diff --git a/parser.c b/parser.c
index 9b7d8bc..89d2ede 100644
--- a/parser.c
+++ b/parser.c
@@ -11,6 +11,7 @@ void lexer_construct(Lexer* lexer, const char* text, size_t length)
         .index = 0,
         .line = 1,
         .col = 1,
+        .failed = false,
     };
 }
 
@@ -25,6 +26,36 @@ static inline bool is_id_char(char c)
         || (c >= '0' && c <= '9') || c == '_';
 }
 
+static inline Token skip_comment(Lexer* lexer)
+{
+    Pos pos = lexer_pos(lexer);
+    lexer_step(lexer);
+    if (lexer_current(lexer) == '/') {
+        while (!lexer_done(lexer) && lexer_current(lexer) != '\n') {
+            lexer_step(lexer);
+        }
+        return lexer_next(lexer);
+    } else if (lexer_current(lexer) == '*') {
+        lexer_step(lexer);
+        char last = '\0';
+        while (!lexer_done(lexer)
+            && !(last == '*' && lexer_current(lexer) == '/')) {
+            last = lexer_current(lexer);
+            lexer_step(lexer);
+        }
+        if (lexer_done(lexer)) {
+            lexer->failed = true;
+            print_error("lexer: malformed multiline comment", pos);
+            return lexer_token(lexer, TokenType_Error, pos);
+        }
+        return lexer_next(lexer);
+    } else {
+        lexer->failed = true;
+        print_error("lexer: malformed comment", pos);
+        return lexer_token(lexer, TokenType_Error, pos);
+    }
+}
+
 struct MatchIdToTokenTypeCase {
     const char* keyword;
     TokenType token_type;
@@ -41,6 +72,49 @@ static inline TokenType match_id_to_token_type(
     return TokenType_Id;
 }
 
+static inline Token lex_id_or_keyword(Lexer* lexer)
+{
+    Pos pos = lexer_pos(lexer);
+    lexer_step(lexer);
+    while (!lexer_done(lexer) && is_id_char(lexer_current(lexer))) {
+        lexer_step(lexer);
+    }
+    size_t length = lexer->index - pos.index;
+    TokenType token_type
+        = match_id_to_token_type(&lexer->text[pos.index], length,
+            (struct MatchIdToTokenTypeCase[]) {
+                { "not", TokenType_Not },
+                { "and", TokenType_And },
+                { "or", TokenType_Or },
+                { "if", TokenType_If },
+                { "loop", TokenType_Loop },
+                { "fn", TokenType_Fn },
+                { "return", TokenType_Return },
+                { "break", TokenType_Break },
+                { NULL, TokenType_Id },
+            });
+    return lexer_token(lexer, token_type, pos);
+}
+
+Token lex_single_char(Lexer* lexer, TokenType token_type)
+{
+    Pos pos = lexer_pos(lexer);
+    lexer_step(lexer);
+    return lexer_token(lexer, token_type, pos);
+}
+
+Token lex_single_or_double_char(
+    Lexer* lexer, TokenType first, char c2, TokenType second)
+{
+    Pos pos = lexer_pos(lexer);
+    lexer_step(lexer);
+    if (lexer_done(lexer) || lexer_current(lexer) != c2) {
+        return lexer_token(lexer, first, pos);
+    }
+    lexer_step(lexer);
+    return lexer_token(lexer, second, pos);
+}
+
 Token lexer_next(Lexer* lexer)
 {
     Pos pos = lexer_pos(lexer);
@@ -52,36 +126,70 @@ Token lexer_next(Lexer* lexer)
         lexer_step(lexer);
         return lexer_next(lexer);
     }
+    if (c == '/') {
+        return skip_comment(lexer);
+    }
     if (is_id_start_char(c)) {
-        lexer_step(lexer);
-        while (is_id_char(c)) {
-            lexer_step(lexer);
-        }
-        size_t length = lexer->index - pos.index;
-        TokenType token_type
-            = match_id_to_token_type(&lexer->text[pos.index], length,
-                (struct MatchIdToTokenTypeCase[]) {
-                    { "not", TokenType_Not },
-                    { "and", TokenType_And },
-                    { "or", TokenType_Or },
-                    { "loop", TokenType_Loop },
-                    { "fn", TokenType_Fn },
-                    { "return", TokenType_Return },
-                    { "break", TokenType_Break },
-                    { NULL, TokenType_Id },
-                });
-        return lexer_token(lexer, token_type, pos);
+        return lex_id_or_keyword(lexer);
     }
     if (c >= '1' && c <= '9') {
         lexer_step(lexer);
-        while (c >= '1' && c <= '9') {
+        while (!lexer_done(lexer) && c >= '1' && c <= '9') {
             lexer_step(lexer);
         }
         return lexer_token(lexer, TokenType_Int, pos);
     }
+    switch (c) {
+        case '0':
+            return lex_single_char(lexer, TokenType_Int);
+        case '(':
+            return lex_single_char(lexer, TokenType_LParen);
+        case ')':
+            return lex_single_char(lexer, TokenType_RParen);
+        case '{':
+            return lex_single_char(lexer, TokenType_LBrace);
+        case '}':
+            return lex_single_char(lexer, TokenType_RBrace);
+        case '[':
+            return lex_single_char(lexer, TokenType_LBracket);
+        case ']':
+            return lex_single_char(lexer, TokenType_RBracket);
+        case ',':
+            return lex_single_char(lexer, TokenType_Comma);
+        case ';':
+            return lex_single_char(lexer, TokenType_Semicolon);
+        case '+':
+            return lex_single_or_double_char(
+                lexer, TokenType_Plus, '=', TokenType_PlusEqual);
+        case '-':
+            return lex_single_or_double_char(
+                lexer, TokenType_Minus, '=', TokenType_MinusEqual);
+        case '*':
+            return lex_single_or_double_char(
+                lexer, TokenType_Asterisk, '=', TokenType_AsteriskEqual);
+        case '=':
+            return lex_single_or_double_char(
+                lexer, TokenType_Equal, '=', TokenType_EqualEqual);
+        case '!':
+            return lex_single_or_double_char(
+                lexer, TokenType_Exclamation, '=', TokenType_ExclamationEqual);
+        case '<':
+            return lex_single_or_double_char(
+                lexer, TokenType_LT, '=', TokenType_LTEqual);
+        case '>':
+            return lex_single_or_double_char(
+                lexer, TokenType_GT, '=', TokenType_GTEqual);
+        case '|':
+            return lex_single_or_double_char(
+                lexer, TokenType_Pipe, '>', TokenType_PipeGT);
+    }
+    lexer->failed = true;
+    print_error("lexer: unrecognized character", pos);
     return lexer_token(lexer, TokenType_Error, pos);
 }
 
+bool lexer_failed(const Lexer* lexer) { return lexer->failed; }
+
 Token lexer_token(Lexer* lexer, TokenType token_type, Pos pos)
 {
     return (Token) {
@@ -156,3 +264,200 @@ int ast_node_vec_push(ASTNodeVec* vec, ASTNode* item)
     vec->length += 1;
     return 0;
 }
+
+ASTNode* ast_node_new(ASTNodeType node_type, Pos pos, ASTNode spec_init)
+{
+    ASTNode* node = malloc(sizeof(ASTNode));
+    if (node == NULL) {
+        return NULL;
+    }
+    *node = spec_init;
+    node->node_type = node_type;
+    node->pos = pos;
+    return node;
+}
+
+void ast_node_free(ASTNode* node)
+{
+    if (node == NULL) {
+        return;
+    }
+    switch (node->node_type) {
+        case ASTNodeType_Error:
+            break;
+        case ASTNodeType_Id:
+            if (node->id_value != NULL) {
+                free(node->id_value);
+            }
+            break;
+        case ASTNodeType_Int:
+            break;
+        case ASTNodeType_Block:
+            for (size_t i = 0; i < node->statements.length; ++i) {
+                ast_node_free(node->statements.data[i]);
+            }
+            ast_node_vec_destroy(&node->statements);
+            break;
+        case ASTNodeType_If:
+            ast_node_free(node->if_node.condition);
+            ast_node_free(node->if_node.truthy);
+            ast_node_free(node->if_node.falsy);
+            break;
+        case ASTNodeType_Loop:
+            ast_node_free(node->loop_node.body);
+            break;
+        case ASTNodeType_Call:
+            ast_node_free(node->call_node.subject);
+            for (size_t i = 0; i < node->call_node.args.length; ++i) {
+                ast_node_free(node->call_node.args.data[i]);
+            }
+            ast_node_vec_destroy(&node->call_node.args);
+            break;
+        case ASTNodeType_Index:
+            ast_node_free(node->index_node.subject);
+            ast_node_free(node->index_node.value);
+            break;
+        case ASTNodeType_Unary:
+            ast_node_free(node->unary_node.subject);
+            break;
+        case ASTNodeType_Binary:
+            ast_node_free(node->binary_node.left);
+            ast_node_free(node->binary_node.right);
+            break;
+        case ASTNodeType_Assign:
+            ast_node_free(node->assign_node.subject);
+            ast_node_free(node->assign_node.value);
+            break;
+        case ASTNodeType_Let:
+            if (node->let_node.id != NULL) {
+                free(node->let_node.id);
+            }
+            ast_node_free(node->let_node.value);
+            break;
+        case ASTNodeType_Break:
+            break;
+        case ASTNodeType_Fn:
+            if (node->fn_node.id != NULL) {
+                free(node->fn_node.id);
+            }
+            for (size_t i = 0; i < node->fn_node.params.length; ++i) {
+                ast_node_free(node->fn_node.params.data[i]);
+            }
+            ast_node_vec_destroy(&node->fn_node.params);
+            ast_node_free(node->fn_node.body);
+            break;
+    }
+    free(node);
+}
+
+void parser_construct(Parser* parser, const char* text, size_t text_length)
+{
+    *parser = (Parser) {
+        .text = text,
+        .text_length = text_length,
+        .lexer = { 0 },
+        .current = { 0 },
+        .failed = false,
+    };
+    lexer_construct(&parser->lexer, text, text_length);
+    parser->current = lexer_next(&parser->lexer);
+}
+
+bool parser_failed(const Parser* parser) { return parser->failed; }
+
+void parser_step(Parser* parser)
+{
+    parser->current = lexer_next(&parser->lexer);
+}
+
+bool parser_done(const Parser* parser)
+{
+    return parser->current.token_type == TokenType_EOF;
+}
+
+ASTNode* parser_parse(Parser* parser) { return parser_parse_expr(parser); }
+
+ASTNode* parser_parse_expr(Parser* parser)
+{
+    return parser_parse_operand(parser);
+}
+
+ASTNode* parser_parse_operand(Parser* parser)
+{
+    Pos pos = parser->current.pos;
+    switch (parser->current.token_type) {
+        case TokenType_Error:
+            return ast_node_new(ASTNodeType_Error, pos, (ASTNode) { 0 });
+        case TokenType_Id:
+            return parser_parse_id(parser);
+        case TokenType_Int:
+            return parser_parse_int(parser);
+        case TokenType_LParen:
+        case TokenType_LBrace:
+        case TokenType_If:
+        case TokenType_Loop:
+        default:
+            parser->failed = true;
+            print_error("expected operand", pos);
+            return ast_node_new(ASTNodeType_Error, pos, (ASTNode) { 0 });
+            break;
+    }
+}
+
+ASTNode* parser_parse_id(Parser* parser)
+{
+    Pos pos = parser->current.pos;
+    char* value = malloc(parser->current.length + 1);
+    value[parser->current.length] = '\0';
+    strncpy(value, &parser->text[parser->current.pos.index],
+        parser->current.length);
+    parser_step(parser);
+    return ast_node_new(ASTNodeType_Id, pos, (ASTNode) { .id_value = value });
+}
+
+ASTNode* parser_parse_int(Parser* parser)
+{
+    Pos pos = parser->current.pos;
+    int value = (int)strtol(&parser->text[parser->current.length], NULL, 10);
+    parser_step(parser);
+    return ast_node_new(ASTNodeType_Int, pos, (ASTNode) { .int_value = value });
+}
+
+ASTNode* parser_parse_group(Parser* parser)
+{
+    Pos pos = parser->current.pos;
+    parser_step(parser);
+    ASTNode* expr = parser_parse_expr(parser);
+    if (parser->current.token_type != TokenType_RParen) {
+        parser->failed = true;
+        print_error("parser: expected ')'", pos);
+        return ast_node_new(ASTNodeType_Error, pos, (ASTNode) { 0 });
+    }
+    parser_step(parser);
+    return expr;
+}
+
+ASTNode* parser_parse_block(Parser* parser)
+{
+    Pos pos = parser->current.pos;
+    parser_step(parser);
+    ASTNodeVec statements;
+    ast_node_vec_construct(&statements);
+    while (!parser_done(parser)
+        && parser->current.token_type != TokenType_RBrace) {
+        ASTNode* statement = parser_parse_statement(parser);
+        ast_node_vec_push(&statements, statement);
+    }
+    if (parser->current.token_type != TokenType_RBrace) {
+        parser->failed = true;
+        print_error("parser: expected '}'", pos);
+        return ast_node_new(ASTNodeType_Error, pos, (ASTNode) { 0 });
+    }
+    parser_step(parser);
+    return ast_node_new(
+        ASTNodeType_Block, pos, (ASTNode) { .statements = statements });
+}
+
+ASTNode* parser_parse_if(Parser* parser);
+
+ASTNode* parser_parse_loop(Parser* parser);
diff --git a/parser.h b/parser.h
index 8d5594b..955cef0 100644
--- a/parser.h
+++ b/parser.h
@@ -10,6 +10,8 @@ typedef struct {
     int col;
 } Pos;
 
+void print_error(const char* message, Pos pos);
+
 typedef enum {
     TokenType_Error,
     TokenType_EOF,
@@ -18,6 +20,7 @@ typedef enum {
     TokenType_Not,
     TokenType_And,
     TokenType_Or,
+    TokenType_If,
     TokenType_Loop,
     TokenType_Fn,
     TokenType_Return,
@@ -36,13 +39,14 @@ typedef enum {
     TokenType_MinusEqual,
     TokenType_Asterisk,
     TokenType_AsteriskEqual,
+    TokenType_Equal,
     TokenType_EqualEqual,
     TokenType_Exclamation,
     TokenType_ExclamationEqual,
     TokenType_LT,
-    TokenType_LTE,
+    TokenType_LTEqual,
     TokenType_GT,
-    TokenType_GTE,
+    TokenType_GTEqual,
     TokenType_Pipe,
     TokenType_PipeGT,
 } TokenType;
@@ -59,10 +63,12 @@ typedef struct {
     size_t index;
     int line;
     int col;
+    bool failed;
 } Lexer;
 
 void lexer_construct(Lexer* lexer, const char* text, size_t text_length);
 Token lexer_next(Lexer* lexer);
+bool lexer_failed(const Lexer* lexer);
 Token lexer_token(Lexer* lexer, TokenType token_type, Pos pos);
 void lexer_step(Lexer* lexer);
 bool lexer_done(const Lexer* lexer);
@@ -174,7 +180,7 @@ typedef struct {
 
 struct ASTNode {
     ASTNodeType node_type;
-    int line;
+    Pos pos;
     union {
         char* id_value;
         int int_value;
@@ -191,6 +197,30 @@ struct ASTNode {
     };
 };
 
-void ast_node_destroy(ASTNode* node);
+ASTNode* ast_node_new(ASTNodeType node_type, Pos pos, ASTNode spec_init);
+void ast_node_free(ASTNode* node);
+
+typedef struct {
+    const char* text;
+    size_t text_length;
+    Lexer lexer;
+    Token current;
+    bool failed;
+} Parser;
+
+void parser_construct(Parser* parser, const char* text, size_t text_length);
+bool parser_failed(const Parser* parser);
+void parser_step(Parser* parser);
+bool parser_done(const Parser* parser);
+ASTNode* parser_parse(Parser* parser);
+ASTNode* parser_parse_statement(Parser* parser);
+ASTNode* parser_parse_expr(Parser* parser);
+ASTNode* parser_parse_operand(Parser* parser);
+ASTNode* parser_parse_id(Parser* parser);
+ASTNode* parser_parse_int(Parser* parser);
+ASTNode* parser_parse_group(Parser* parser);
+ASTNode* parser_parse_block(Parser* parser);
+ASTNode* parser_parse_if(Parser* parser);
+ASTNode* parser_parse_loop(Parser* parser);
 
 #endif