diff --git a/TODO.TXT b/TODO.TXT
index 7910ced..dfb0ada 100644
--- a/TODO.TXT
+++ b/TODO.TXT
@@ -4,7 +4,7 @@ X user-defined type resolving
 X make enum for generic types
 X constant resolving in expression
 X check if an expression is static/dynamic
-  enum support
+X enum support
   constant support
   conditional switching support
   union support
diff --git a/biner.l b/biner.l
index 904979b..b60e6b3 100644
--- a/biner.l
+++ b/biner.l
@@ -24,6 +24,7 @@ H [0-9A-Fa-f]
 "//".* count_();
 [/][*][^*]*[*]+([^*/][^*]*[*]+)*[/] count_(); /* TODO: detect unterminated comment */
 
+"enum"   { count_(); return ENUM; }
 "struct" { count_(); return STRUCT; }
 
 {I}({I}|{D})* { yylval.ptr = strnew_(); count_(); return IDENT; }
@@ -31,7 +32,7 @@ H [0-9A-Fa-f]
 {D}+      { yylval.i = parse_int_(10); count_(); return INTEGER; }
 0[xX]{H}+ { yylval.i = parse_int_(16); count_(); return INTEGER; }
 
-[\+\-\*\/\.\(\)[\]\{\}\;] { count_(); return yytext[0]; }
+[\+\-\*\/\=\.\(\)[\]\{\}\;\,] { count_(); return yytext[0]; }
 
 (.|\n) count_();
 
diff --git a/biner.y b/biner.y
index 76dcecd..84a43b7 100644
--- a/biner.y
+++ b/biner.y
@@ -24,10 +24,11 @@ extern int yylex(void);
 #define yyerror(msg)  \
   fprintf(stderr, "[%zu:%zu] "msg"\n", ctx.line+1, ctx.column+1)
 
-static inline bool
-unstringify_struct_member_type_name_(
-  biner_tree_struct_member_type_name_t* name,
-  biner_zone_ptr(char)                  str
+static inline biner_zone_ptr(biner_tree_decl_t)
+create_decl_(
+  biner_zone_ptr(char)   name,
+  biner_tree_decl_type_t type,
+  biner_zone_ptr(void)   body
 );
 
 static inline biner_zone_ptr(biner_tree_decl_t)
@@ -35,9 +36,21 @@ find_decl_by_name_(
   biner_zone_ptr(char) name
 );
 
+static inline biner_zone_ptr(biner_tree_expr_t)
+find_enum_member_by_name_(
+  biner_zone_ptr(biner_tree_enum_member_t) tail_member,
+  biner_zone_ptr(char)                     name
+);
+
+static inline bool
+unstringify_struct_member_type_name_(
+  biner_tree_struct_member_type_name_t* name,
+  biner_zone_ptr(char)                  str
+);
+
 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(biner_tree_struct_member_t) tail_member,
   biner_zone_ptr(char)                       name
 );
 
@@ -70,11 +83,12 @@ resolve_constant_(
   uintptr_t ptr;
 }
 
-%token STRUCT
+%token ENUM STRUCT
 %token <ptr> IDENT
 %token <i>   INTEGER;
 
 %type <ptr> decl_list decl
+%type <ptr> enum_member_list enum_member
 %type <ptr> struct_member_list struct_member
 %type <ptr> struct_member_type array_struct_member_type unqualified_struct_member_type
 %type <ptr> expr add_expr mul_expr operand
@@ -98,34 +112,65 @@ decl_list
   ;
 
 decl
-  : STRUCT IDENT '{' struct_member_list '}' ';' {
-    if (find_decl_by_name_($2) != 0) {
-      yyerrorf("duplicated declaration of '%s'", ref(char, $2));
+  : ENUM IDENT '{' enum_member_list '}' ';' {
+    $$ = create_decl_($2, BINER_TREE_DECL_TYPE_ENUM, $4);
+    if ($$ == 0) YYABORT;
+  }
+  | ENUM IDENT '{' enum_member_list ',' '}' ';' {
+    $$ = create_decl_($2, BINER_TREE_DECL_TYPE_ENUM, $4);
+    if ($$ == 0) YYABORT;
+  }
+  | STRUCT IDENT '{' struct_member_list '}' ';' {
+    $$ = create_decl_($2, BINER_TREE_DECL_TYPE_STRUCT, $4);
+    if ($$ == 0) YYABORT;
+  }
+  ;
+
+enum_member_list
+  : enum_member {
+    $$ = ctx.last_enum = $1;
+  }
+  | enum_member_list ',' enum_member {
+    ref(biner_tree_enum_member_t, $3)->prev = $1;
+    $$ = ctx.last_enum = $3;
+  }
+  ;
+
+enum_member
+  : IDENT '=' expr {
+    if (resolve_constant_($1) != 0) {
+      yyerrorf("duplicated symbol name, '%s'", ref(char, $1));
       YYABORT;
     }
-    $$ = alloc_(biner_tree_decl_t);
-    *ref(biner_tree_decl_t, $$) = (biner_tree_decl_t) {
-      .name   = $2,
-      .member = $4,
+    if (ref(biner_tree_expr_t, $3)->dynamic) {
+      yyerrorf("dynamic expression is not allowed for enum member, '%s'", ref(char, $1));
+      YYABORT;
+    }
+    $$ = alloc_(biner_tree_enum_member_t);
+    *ref(biner_tree_enum_member_t, $$) = (biner_tree_enum_member_t) {
+      .name = $1,
+      .expr = $3,
     };
-    ctx.last_decl   = $$;
-    ctx.last_member = 0;
   }
   ;
 
 struct_member_list
   : struct_member {
-    $$ = ctx.last_member = $1;
+    $$ = ctx.last_struct = $1;
   }
   | struct_member_list struct_member {
     ref(biner_tree_struct_member_t, $2)->prev = $1;
-    $$ = ctx.last_member = $2;
+    $$ = ctx.last_struct = $2;
   }
   ;
 
 struct_member
   : struct_member_type IDENT ';' {
-    if (find_struct_member_by_name_(ctx.last_member, $2) != 0) {
+    if (resolve_constant_($2) != 0) {
+      yyerrorf("duplicated symbol name, '%s'", ref(char, $2));
+      YYABORT;
+    }
+    if (find_struct_member_by_name_(ctx.last_struct, $2) != 0) {
       yyerrorf("duplicated struct member of '%s'", ref(char, $2));
       YYABORT;
     }
@@ -213,7 +258,7 @@ operand
   }
   | IDENT {
     const biner_zone_ptr(biner_tree_struct_member_t) m =
-      find_struct_member_by_name_(ctx.last_member, $1);
+      find_struct_member_by_name_(ctx.last_struct, $1);
     if (m != 0) {
       biner_zone_ptr(biner_tree_struct_member_reference_t) mref =
         alloc_(biner_tree_struct_member_reference_t);
@@ -261,17 +306,27 @@ operand
   ;
 
 %%
-static inline bool unstringify_struct_member_type_name_(
-    biner_tree_struct_member_type_name_t* name,
-    biner_zone_ptr(char)                  str) {
-  for (size_t i = 0; i < BINER_TREE_STRUCT_MEMBER_TYPE_NAME_MAX_; ++i) {
-    const char* item = biner_tree_struct_member_type_name_string_map[i];
-    if (item != NULL && strcmp(ref(char, str), item) == 0) {
-      *name = (biner_tree_struct_member_type_name_t) i;
-      return true;
-    }
+static inline biner_zone_ptr(biner_tree_decl_t) create_decl_(
+    biner_zone_ptr(char)   name,
+    biner_tree_decl_type_t type,
+    biner_zone_ptr(void)   body) {
+  if (resolve_constant_(name) != 0) {
+    yyerrorf("duplicated symbol name, '%s'", ref(char, name));
+    return 0;
   }
-  return false;
+  if (find_decl_by_name_(name) != 0) {
+    yyerrorf("duplicated declaration of '%s'", ref(char, name));
+    return 0;
+  }
+  biner_zone_ptr(biner_tree_decl_t) decl = alloc_(biner_tree_decl_t);
+  *ref(biner_tree_decl_t, decl) = (biner_tree_decl_t) {
+    .name = name,
+    .type = type,
+    .body = body,
+  };
+  ctx.last_decl = decl;
+  ctx.last_body = 0;
+  return decl;
 }
 
 static inline biner_zone_ptr(biner_tree_decl_t) find_decl_by_name_(
@@ -285,11 +340,38 @@ static inline biner_zone_ptr(biner_tree_decl_t) find_decl_by_name_(
   return 0;
 }
 
+static inline biner_zone_ptr(biner_tree_expr_t) find_enum_member_by_name_(
+  biner_zone_ptr(biner_tree_enum_member_t) tail_member,
+  biner_zone_ptr(char)                     name) {
+  biner_zone_ptr(biner_tree_enum_member_t) itr = tail_member;
+  while (itr) {
+    const biner_tree_enum_member_t* member = ref(biner_tree_enum_member_t, itr);
+    if (strcmp(ref(char, member->name), ref(char, name)) == 0) {
+      return member->expr;
+    }
+    itr = member->prev;
+  }
+  return 0;
+}
+
+static inline bool unstringify_struct_member_type_name_(
+    biner_tree_struct_member_type_name_t* name,
+    biner_zone_ptr(char)                  str) {
+  for (size_t i = 0; i < BINER_TREE_STRUCT_MEMBER_TYPE_NAME_MAX_; ++i) {
+    const char* item = biner_tree_struct_member_type_name_string_map[i];
+    if (item != NULL && strcmp(ref(char, str), item) == 0) {
+      *name = (biner_tree_struct_member_type_name_t) i;
+      return true;
+    }
+  }
+  return false;
+}
+
 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(biner_tree_struct_member_t) tail_member,
     biner_zone_ptr(char)                       name) {
-  biner_zone_ptr(biner_tree_struct_member_t) itr = last_member;
+  biner_zone_ptr(biner_tree_struct_member_t) itr = tail_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;
@@ -317,7 +399,7 @@ find_child_struct_member_by_name_(
       ref(char, m->name));
     return 0;
   }
-  return find_struct_member_by_name_(d->member, name);
+  return find_struct_member_by_name_(d->struct_, name);
 }
 
 static inline biner_zone_ptr(biner_tree_struct_member_t)
@@ -346,7 +428,22 @@ static inline biner_zone_ptr(biner_tree_expr_t) create_operator_(
 
 static inline biner_zone_ptr(biner_tree_expr_t) resolve_constant_(
     biner_zone_ptr(char) ident) {
-  (void) ident;
-  /* TODO: find out enums and constants */
+  biner_zone_ptr(biner_tree_expr_t) expr =
+    find_enum_member_by_name_(ctx.last_enum, ident);
+  if (expr != 0) return expr;
+
+  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);
+    switch (decl->type) {
+    case BINER_TREE_DECL_TYPE_ENUM:
+      expr = find_enum_member_by_name_(decl->enum_, ident);
+      break;
+    default:
+      ;
+    }
+    if (expr != 0) return expr;
+    itr = decl->prev;
+  }
   return 0;
 }
diff --git a/main.c b/main.c
index cca323c..8094573 100644
--- a/main.c
+++ b/main.c
@@ -1,9 +1,49 @@
+#include <assert.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 
 #include "./tree.h"
 
+static inline void print_enum_(
+    const uint8_t* zone, const biner_tree_decl_t* decl) {
+  assert(zone != NULL);
+  assert(decl != NULL);
+
+  printf("enum %s:\n", zone + decl->name);
+  const biner_tree_enum_member_t* member =
+    (const biner_tree_enum_member_t*) (zone + decl->enum_);
+  while ((uintptr_t) member != (uintptr_t) zone) {
+    printf("  %s\n", zone + member->name);
+    member = (const biner_tree_enum_member_t*) (zone + member->prev);
+  }
+}
+
+static inline void print_struct_(
+    const uint8_t* zone, const biner_tree_decl_t* decl) {
+  assert(zone != NULL);
+  assert(decl != NULL);
+
+  printf("struct %s:\n", zone + decl->name);
+  const biner_tree_struct_member_t* member =
+    (const biner_tree_struct_member_t*) (zone + decl->struct_);
+  while ((uintptr_t) member != (uintptr_t) zone) {
+    printf("  ");
+    const biner_tree_struct_member_type_t* type =
+      (const biner_tree_struct_member_type_t*) (zone + member->type);
+    if (type->name == BINER_TREE_STRUCT_MEMBER_TYPE_NAME_USER_DECL) {
+      const biner_tree_decl_t* decl =
+        (const biner_tree_decl_t*) (zone + type->decl);
+      printf("%8s ", zone + decl->name);
+    } else {
+      printf("%8s ",
+        biner_tree_struct_member_type_name_string_map[type->name]);
+    }
+    printf("%s\n", zone + member->name);
+    member = (const biner_tree_struct_member_t*) (zone + member->prev);
+  }
+}
+
 int main(void) {
   const uint8_t* zone = biner_tree_parse(stdin);
   if (zone == NULL) return EXIT_FAILURE;
@@ -13,24 +53,15 @@ int main(void) {
   const biner_tree_decl_t* decl =
     (const biner_tree_decl_t*) (zone + root->decls);
   while ((uintptr_t) decl != (uintptr_t) zone) {
-    printf("%s:\n", zone + decl->name);
-
-    const biner_tree_struct_member_t* member =
-      (const biner_tree_struct_member_t*) (zone + decl->member);
-    while ((uintptr_t) member != (uintptr_t) zone) {
-      printf("  ");
-      const biner_tree_struct_member_type_t* type =
-        (const biner_tree_struct_member_type_t*) (zone + member->type);
-      if (type->name == BINER_TREE_STRUCT_MEMBER_TYPE_NAME_USER_DECL) {
-        const biner_tree_decl_t* decl =
-          (const biner_tree_decl_t*) (zone + type->decl);
-        printf("%8s ", zone + decl->name);
-      } else {
-        printf("%8s ",
-          biner_tree_struct_member_type_name_string_map[type->name]);
-      }
-      printf("%s\n", zone + member->name);
-      member = (const biner_tree_struct_member_t*) (zone + member->prev);
+    switch (decl->type) {
+    case BINER_TREE_DECL_TYPE_ENUM:
+      print_enum_(zone, decl);
+      break;
+    case BINER_TREE_DECL_TYPE_STRUCT:
+      print_struct_(zone, decl);
+      break;
+    default:
+      ;
     }
     decl = (const biner_tree_decl_t*) (zone + decl->prev);
   }
diff --git a/tree.h b/tree.h
index 8d523db..092b1d7 100644
--- a/tree.h
+++ b/tree.h
@@ -13,7 +13,7 @@
 typedef struct biner_tree_expr_t                    biner_tree_expr_t;
 typedef struct biner_tree_struct_member_t           biner_tree_struct_member_t;
 typedef struct biner_tree_struct_member_reference_t biner_tree_struct_member_reference_t;
-typedef struct biner_tree_struct_t                  biner_tree_struct_t;
+typedef struct biner_tree_enum_member_t             biner_tree_enum_member_t;
 typedef struct biner_tree_decl_t                    biner_tree_decl_t;
 
 typedef enum biner_tree_expr_type_t {
@@ -78,7 +78,6 @@ typedef struct biner_tree_struct_member_type_t {
 
 typedef struct biner_tree_struct_member_t {
   biner_zone_ptr(char)                            name;
-  biner_zone_ptr(biner_tree_struct_t)             owner;
   biner_zone_ptr(biner_tree_struct_member_type_t) type;
 
   biner_zone_ptr(biner_tree_struct_member_t) prev;
@@ -90,15 +89,25 @@ typedef struct biner_tree_struct_member_reference_t {
   biner_zone_ptr(biner_tree_struct_member_reference_t) prev;
 } biner_tree_struct_member_reference_t;
 
+typedef struct biner_tree_enum_member_t {
+  biner_zone_ptr(char)                     name;
+  biner_zone_ptr(biner_tree_expr_t)        expr;
+  biner_zone_ptr(biner_tree_enum_member_t) prev;
+} biner_tree_enum_member_t;
+
 typedef enum biner_tree_decl_type_t {
   BINER_TREE_DECL_TYPE_STRUCT,
+  BINER_TREE_DECL_TYPE_ENUM,
 } biner_tree_decl_type_t;
 
 typedef struct biner_tree_decl_t {
   biner_zone_ptr(char) name;
   biner_tree_decl_type_t type;
   union {
-    biner_zone_ptr(biner_tree_struct_member_t) member;
+    biner_zone_ptr(void) body;
+
+    biner_zone_ptr(biner_tree_struct_member_t) struct_;
+    biner_zone_ptr(biner_tree_enum_member_t)   enum_;
   };
   biner_zone_ptr(biner_tree_decl_t) prev;
 } biner_tree_decl_t;
@@ -114,9 +123,15 @@ typedef struct biner_tree_parse_context_t {
   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;
+  biner_zone_ptr(biner_tree_root_t) root;
+  biner_zone_ptr(biner_tree_decl_t) last_decl;
+
+  union {
+    biner_zone_ptr(void) last_body;
+
+    biner_zone_ptr(biner_tree_struct_member_t) last_struct;
+    biner_zone_ptr(biner_tree_enum_member_t)   last_enum;
+  };
 } biner_tree_parse_context_t;
 
 extern biner_tree_parse_context_t biner_tree_parse_context_;