diff --git a/examples/hello_world.l b/examples/hello_world.l
index ec4071b..8bdb256 100644
--- a/examples/hello_world.l
+++ b/examples/hello_world.l
@@ -1,10 +1,11 @@
 struct b {
-	u32 ciao,
-	u32 test,
-	u32 test1,
+	i32 a,
+	u32 b,
+	u32 c,
 }
 
-u32 test(b hello)
+u32 test()
 {
-
+	u32 a = (u32)3;
+	a = (u32)2;
 }
diff --git a/lc.c b/lc.c
index 1587486..e4a0229 100644
--- a/lc.c
+++ b/lc.c
@@ -123,12 +123,6 @@ void print_ast(ast_node *node, int depth) {
 				current = current->expr.unit_node.next;
 			}
 			break;
-		case NODE_COMPOUND: 
-			printf("Block\n");
-			for (usize i = 0; i < node->expr.compound.stmt_len; ++i) {
-				print_ast(node->expr.compound.statements[i], depth + 1);
-			}
-			break;
 		case NODE_CALL:
 			printf("Call: %.*s\n", (int)node->expr.call.name_len, node->expr.call.name);
 			current = node->expr.call.parameters;
diff --git a/lexer.c b/lexer.c
index 26c1eb1..07d1a9d 100644
--- a/lexer.c
+++ b/lexer.c
@@ -396,6 +396,8 @@ lexer *lexer_init(char *source, usize size, arena *arena)
 	lex->source = source;
 
 	keywords = arena_alloc(arena, sizeof(trie_node));
+	trie_insert(keywords, lex->allocator, "true", TOKEN_TRUE);
+	trie_insert(keywords, lex->allocator, "false", TOKEN_FALSE);
 	trie_insert(keywords, lex->allocator, "struct", TOKEN_STRUCT);
 	trie_insert(keywords, lex->allocator, "enum", TOKEN_ENUM);
 	trie_insert(keywords, lex->allocator, "union", TOKEN_UNION);
diff --git a/lexer.h b/lexer.h
index 2aa86ec..a3859ba 100644
--- a/lexer.h
+++ b/lexer.h
@@ -55,6 +55,8 @@ typedef enum {
 	TOKEN_IDENTIFIER,
 	TOKEN_STRING,
 	TOKEN_CHAR,
+	TOKEN_TRUE,
+	TOKEN_FALSE,
 	TOKEN_GOTO,
 	TOKEN_LOOP,
 	TOKEN_WHILE,
diff --git a/parser.c b/parser.c
index 3ba7c2a..96b5c87 100644
--- a/parser.c
+++ b/parser.c
@@ -428,15 +428,13 @@ ast_node *parse_expression(parser *p)
 			left = node;
 
 		}
-		return left;
 	}
 
 	/*
 	 * If after parsing an expression a `.` character
 	 * is found, it should be a member access expression.
 	 */
-	if (match_peek(p, TOKEN_DOT))
-	{
+	if (match_peek(p, TOKEN_DOT) && p->tokens->next && p->tokens->next->type != TOKEN_LCURLY) {
 		while (match(p, TOKEN_DOT)) {
 			if (!match_peek(p, TOKEN_IDENTIFIER)) {
 				error(p, "expected identifier after member access.");
@@ -450,7 +448,6 @@ ast_node *parse_expression(parser *p)
 
 			left = node;
 		}
-		return left;
 	}
 
 	/*
@@ -749,7 +746,7 @@ parse_captures:
 	arena_start = arena_snapshot(p->allocator);
 	node->expr.fr.captures = arena_alloc(p->allocator, sizeof(ast_node));
 	node->expr.fr.captures->type = NODE_UNIT;
-	node->expr.fr.captures->expr.unit_node.expr = parse_expression(p);
+	node->expr.fr.captures->expr.unit_node.expr = parse_factor(p);
 	if (node->expr.fr.captures->expr.unit_node.expr && node->expr.fr.captures->expr.unit_node.expr->type != NODE_IDENTIFIER) {
 		error(p, "captures must be identifiers.");
 		arena_reset_to_snapshot(p->allocator, arena_start);
@@ -776,7 +773,7 @@ parse_captures:
 				tail->expr.unit_node.next->expr.unit_node.expr = expr;
 				tail = tail->expr.unit_node.next;
 				tail->type = NODE_UNIT;
-				expr = parse_expression(p);
+				expr = parse_factor(p);
 				if (!expr) {
 					error(p, "expected `|`.");
 					arena_reset_to_snapshot(p->allocator, arena_start);
diff --git a/parser.h b/parser.h
index 40f9a9c..5428101 100644
--- a/parser.h
+++ b/parser.h
@@ -5,6 +5,7 @@
 #include "utils.h"
 #include <stdbool.h>
 
+struct _type;
 struct _ast_node;
 
 typedef enum {
@@ -12,21 +13,14 @@ typedef enum {
 	OP_MINUS, // -
 	OP_DIV, // /
 	OP_MUL, // *
-	OP_EQ, // ==
-	OP_ASSIGN, // =
-	OP_AND, // &&
-	OP_OR, // ||
-	OP_NEQ, // !=
-	OP_GT, // >
-	OP_LT, // <
-	OP_GE, // >=
-	OP_LE, // <=
-	OP_RSHIFT_EQ, // >>=
-	OP_LSHIFT_EQ, // <<=
+	OP_MOD, // %
 	OP_BOR, // |
 	OP_BAND, // &
 	OP_BXOR, // ^
-	OP_MOD, // %
+
+	OP_ASSIGN, // =
+	OP_RSHIFT_EQ, // >>=
+	OP_LSHIFT_EQ, // <<=
 	OP_PLUS_EQ, // +=
 	OP_MINUS_EQ, // -=
 	OP_DIV_EQ, // /=
@@ -35,6 +29,15 @@ typedef enum {
 	OP_BAND_EQ, // &=
 	OP_BXOR_EQ, // ^=
 	OP_MOD_EQ, // %=
+
+	OP_EQ, // ==
+	OP_AND, // &&
+	OP_OR, // ||
+	OP_NEQ, // !=
+	OP_GT, // >
+	OP_LT, // <
+	OP_GE, // >=
+	OP_LE, // <=
 } binary_op;
 
 typedef enum {
@@ -79,32 +82,34 @@ typedef enum {
 	NODE_FLOAT,
 	NODE_STRING,
 	NODE_CHAR,
+	NODE_BOOL,
 	NODE_CAST,
 	NODE_UNARY,
 	NODE_BINARY,
 	NODE_RANGE,
 	NODE_ARRAY_SUBSCRIPT,
-	NODE_ACCESS,
-	NODE_CALL,
 	NODE_POSTFIX,
+	NODE_CALL,
+	NODE_ACCESS,
+	NODE_STRUCT_INIT,
+	NODE_TERNARY, /* TODO */
+
 	NODE_BREAK,
 	NODE_RETURN,
-	NODE_LABEL,
-	NODE_GOTO,
 	NODE_IMPORT,
 	NODE_FOR,
 	NODE_WHILE,
 	NODE_IF,
-	NODE_COMPOUND,
+	NODE_VAR_DECL,
+	NODE_LABEL,
+	NODE_GOTO,
+
 	NODE_ENUM,
 	NODE_STRUCT,
 	NODE_UNION,
-	NODE_VAR_DECL,
 	NODE_FUNCTION,
 	NODE_PTR_TYPE,
-	NODE_TERNARY, /* TODO */
 	NODE_SWITCH, /* TODO */
-	NODE_STRUCT_INIT,
 	NODE_UNIT,
 } node_type;
 
@@ -120,6 +125,7 @@ typedef enum {
 typedef struct _ast_node {
 	node_type type;
 	source_pos position;
+	struct _type *expr_type;
 	union {
 		struct {
 			struct _ast_node *type;
@@ -138,6 +144,7 @@ typedef struct _ast_node {
 			struct _ast_node *right;
 			unary_op operator;
 		} unary;
+		u8 boolean;
 		i64 integer;
 		f64 flt; // float
 		struct {
@@ -183,9 +190,9 @@ typedef struct _ast_node {
 		struct {
 			/* These should be lists of unit_node */
 			struct _ast_node *slices;
+			usize slice_len;
 			struct _ast_node *captures;
-			int capture_len;
-			int slice_len;
+			usize capture_len;
 			struct _ast_node* body;
 		} fr; // for
 		struct {
diff --git a/sema.c b/sema.c
index ea4cf10..a1499a4 100644
--- a/sema.c
+++ b/sema.c
@@ -18,6 +18,12 @@ static struct { char *key; type *value; } *type_reg;
 
 static struct { char *key; prototype *value; } *prototypes;
 
+static scope *global_scope = NULL;
+static scope *current_scope = NULL;
+static type *current_return = NULL;
+
+static bool in_loop = false;
+
 /* Print the error message and sync the parser. */
 static void error(ast_node *n, char *msg)
 {
@@ -170,6 +176,9 @@ static void register_struct(sema *s, char *name, type *t)
 			return;
 		}
 
+		char *n = intern_string(s, m->name, m->name_len);
+		shput(t->data.structure.member_types, n, m_type);
+
 		if (m_type->size == 0) {
 			error(m->type, "a struct member can't be of type `void`.");
 			return;
@@ -195,8 +204,6 @@ static void register_struct(sema *s, char *name, type *t)
 	}
 
 	t->size = offset;
-
-	printf("%ld\n", t->size);
 }
 
 static void register_union(sema *s, char *name, type *t)
@@ -206,6 +213,15 @@ static void register_union(sema *s, char *name, type *t)
 	member *m = t->data.structure.members;
 	while (m) {
 		type *m_type = get_type(s, m->type);
+		
+		if (!m_type) {
+			error(m->type, "unknown type.");
+			return;
+		}
+
+		char *n = intern_string(s, m->name, m->name_len);
+		shput(t->data.structure.member_types, n, m_type);
+
 		if (alignment < m_type->alignment) {
 			alignment = m_type->alignment;
 		}
@@ -299,6 +315,9 @@ static void create_prototype(sema *s, ast_node *node)
 {
 	prototype *p = arena_alloc(s->allocator, sizeof(prototype));
 	p->name = intern_string(s, node->expr.function.name, node->expr.function.name_len);
+	if (shget(prototypes, p->name)) {
+		error(node, "function already defined.");
+	}
 
 	member *m = node->expr.function.parameters;
 	while (m) {
@@ -316,6 +335,304 @@ static void create_prototype(sema *s, ast_node *node)
 	shput(prototypes, p->name, p);
 }
 
+static void push_scope(sema *s)
+{
+	scope *scp = arena_alloc(s->allocator, sizeof(scope));
+	scp->parent = current_scope;
+	current_scope = scp;
+}
+
+static void pop_scope(sema *s)
+{
+	current_scope = current_scope->parent;
+}
+
+static type *get_def(sema *s, char *name)
+{
+	scope *current = current_scope;
+	while (current) {
+		type *t = shget(current->defs, name);
+		if (t) return t;
+
+		current = current->parent;
+	}
+
+	return NULL;
+}
+
+static type *get_string_type(sema *s, ast_node *node)
+{
+	type *string_type = arena_alloc(s->allocator, sizeof(type));
+	string_type->tag = TYPE_PTR;
+	string_type->size = sizeof(usize);
+	string_type->alignment = sizeof(usize);
+	string_type->name = "slice";
+	string_type->data.slice.child = shget(type_reg, "u8");
+	string_type->data.slice.is_const = true;
+	string_type->data.slice.is_volatile = false;
+	string_type->data.slice.len = node->expr.string.len;
+	return string_type;
+}
+
+static type *get_range_type(sema *s, ast_node *node)
+{
+	type *range_type = arena_alloc(s->allocator, sizeof(type));
+	range_type->tag = TYPE_PTR;
+	range_type->size = sizeof(usize);
+	range_type->alignment = sizeof(usize);
+	range_type->name = "slice";
+	range_type->data.slice.child = shget(type_reg, "usize");
+	range_type->data.slice.is_const = true;
+	range_type->data.slice.is_volatile = false;
+	range_type->data.slice.len = node->expr.binary.right->expr.integer - node->expr.binary.left->expr.integer;
+	return range_type;
+}
+
+static type *get_expression_type(sema *s, ast_node *node);
+static type *get_access_type(sema *s, ast_node *node)
+{
+	type *t = get_expression_type(s, node->expr.access.expr);
+	ast_node *member = node->expr.access.member;
+	char *name_start = member->expr.string.start;
+	usize name_len = member->expr.string.len;
+	if (!t || (t->tag != TYPE_STRUCT && t->tag != TYPE_UNION)) {
+		error(node, "invalid expression.");
+		return NULL;
+	}
+	char *name = intern_string(s, name_start, name_len);
+	type *res = shget(t->data.structure.member_types, name);
+	if (!res) {
+		error(node, "struct doesn't have that member");
+		return NULL;
+	}
+
+	return res;
+}
+
+static type *get_identifier_type(sema *s, ast_node *node)
+{
+	char *name_start = node->expr.string.start;
+	usize name_len = node->expr.string.len;
+	type *t = get_def(s, intern_string(s, name_start, name_len));
+	if (!t) {
+		error(node, "unknown identifier.");
+	}
+	return t;
+}
+
+static bool match(type *t1, type *t2);
+
+static type *get_expression_type(sema *s, ast_node *node)
+{
+	if (!node) {
+		return shget(type_reg, "void");
+	}
+
+	type *t = NULL;
+	prototype *prot = NULL;
+	switch (node->type) {
+		case NODE_IDENTIFIER:
+			return get_identifier_type(s, node);
+		case NODE_INTEGER:
+			return shget(type_reg, "i32");
+		case NODE_FLOAT:
+			return shget(type_reg, "f64");
+		case NODE_STRING:
+			return get_string_type(s, node);
+		case NODE_CHAR:
+			return shget(type_reg, "u8");
+		case NODE_BOOL:
+			return shget(type_reg, "bool");
+		case NODE_CAST:
+			return get_type(s, node->expr.cast.type);
+		case NODE_POSTFIX:
+		case NODE_UNARY:
+			return get_expression_type(s, node->expr.unary.right);
+		case NODE_BINARY:
+			t = get_expression_type(s, node->expr.binary.left);
+			if (!t) return NULL;
+			if (!match(t, get_expression_type(s, node->expr.binary.right))) {
+				error(node, "type mismatch.");
+				return NULL;
+			}
+			if (node->expr.binary.operator >= OP_EQ) {
+				return shget(type_reg, "bool");
+			} else if (node->expr.binary.operator >= OP_ASSIGN && node->expr.binary.operator <= OP_MOD_EQ) {
+				return shget(type_reg, "void");
+			} else {
+				return t;
+			}
+		case NODE_RANGE:
+			return get_range_type(s, node);
+		case NODE_ARRAY_SUBSCRIPT:
+			t = get_expression_type(s, node->expr.subscript.expr);
+			switch (t->tag) {
+				case TYPE_SLICE:
+					return t->data.slice.child;
+				case TYPE_PTR:
+					return t->data.ptr.child;
+				default:
+					error(node, "only pointers and slices can be indexed.");
+					return NULL;
+			}
+		case NODE_CALL:
+			prot = shget(prototypes, intern_string(s, node->expr.call.name, node->expr.call.name_len));
+			if (!prot) {
+				error(node, "unknown function.");
+				return NULL;
+			}
+			return prot->type;
+		case NODE_ACCESS:
+			return get_access_type(s, node);
+		default:
+			return shget(type_reg, "void");
+	}
+}
+
+static bool match(type *t1, type *t2)
+{
+	if (!t1 || !t2) return false;
+	if (t1->tag != t2->tag) return false;
+
+	switch(t1->tag) {
+		case TYPE_VOID:
+		case TYPE_BOOL:
+			return true;
+		case TYPE_PTR:
+			return (t1->data.ptr.is_const == t2->data.ptr.is_const) && (t1->data.ptr.is_volatile == t2->data.ptr.is_volatile) && match(t1->data.ptr.child, t2->data.ptr.child);
+		case TYPE_SLICE:
+			return (t1->data.slice.is_const == t2->data.slice.is_const) && (t1->data.slice.is_volatile == t2->data.slice.is_volatile) && match(t1->data.slice.child, t2->data.slice.child) && t1->data.slice.len == t2->data.slice.len;
+		case TYPE_STRUCT:
+		case TYPE_UNION:
+			return t1 == t2;
+		case TYPE_INTEGER:
+		case TYPE_UINTEGER:
+			return t1->data.integer == t2->data.integer;
+		case TYPE_FLOAT:
+			return t1->data.flt == t2->data.flt;
+		case TYPE_ENUM:
+		case TYPE_GENERIC:
+			/* TODO */
+			return false;
+	}
+
+	return false;
+}
+
+static void check_statement(sema *s, ast_node *node);
+static void check_body(sema *s, ast_node *node)
+{
+	push_scope(s);
+
+	ast_node *current = node;
+	while (current && current->type == NODE_UNIT) {
+		check_statement(s, current->expr.unit_node.expr);
+		current = current->expr.unit_node.next;
+	}
+
+	pop_scope(s);
+}
+
+static void check_for(sema *s, ast_node *node)
+{
+	ast_node *slices = node->expr.fr.slices;
+	ast_node *captures = node->expr.fr.captures;
+
+	push_scope(s);
+
+	ast_node *current_capture = captures;
+	ast_node *current_slice = slices;
+
+	while (current_capture) {
+		type *c_type = get_expression_type(s, current_slice->expr.unit_node.expr);
+		char *c_name = intern_string(s, current_capture->expr.unit_node.expr->expr.string.start, current_capture->expr.unit_node.expr->expr.string.len);
+		shput(current_scope->defs, c_name, c_type);
+		current_capture = current_capture->expr.unit_node.next;
+		current_slice = current_slice->expr.unit_node.next;
+	}
+
+	ast_node *current = node->expr.fr.body;
+
+	in_loop = true;
+	while (current && current->type == NODE_UNIT) {
+		check_statement(s, current->expr.unit_node.expr);
+		current = current->expr.unit_node.next;
+	}
+	in_loop = false;
+
+	pop_scope(s);
+}
+
+static void check_statement(sema *s, ast_node *node)
+{
+	if (!node) return;
+
+	type *t = NULL;
+	char *name = NULL;
+	switch(node->type) {
+		case NODE_RETURN:
+			if (!match(get_expression_type(s, node->expr.ret.value), current_return)) {
+				error(node, "return type doesn't match function's one.");
+			}
+			break;
+		case NODE_BREAK:
+			if (!in_loop) {
+				error(node, "`break` isn't in a loop.");
+			}
+			break;
+		case NODE_WHILE:
+			if (!match(get_expression_type(s, node->expr.whle.condition), shget(type_reg, "bool"))) {
+				error(node, "expected boolean value.");
+				return;
+			}
+
+			in_loop = true;
+			check_body(s, node->expr.whle.body);
+			in_loop = false;
+			break;
+		case NODE_FOR:
+			check_for(s, node);
+			break;
+		case NODE_VAR_DECL:
+			t = get_type(s, node->expr.var_decl.type);
+			name = intern_string(s, node->expr.var_decl.name, node->expr.var_decl.name_len);
+			if (get_def(s, name)) {
+				error(node, "redeclaration of variable.");
+				break;
+			}
+			if (!match(t, get_expression_type(s, node->expr.var_decl.value))) {
+				error(node, "type mismatch.");
+			}
+			shput(current_scope->defs, name, t);
+			break;
+		default:
+			get_expression_type(s, node);
+			break;
+	}
+}
+
+static void check_function(sema *s, ast_node *f)
+{
+	push_scope(s);
+	current_return = get_type(s, f->expr.function.type);
+
+	member *param = f->expr.function.parameters;
+	while (param) {
+		type *p_type = get_type(s, param->type);
+		char *t_name = intern_string(s, param->name, param->name_len);
+		shput(current_scope->defs, t_name, p_type);
+		param = param->next;
+	}
+
+	ast_node *current = f->expr.function.body;
+	while (current && current->type == NODE_UNIT) {
+		check_statement(s, current->expr.unit_node.expr);
+		current = current->expr.unit_node.next;
+	}
+
+	pop_scope(s);
+}
+
 static void analyze_unit(sema *s, ast_node *node)
 {
 	ast_node *current = node;
@@ -334,8 +651,12 @@ static void analyze_unit(sema *s, ast_node *node)
 		current = current->expr.unit_node.next;
 	}
 
-	for (int i=0; i < shlen(prototypes); i++) {
-		printf("f: %s\n", prototypes[i].key);
+	current = node;
+	while (current && current->type == NODE_UNIT) {
+		if (current->expr.unit_node.expr->type == NODE_FUNCTION) {
+			check_function(s, current->expr.unit_node.expr);
+		}
+		current = current->expr.unit_node.next;
 	}
 }
 
@@ -346,7 +667,13 @@ sema *sema_init(parser *p, arena *a)
 	types = NULL;
 	s->ast = p->ast;
 
+	global_scope = arena_alloc(a, sizeof(scope));
+	global_scope->parent = NULL;
+	global_scope->defs = NULL;
+	current_scope = global_scope;
+
 	register_type(s, "void", create_integer(s, "void", 0, false));
+	register_type(s, "bool", create_integer(s, "bool", 8, false));
 	register_type(s, "u8", create_integer(s, "u8", 8, false));
 	register_type(s, "u16", create_integer(s, "u16", 16, false));
 	register_type(s, "u32", create_integer(s, "u32", 32, false));
diff --git a/sema.h b/sema.h
index 9c27332..47832b7 100644
--- a/sema.h
+++ b/sema.h
@@ -8,6 +8,7 @@
 
 typedef enum {
 	TYPE_VOID,
+	TYPE_BOOL,
 	TYPE_PTR,
 	TYPE_SLICE,
 	TYPE_FLOAT,
@@ -42,6 +43,7 @@ typedef struct _type {
 			char *name;
 			usize name_len;
 			member *members;
+			struct { char *key; struct _type *value; } *member_types;
 		} structure;
 		struct {
 			char *name;
@@ -57,6 +59,11 @@ typedef struct {
 	type **parameters;
 } prototype;
 
+typedef struct _scope {
+	struct _scope *parent;
+	struct { char *key; type *value; } *defs;
+} scope;
+
 typedef struct {
 	arena *allocator;
 	ast_node *ast;