100644
index 0000000..2ebc102
--- /dev/null
+++ b/tests/namespace/detection-04.phpt
@@ -0,0 +1,15 @@
+--TEST--
+namespace detection 04
+--EXTENSIONS--
+vyrtue
+--ENV--
+PHP_VYRTUE_DEBUG_DUMP_NAMESPACE=1
+PHP_VYRTUE_DEBUG_DUMP_USE=1
+--SKIPIF--
+<?php if (!VyrtueExt\DEBUG) die("Skipped: vyrtue not debug build"); ?>
+--FILE--
+<?php
+use My\Full\Classname as Another, My\Full\NSname;
+--EXPECT--
+VYRTUE_USE: My\Full\Classname => Another
+VYRTUE_USE: My\Full\NSname => NSname
diff --git a/tests/namespace/detection-05.phpt b/tests/namespace/detection-05.phpt
new file mode 100644
index 0000000..800c46b
--- /dev/null
+++ b/tests/namespace/detection-05.phpt
@@ -0,0 +1,24 @@
+--TEST--
+namespace detection 05
+--EXTENSIONS--
+vyrtue
+--ENV--
+PHP_VYRTUE_DEBUG_DUMP_NAMESPACE=1
+PHP_VYRTUE_DEBUG_DUMP_USE=1
+--SKIPIF--
+<?php if (!VyrtueExt\DEBUG) die("Skipped: vyrtue not debug build"); ?>
+--FILE--
+<?php
+use some\namespace\{ClassA, ClassB, ClassC as C};
+use function some\namespace\{fn_a, fn_b, fn_c};
+use const some\namespace\{ConstA, ConstB, ConstC};
+--EXPECT--
+VYRTUE_USE: some\namespace\ClassA => ClassA
+VYRTUE_USE: some\namespace\ClassB => ClassB
+VYRTUE_USE: some\namespace\ClassC => C
+VYRTUE_USE: some\namespace\fn_a => fn_a
+VYRTUE_USE: some\namespace\fn_b => fn_b
+VYRTUE_USE: some\namespace\fn_c => fn_c
+VYRTUE_USE: some\namespace\ConstA => ConstA
+VYRTUE_USE: some\namespace\ConstB => ConstB
+VYRTUE_USE: some\namespace\ConstC => ConstC