diff --git a/lib/expr.ml b/lib/expr.ml
index 3cfad5b..52c355f 100644
--- a/lib/expr.ml
+++ b/lib/expr.ml
@@ -23,13 +23,15 @@ type binary_op =
 [@@deriving show { with_path = false }]
 
 type unary_op = Neg | Not [@@deriving show { with_path = false }]
+type logical_op = And | Or [@@deriving show { with_path = false }]
 
 type expr =
   | Literal of literal
   | Variable of string
   | Assignment of { name : string; expr : expr_node }
-  | BinaryExpr of { op : binary_op; left : expr_node; right : expr_node }
-  | UnaryExpr of { op : unary_op; expr : expr_node }
+  | Unary of { op : unary_op; expr : expr_node }
+  | Binary of { op : binary_op; left : expr_node; right : expr_node }
+  | Logical of { op : logical_op; left : expr_node; right : expr_node }
 
 and expr_node = { expr : expr; pos : Error.code_pos }
 
@@ -39,11 +41,14 @@ let rec show_expr ?(indent = 0) expr =
   match expr with
   | Literal literal -> indent_s ^ show_literal literal
   | Variable name -> indent_s ^ "Variable " ^ name
-  | Assignment { name; expr } -> indent_s ^ name ^ " = \n" ^ show_expr expr.expr ~indent:(indent + 2)
-  | BinaryExpr { op; left; right } ->
+  | Assignment { name; expr } -> indent_s ^ name ^ " = \n" ^ show_indented expr.expr
+  | Unary { op; expr } -> indent_s ^ show_unary_op op ^ "\n" ^ show_indented expr.expr
+  | Binary { op; left; right } ->
       indent_s ^ show_binary_op op ^ "\n" ^ show_indented left.expr ^ "\n"
       ^ show_indented right.expr
-  | UnaryExpr { op; expr } -> indent_s ^ show_unary_op op ^ "\n" ^ show_indented expr.expr
+  | Logical { op; left; right } ->
+      indent_s ^ show_logical_op op ^ "\n" ^ show_indented left.expr ^ "\n"
+      ^ show_indented right.expr
 
 let show_expr_node expr_node = show_expr expr_node.expr
 let make_expr_node (pos : Error.code_pos) (expr : expr) : expr_node = { expr; pos }
@@ -63,8 +68,11 @@ let make_variable (pos : Error.code_pos) (name : string) : expr_node =
 let make_assignment (pos : Error.code_pos) (name : string) (expr : expr_node) : expr_node =
   Assignment { name; expr } |> make_expr_node pos
 
-let make_binary (pos : Error.code_pos) (op : binary_op) (left : expr_node) (right : expr_node) =
-  make_expr_node pos (BinaryExpr { op; left; right })
-
 let make_unary (pos : Error.code_pos) (op : unary_op) (expr : expr_node) =
-  make_expr_node pos (UnaryExpr { op; expr })
+  Unary { op; expr } |> make_expr_node pos
+
+let make_binary (pos : Error.code_pos) (op : binary_op) (left : expr_node) (right : expr_node) =
+  Binary { op; left; right } |> make_expr_node pos
+
+let make_logical (pos : Error.code_pos) (op : logical_op) (left : expr_node) (right : expr_node) =
+  Logical { op; left; right } |> make_expr_node pos
diff --git a/lib/interpreter.ml b/lib/interpreter.ml
index f6d6fa5..bf25e15 100644
--- a/lib/interpreter.ml
+++ b/lib/interpreter.ml
@@ -28,7 +28,18 @@ let rec interpret_expr (env : environment) (expr : expr_node) : (lox_value, runt
         let* value = interpret_expr env expr in
         Env.update env name value;
         Ok value
-  | BinaryExpr { op; left; right } -> (
+  | Unary { op; expr } -> (
+      let* expr = interpret_expr env expr in
+      match (op, expr) with
+      | Neg, Number x -> Ok (Number (-.x))
+      | Not, Bool b -> Ok (Bool (not b))
+      | _, _ ->
+          let msg =
+            Printf.sprintf "Invalid operant of type %s to operator %s"
+              (type_string_of_lox_value expr) (show_unary_op op)
+          in
+          Error (RuntimeError.make pos msg))
+  | Binary { op; left; right } -> (
       let* left = interpret_expr env left in
       let* right = interpret_expr env right in
       match (left, op, right) with
@@ -58,17 +69,11 @@ let rec interpret_expr (env : environment) (expr : expr_node) : (lox_value, runt
               (type_string_of_lox_value left) (type_string_of_lox_value right) (show_binary_op op)
           in
           Error { pos; msg })
-  | UnaryExpr { op; expr } -> (
-      let* expr = interpret_expr env expr in
-      match (op, expr) with
-      | Neg, Number x -> Ok (Number (-.x))
-      | Not, Bool b -> Ok (Bool (not b))
-      | _, _ ->
-          let msg =
-            Printf.sprintf "Invalid operant of type %s to operator %s"
-              (type_string_of_lox_value expr) (show_unary_op op)
-          in
-          Error (RuntimeError.make pos msg))
+  | Logical { op; left; right } -> (
+      let* left = interpret_expr env left in
+      match (op, lox_value_to_bool left) with
+      | And, false | Or, true -> Ok left (* short circuit *)
+      | _ -> interpret_expr env right)
 
 let rec interpret_stmt (env : environment) (stmt : stmt_node) : (unit, runtime_error) result =
   let { pos; stmt } = stmt in
@@ -98,3 +103,8 @@ let rec interpret_stmt (env : environment) (stmt : stmt_node) : (unit, runtime_e
         | [] -> Ok ()
       in
       _interpret stmts
+  | If { cond; then_; else_ } ->
+      let* cond = interpret_expr env cond in
+      let cond = lox_value_to_bool cond in
+      if cond then interpret_stmt env then_
+      else Option.map (interpret_stmt env) else_ |> Option.value ~default:(Ok ())
diff --git a/lib/parser.ml b/lib/parser.ml
index cc8e10b..9e950d7 100644
--- a/lib/parser.ml
+++ b/lib/parser.ml
@@ -35,7 +35,7 @@ let consume state tt =
     let pos = cur_pos state in
     let tt' = peek_tt state in
     let msg = Printf.sprintf "Expected %s, but got %s" (show_token_type tt) (show_token_type tt') in
-    Error (ParserError.make pos msg)
+    ParserError.make pos msg |> Result.error
 
 let consume_identifier state =
   match peek_tt state with
@@ -44,15 +44,15 @@ let consume_identifier state =
       Ok name
   | tt ->
       let pos = cur_pos state in
-      let msg = Printf.sprintf "Expected iedntifier, but got %s" (show_token_type tt) in
-      Error (ParserError.make pos msg)
+      let msg = Printf.sprintf "Expected identifier, but got %s" (show_token_type tt) in
+      ParserError.make pos msg |> Result.error
 
 let matches state tts =
   let f = ( = ) (peek_tt state) in
   Array.fold_left (fun acc tt -> acc || f tt) false tts
 
 let collect_chain (state : state ref) (tts : token_type array)
-    (higher_prec : state ref -> expr_result) : ((expr_node * token) array, parser_error) result =
+    (higher_prec : state ref -> expr_result) : ((expr_node * token) list, parser_error) result =
   let rec collect_chain_rec (acc : (expr_node * token) list) =
     if (not (is_at_end state)) && matches state tts then
       let token = next state in
@@ -61,29 +61,29 @@ let collect_chain (state : state ref) (tts : token_type array)
       collect_chain_rec acc
     else Ok acc
   in
-  collect_chain_rec [] |> Result.map (fun l -> Array.of_list (List.rev l))
+  collect_chain_rec [] |> Result.map (fun l -> List.rev l)
 
 let primary (state : state ref) : expr_result =
   let pos = cur_pos state in
   match peek_tt state with
   | Number x ->
       advance state;
-      Ok (make_number pos x)
+      make_number pos x |> Result.ok
   | String s ->
       advance state;
-      Ok (make_string pos s)
+      make_string pos s |> Result.ok
   | True ->
       advance state;
-      Ok (make_bool pos true)
+      make_bool pos true |> Result.ok
   | False ->
       advance state;
-      Ok (make_bool pos false)
+      make_bool pos false |> Result.ok
   | Nil ->
       advance state;
-      Ok (make_nil pos)
+      make_nil pos |> Result.ok
   | Identifier name ->
       advance state;
-      Ok (make_variable pos name)
+      make_variable pos name |> Result.ok
   | tt ->
       advance state;
       let msg = Printf.sprintf "Expected valid expression, got %s instead" (show_token_type tt) in
@@ -129,7 +129,7 @@ and mul_or_div (state : state ref) : expr_result =
     in
     make_binary pos op acc expr
   in
-  let expr = Array.fold_left f expr exprs_tokens in
+  let expr = List.fold_left f expr exprs_tokens in
   Ok expr
 
 and sum_or_diff (state : state ref) : expr_result =
@@ -145,7 +145,7 @@ and sum_or_diff (state : state ref) : expr_result =
     in
     make_binary pos op acc expr
   in
-  let expr = Array.fold_left f expr exprs_tokens in
+  let expr = List.fold_left f expr exprs_tokens in
   Ok expr
 
 and inequality (state : state ref) : expr_result =
@@ -166,7 +166,7 @@ and inequality (state : state ref) : expr_result =
     in
     make_binary pos op acc expr
   in
-  let expr = Array.fold_left f expr exprs_tokens in
+  let expr = List.fold_left f expr exprs_tokens in
   Ok expr
 
 and equality (state : state ref) : expr_result =
@@ -181,19 +181,41 @@ and equality (state : state ref) : expr_result =
         make_unary pos Not expr
     | _ -> assert false (* should only be here if tt is == != *)
   in
-  let expr = Array.fold_left f expr exprs_tokens in
+  let expr = List.fold_left f expr exprs_tokens in
+  Ok expr
+
+and logical_and (state : state ref) : expr_result =
+  let* expr = equality state in
+  let* exprs_tokens = collect_chain state [| And |] equality in
+  let f acc (expr, (token : token)) =
+    let pos = token.pos in
+    assert (token.token_type = And);
+    make_logical pos And acc expr
+  in
+  let expr = List.fold_left f expr exprs_tokens in
+  Ok expr
+
+and logical_or (state : state ref) : expr_result =
+  let* expr = logical_and state in
+  let* exprs_tokens = collect_chain state [| Or |] logical_and in
+  let f acc (expr, (token : token)) =
+    let pos = token.pos in
+    assert (token.token_type = Or);
+    make_logical pos Or acc expr
+  in
+  let expr = List.fold_left f expr exprs_tokens in
   Ok expr
 
 and assignment (state : state ref) : expr_result =
-  let* expr = equality state in
+  let* expr = logical_or state in
   if Equal = peek_tt state then
     let pos = (next state).pos in
     let* rhs = assignment state in
     match expr.expr with
-    | Variable name -> Ok (make_assignment pos name rhs)
+    | Variable name -> make_assignment pos name rhs |> Result.ok
     | _ ->
         let msg = "Invalid assignment target" in
-        Error (ParserError.make pos msg)
+        ParserError.make pos msg |> Result.error
   else Ok expr
 
 and expression (state : state ref) : expr_result = assignment state
@@ -204,7 +226,7 @@ let rec block (state : state ref) : stmt_result =
   let rec collect_stmts state =
     if is_at_end state then
       let msg = "Unterminated block" in
-      Error (ParserError.make pos msg)
+      ParserError.make pos msg |> Result.error
     else
       match peek_tt state with
       | RightBrace -> Ok []
@@ -215,7 +237,19 @@ let rec block (state : state ref) : stmt_result =
   in
   let* stmts = collect_stmts state in
   let* _ = consume state RightBrace in
-  Ok (make_block pos stmts)
+  make_block pos stmts |> Result.ok
+
+and if_then_else (state : state ref) : stmt_result =
+  let pos = cur_pos state in
+  let* _ = consume state If in
+  let* _ = consume state LeftParen in
+  let* cond = expression state in
+  let* _ = consume state RightParen in
+  let* then_ = statement state in
+  let* (else_ : stmt_node option) =
+    if advance_if state Else then statement state |> Result.map Option.some else Ok None
+  in
+  make_if pos cond then_ else_ |> Result.ok
 
 and statement (state : state ref) : stmt_result =
   let pos = cur_pos state in
@@ -227,6 +261,7 @@ and statement (state : state ref) : stmt_result =
       let stmt = make_print pos expr in
       Ok stmt
   | LeftBrace -> block state
+  | If -> if_then_else state
   | _ ->
       let* expr = expression state in
       let* _ = consume state Semicolon in
@@ -248,7 +283,7 @@ and var_declaration (state : state ref) : stmt_result =
       Ok None
   in
   let* _ = consume state Semicolon in
-  Ok (make_var_decl pos name init)
+  make_var_decl pos name init |> Result.ok
 
 and declaration (state : state ref) : stmt_result =
   match peek_tt state with Var -> var_declaration state | _ -> statement state
@@ -270,7 +305,6 @@ let rec parse_impl (state : state ref) : parse_result =
         let* stmts = parse_impl state in
         Ok (stmt :: stmts)
     | Error e -> (
-        print_endline e.msg;
         synchronise state;
         if peek_tt state = Eof then Error [ e ]
         else
diff --git a/lib/stmt.ml b/lib/stmt.ml
index bcaca44..15c9598 100644
--- a/lib/stmt.ml
+++ b/lib/stmt.ml
@@ -5,40 +5,47 @@ type stmt =
   | Print of expr_node
   | VarDecl of { name : string; init : expr_node option }
   | Block of stmt_node list
+  | If of { cond : expr_node; then_ : stmt_node; else_ : stmt_node option }
 
 and stmt_node = { stmt : stmt; pos : Error.code_pos }
 
 let rec show_stmt ?(indent = 0) stmt =
   let indent_s = String.make indent ' ' in
+  let show_expr_ind ?(depth = 2) = show_expr ~indent:(indent + depth) in
+  let show_stmt_ind ?(depth = 2) = show_stmt ~indent:(indent + depth) in
   match stmt with
-  | Expr expr -> indent_s ^ "Expr\n" ^ show_expr ~indent:(indent + 2) expr.expr
-  | Print expr -> indent_s ^ "Print\n" ^ show_expr ~indent:(indent + 2) expr.expr
+  | Expr expr -> indent_s ^ "Expr\n" ^ show_expr_ind expr.expr
+  | Print expr -> indent_s ^ "Print\n" ^ show_expr_ind expr.expr
   | VarDecl { name; init } -> (
       indent_s ^ "Var " ^ name
-      ^
-      match init with Some init -> " = \n" ^ show_expr ~indent:(indent + 2) init.expr | None -> "")
+      ^ match init with Some init -> " = \n" ^ show_expr_ind init.expr | None -> "")
   | Block stmts ->
       let stmts_s =
-        List.fold_left
-          (fun acc stmt -> acc ^ show_stmt ~indent:(indent + 2) stmt.stmt ^ "\n")
-          "" stmts
+        List.fold_left (fun acc stmt -> acc ^ show_stmt_ind stmt.stmt ^ "\n") "" stmts
       in
       "Block" ^ stmts_s ^ "End"
+  | If { cond; then_; else_ } ->
+      let cond_s = show_expr_ind cond.expr in
+      let then_s = show_stmt_ind ~depth:4 then_.stmt in
+      let else_s = Option.map (fun stmt -> show_stmt_ind ~depth:4 stmt.stmt) else_ in
+      indent_s ^ "If\n" ^ cond_s ^ "\n" ^ indent_s ^ "  Then\n" ^ then_s
+      ^ if Option.is_some else_s then "\n" ^ indent_s ^ "  Else\n" ^ Option.get else_s else ""
 
 let show_stmt_node stmt_node = show_stmt stmt_node.stmt
+let make_stmt_node (pos : Error.code_pos) (stmt : stmt) : stmt_node = { stmt; pos }
 
 let make_expr_stmt (pos : Error.code_pos) (expr : expr_node) : stmt_node =
-  let stmt = Expr expr in
-  { stmt; pos }
+  Expr expr |> make_stmt_node pos
 
 let make_print (pos : Error.code_pos) (expr : expr_node) : stmt_node =
-  let stmt = Print expr in
-  { stmt; pos }
+  Print expr |> make_stmt_node pos
 
 let make_var_decl (pos : Error.code_pos) (name : string) (init : expr_node option) =
-  let stmt = VarDecl { name; init } in
-  { stmt; pos }
+  VarDecl { name; init } |> make_stmt_node pos
 
 let make_block (pos : Error.code_pos) (stmts : stmt_node list) : stmt_node =
-  let stmt = Block stmts in
-  { stmt; pos }
+  Block stmts |> make_stmt_node pos
+
+let make_if (pos : Error.code_pos) (cond : expr_node) (then_ : stmt_node) (else_ : stmt_node option)
+    =
+  If { cond; then_; else_ } |> make_stmt_node pos
diff --git a/lib/value.ml b/lib/value.ml
index 75c7194..3fe9dde 100644
--- a/lib/value.ml
+++ b/lib/value.ml
@@ -14,3 +14,6 @@ let type_string_of_lox_value lox_value =
   | Number _ -> "Number"
   | Bool _ -> "Bool"
   | Nil -> "Nil"
+
+let lox_value_to_bool lox_value =
+  match lox_value with String _ -> true | Number _ -> true | Bool b -> b | Nil -> false