diff --git a/TODO.TXT b/TODO.TXT
index b21f012..98d9bc6 100644
--- a/TODO.TXT
+++ b/TODO.TXT
@@ -1,5 +1,8 @@
 X parser
-  error handling (compiler message)
+X error handling (compiler message)
+  user-defined type resolving
+  make enum for generic types
+  location for each declarations
   expression resolving
   enum support
   union support
diff --git a/biner.l b/biner.l
index a149e97..904979b 100644
--- a/biner.l
+++ b/biner.l
@@ -1,7 +1,6 @@
 %option noinput nounput noyywrap
 
 %{
-
 #include <assert.h>
 #include <errno.h>
 #include <inttypes.h>
@@ -11,10 +10,34 @@
 
 #include "generated/biner.y.h"
 
-#define ctx (biner_tree_parse_context_)
+static inline biner_zone_ptr(char) strnew_(void);
+static inline intmax_t parse_int_(int base);
+static inline void count_(void);
+%}
 
-static inline uintptr_t strnew_(const char* str) {
-  return biner_zone_strnew(&ctx.zone, str);
+D [0-9]
+I [A-Za-z_]
+H [0-9A-Fa-f]
+
+%%
+
+"//".* count_();
+[/][*][^*]*[*]+([^*/][^*]*[*]+)*[/] count_(); /* TODO: detect unterminated comment */
+
+"struct" { count_(); return STRUCT; }
+
+{I}({I}|{D})* { yylval.ptr = strnew_(); count_(); return IDENT; }
+
+{D}+      { yylval.i = parse_int_(10); count_(); return INTEGER; }
+0[xX]{H}+ { yylval.i = parse_int_(16); count_(); return INTEGER; }
+
+[\+\-\*\/\.\(\)[\]\{\}\;] { count_(); return yytext[0]; }
+
+(.|\n) count_();
+
+%%
+static inline uintptr_t strnew_(void) {
+  return biner_zone_strnew(&biner_tree_parse_context_.zone, yytext);
 }
 static inline intmax_t parse_int_(int base) {
   char*          end = NULL;
@@ -27,26 +50,15 @@ static inline intmax_t parse_int_(int base) {
 
   return v;
 }
-%}
-
-D [0-9]
-I [A-Za-z_]
-H [0-9A-Fa-f]
-
-%%
-
-"//".* ;
-[/][*][^*]*[*]+([^*/][^*]*[*]+)*[/] ; /* TODO: detect unterminated comment */
-
-"struct" return STRUCT;
-
-{I}({I}|{D})* { yylval.ptr = strnew_(yytext); return IDENT; }
-
-{D}+      { yylval.i = parse_int_(10); return INTEGER; }
-0[xX]{H}+ { yylval.i = parse_int_(16); return INTEGER; }
-
-[\+\-\*\/\.\(\)[\]\{\}\;] return yytext[0];
-
-(.|\n) ;
-
-%%
+static inline void count_(void) {
+  const char* s = yytext;
+  while (*s) {
+    if (*s == '\n') {
+      biner_tree_parse_context_.column = 0;
+      ++biner_tree_parse_context_.line;
+    } else {
+      ++biner_tree_parse_context_.column;
+    }
+    ++s;
+  }
+}
diff --git a/biner.y b/biner.y
index 473cabd..29d1428 100644
--- a/biner.y
+++ b/biner.y
@@ -11,26 +11,34 @@
 
 #define ctx (biner_tree_parse_context_)
 
-#define alloc_(T)  (biner_zone_alloc(&ctx.zone, sizeof(T)))
+#define alloc_(T) (biner_zone_alloc(&ctx.zone, sizeof(T)))
 #define ref(T, p) ((T*) (ctx.zone.ptr+p))
 
-extern int  yylex(void);
-extern void yyerror(const char*);
+extern char* yytext;
+
+extern int yylex(void);
+
+#define yyerrorf(fmt, ...)  \
+  fprintf(stderr, "[%zu:%zu] "fmt"\n", ctx.line+1, ctx.column+1, __VA_ARGS__)
+#define yyerror(msg)  \
+  fprintf(stderr, "[%zu:%zu] "msg"\n", ctx.line+1, ctx.column+1)
+
+static inline biner_zone_ptr(biner_tree_decl_t) find_decl_by_name_(
+  biner_zone_ptr(char) name);
 
 static inline biner_zone_ptr(biner_tree_struct_member_t)
-find_struct_member_(
-    biner_zone_ptr(biner_tree_struct_member_t) itr,
-    biner_zone_ptr(char)                       name) {
-  while (itr) {
-    const biner_tree_struct_member_t* m = ref(biner_tree_struct_member_t, itr);
-    if (strcmp(ref(char, m->name), ref(char, name)) == 0) {
-      return itr;
-    }
-    itr = m->prev;
-  }
-  yyerror("unknown member");
-  return 0;
-}
+find_struct_member_by_name_(
+  biner_zone_ptr(biner_tree_struct_member_t) last_member,
+  biner_zone_ptr(char)                       name);
+
+static inline biner_zone_ptr(biner_tree_struct_member_t)
+find_child_struct_member_by_name_(
+    biner_zone_ptr(biner_tree_struct_member_t) member,
+    biner_zone_ptr(char)                       name);
+
+static inline biner_zone_ptr(biner_tree_struct_member_t)
+unwrap_struct_member_ref_(
+    biner_zone_ptr(biner_tree_struct_member_reference_t) memref);
 %}
 
 %union {
@@ -66,6 +74,10 @@ decl_list
 
 decl
   : STRUCT IDENT '{' struct_body '}' ';' {
+    if (find_decl_by_name_($2) != 0) {
+      yyerrorf("duplicated declaration of '%s'", ref(char, $2));
+      YYABORT;
+    }
     $$ = alloc_(biner_tree_decl_t);
     *ref(biner_tree_decl_t, $$) = (biner_tree_decl_t) {
       .name   = $2,
@@ -88,6 +100,10 @@ struct_body
 
 struct_member
   : struct_member_type IDENT ';' {
+    if (find_struct_member_by_name_(ctx.last_member, $2) != 0) {
+      yyerrorf("duplicated struct member of '%s'", ref(char, $2));
+      YYABORT;
+    }
     $$ = alloc_(biner_tree_struct_member_t);
     *ref(biner_tree_struct_member_t, $$) =
       (biner_tree_struct_member_t) {
@@ -113,7 +129,7 @@ struct_member_type
     *ref(biner_tree_struct_member_type_t, $$) =
       (biner_tree_struct_member_type_t) {
         .kind      = BINER_TREE_STRUCT_MEMBER_TYPE_KIND_GENERIC,
-        .generic      = $1,
+        .generic   = $1,
         .qualifier = BINER_TREE_STRUCT_MEMBER_TYPE_QUALIFIER_DYNAMIC_ARRAY,
         .expr      = $3,
       };
@@ -180,34 +196,82 @@ operand
 
 struct_member_reference
   : IDENT {
+    const biner_zone_ptr(biner_tree_struct_member_t) member =
+      find_struct_member_by_name_(ctx.last_member, $1);
+    if (member == 0) {
+      yyerrorf("unknown member '%s'", ref(char, $1));
+      YYABORT;
+    }
+
     $$ = alloc_(biner_tree_struct_member_reference_t);
     *ref(biner_tree_struct_member_reference_t, $$) =
-      (biner_tree_struct_member_reference_t) {
-        .member = find_struct_member_(ctx.last_member, $1),
-      };
+      (biner_tree_struct_member_reference_t) { .member = member, };
   }
   | struct_member_reference '.' IDENT {
-    const biner_tree_struct_member_t* p =
-      ref(biner_tree_struct_member_t, $1);
-
-    const biner_tree_struct_member_type_t* t =
-      ref(biner_tree_struct_member_type_t, p->type);
-    if (t->kind != BINER_TREE_STRUCT_MEMBER_TYPE_KIND_USER_DEFINED) {
-      yyerror("not user-defined data");
+    const biner_zone_ptr(biner_tree_struct_member_t) member =
+      find_child_struct_member_by_name_(unwrap_struct_member_ref_($1), $3);
+    if (member == 0) {
+      yyerrorf("unknown member '%s'", ref(char, $3));
       YYABORT;
     }
 
-    const biner_tree_decl_t* d = ref(biner_tree_decl_t, t->decl);
-    if (d->type != BINER_TREE_DECL_TYPE_STRUCT) {
-      yyerror("not struct");
-      YYABORT;
-    }
     $$ = alloc_(biner_tree_struct_member_reference_t);
     *ref(biner_tree_struct_member_reference_t, $$) =
-      (biner_tree_struct_member_reference_t) {
-        .member = find_struct_member_(d->member, $3),
-      };
+      (biner_tree_struct_member_reference_t) { .member = member, };
   }
   ;
 
 %%
+static inline biner_zone_ptr(biner_tree_decl_t) find_decl_by_name_(
+    biner_zone_ptr(char) name) {
+  biner_zone_ptr(biner_tree_decl_t) itr = ctx.last_decl;
+  while (itr) {
+    const biner_tree_decl_t* decl = ref(biner_tree_decl_t, itr);
+    if (strcmp(ref(char, decl->name), ref(char, name)) == 0) return itr;
+    itr = decl->prev;
+  }
+  return 0;
+}
+
+static inline biner_zone_ptr(biner_tree_struct_member_t)
+find_struct_member_by_name_(
+    biner_zone_ptr(biner_tree_struct_member_t) last_member,
+    biner_zone_ptr(char)                       name) {
+  biner_zone_ptr(biner_tree_struct_member_t) itr = last_member;
+  while (itr) {
+    const biner_tree_struct_member_t* m = ref(biner_tree_struct_member_t, itr);
+    if (strcmp(ref(char, m->name), ref(char, name)) == 0) return itr;
+    itr = m->prev;
+  }
+  return 0;
+}
+
+static inline biner_zone_ptr(biner_tree_struct_member_t)
+find_child_struct_member_by_name_(
+    biner_zone_ptr(biner_tree_struct_member_t) member,
+    biner_zone_ptr(char)                       name) {
+  const biner_tree_struct_member_t* m = ref(biner_tree_struct_member_t, member);
+
+  const biner_tree_struct_member_type_t* t =
+    ref(biner_tree_struct_member_type_t, m->type);
+  if (t->kind != BINER_TREE_STRUCT_MEMBER_TYPE_KIND_USER_DEFINED) {
+    yyerrorf("typeof '%s' is not user-defined", ref(char, m->name));
+    return 0;
+  }
+  const biner_tree_decl_t* d = ref(biner_tree_decl_t, t->decl);
+  if (d->type != BINER_TREE_DECL_TYPE_STRUCT) {
+    yyerrorf("'%s' (typeof '%s') is not struct",
+      ref(char, d->name),
+      ref(char, m->name));
+    return 0;
+  }
+  return find_struct_member_by_name_(d->member, name);
+}
+
+static inline biner_zone_ptr(biner_tree_struct_member_t)
+unwrap_struct_member_ref_(
+    biner_zone_ptr(biner_tree_struct_member_reference_t) memref) {
+  const biner_tree_struct_member_reference_t* r =
+    ref(biner_tree_struct_member_reference_t, memref);
+  return r->member;
+}
diff --git a/tree.c b/tree.c
index ac5c848..a4ab2cf 100644
--- a/tree.c
+++ b/tree.c
@@ -14,12 +14,6 @@
 
 biner_tree_parse_context_t biner_tree_parse_context_ = {0};
 
-int yyerror(char* str) {
-  extern char* yytext;
-  fprintf(stderr, "error: %s: %s\n", str, yytext);
-  return 0;
-}
-
 const uint8_t* biner_tree_parse(FILE* fp) {
   if (atomic_flag_test_and_set(&biner_tree_parse_context_.dirty)) {
     fprintf(stderr, "parsing context is dirty now\n");
diff --git a/tree.h b/tree.h
index 2ffea9c..03051d5 100644
--- a/tree.h
+++ b/tree.h
@@ -94,6 +94,9 @@ typedef struct biner_tree_parse_context_t {
   atomic_flag  dirty;
   biner_zone_t zone;
 
+  size_t line;
+  size_t column;
+
   biner_zone_ptr(biner_tree_root_t)          root;
   biner_zone_ptr(biner_tree_decl_t)          last_decl;
   biner_zone_ptr(biner_tree_struct_member_t) last_member;