diff --git a/src/builtins/mod.rs b/src/builtins/mod.rs
index 4bcf81e..2fce24a 100644
--- a/src/builtins/mod.rs
+++ b/src/builtins/mod.rs
@@ -3,12 +3,12 @@ use std::rc::Rc;
 
 use crate::ty::common::Const;
 use crate::ty::internal::{AttrSet, PrimOp, Value};
-use crate::vm::{Env, VM};
+use crate::vm::{LetEnv, VM};
 
-pub fn env<'jit, 'vm>(vm: &'vm VM<'jit>) -> Env<'jit, 'vm> {
-    let mut env = Env::empty();
-    env.insert(vm.new_sym("true"), Value::Const(Const::Bool(true)));
-    env.insert(vm.new_sym("false"), Value::Const(Const::Bool(false)));
+pub fn env<'jit, 'vm>(vm: &'vm VM<'jit>) -> LetEnv<'jit, 'vm> {
+    let mut env_map = HashMap::new();
+    env_map.insert(vm.new_sym("true"), Value::Const(Const::Bool(true)));
+    env_map.insert(vm.new_sym("false"), Value::Const(Const::Bool(false)));
 
     let primops = [
         PrimOp::new("add", 2, |_, args| {
@@ -46,18 +46,19 @@ pub fn env<'jit, 'vm>(vm: &'vm VM<'jit>) -> Env<'jit, 'vm> {
     let mut map = HashMap::new();
     for primop in primops {
         let primop = Rc::new(primop);
-        env.insert(
+        env_map.insert(
             vm.new_sym(format!("__{}", primop.name)),
             Value::PrimOp(primop.clone()),
         );
         map.insert(vm.new_sym(primop.name), Value::PrimOp(primop));
     }
+    let sym = vm.new_sym("builtins");
     let attrs = Rc::new_cyclic(|weak| {
-        map.insert(vm.new_sym("builtins"), Value::Builtins(weak.clone()));
+        map.insert(sym, Value::Builtins(weak.clone()));
         AttrSet::from_inner(map)
     });
     let builtins = Value::AttrSet(attrs);
 
-    env.insert(vm.new_sym("builtins"), builtins);
-    env
+    env_map.insert(sym, builtins);
+    LetEnv::new(env_map.into())
 }
diff --git a/src/bytecode.rs b/src/bytecode.rs
index f156e22..537e461 100644
--- a/src/bytecode.rs
+++ b/src/bytecode.rs
@@ -33,8 +33,6 @@ pub enum OpCode {
 
     /// jump forward
     Jmp { step: usize },
-    /// [ .. cond ] consume 1 element, if `cond`` is true, then jump forward
-    JmpIfTrue { step: usize },
     /// [ .. cond ] consume 1 element, if `cond` is false, then jump forward
     JmpIfFalse { step: usize },
 
diff --git a/src/jit/helpers.rs b/src/jit/helpers.rs
index 4ece819..10d2bf9 100644
--- a/src/jit/helpers.rs
+++ b/src/jit/helpers.rs
@@ -1,5 +1,3 @@
-use std::rc::Rc;
-
 use inkwell::AddressSpace;
 use inkwell::context::Context;
 use inkwell::execution_engine::ExecutionEngine;
@@ -8,8 +6,8 @@ use inkwell::types::{FloatType, FunctionType, IntType, PointerType, StructType};
 use inkwell::values::{BasicValueEnum, FunctionValue};
 
 use crate::jit::JITValueData;
-use crate::ty::internal::Thunk;
-use crate::vm::{Env, VM};
+use crate::ty::internal::{Thunk, Value};
+use crate::vm::{LetEnv, VM};
 
 use super::{JITFunc, JITValue, ValueTag};
 
@@ -25,10 +23,14 @@ pub struct Helpers<'ctx> {
     pub debug: FunctionValue<'ctx>,
     pub capture_env: FunctionValue<'ctx>,
     pub neg: FunctionValue<'ctx>,
+    pub not: FunctionValue<'ctx>,
     pub add: FunctionValue<'ctx>,
     pub sub: FunctionValue<'ctx>,
+    pub eq: FunctionValue<'ctx>,
+    pub or: FunctionValue<'ctx>,
     pub call: FunctionValue<'ctx>,
     pub lookup: FunctionValue<'ctx>,
+    pub force: FunctionValue<'ctx>,
 }
 
 impl<'ctx> Helpers<'ctx> {
@@ -61,6 +63,11 @@ impl<'ctx> Helpers<'ctx> {
             value_type.fn_type(&[value_type.into(), ptr_type.into()], false),
             None,
         );
+        let not = module.add_function(
+            "not",
+            value_type.fn_type(&[value_type.into(), ptr_type.into()], false),
+            None,
+        );
         let add = module.add_function(
             "add",
             value_type.fn_type(&[value_type.into(), value_type.into()], false),
@@ -71,15 +78,23 @@ impl<'ctx> Helpers<'ctx> {
             value_type.fn_type(&[value_type.into(), value_type.into()], false),
             None,
         );
-        // Assuming a single argument for now based on the test case
+        let eq = module.add_function(
+            "eq",
+            value_type.fn_type(&[value_type.into(), value_type.into()], false),
+            None,
+        );
+        let or = module.add_function(
+            "or",
+            value_type.fn_type(&[value_type.into(), value_type.into()], false),
+            None,
+        );
         let call = module.add_function(
             "call",
             value_type.fn_type(
                 &[
-                    ptr_type.into(),
-                    ptr_type.into(),
-                    ptr_type.into(),
                     value_type.into(),
+                    value_type.into(),
+                    ptr_type.into(),
                 ],
                 false,
             ),
@@ -90,14 +105,23 @@ impl<'ctx> Helpers<'ctx> {
             value_type.fn_type(&[ptr_int_type.into(), ptr_type.into()], false),
             None,
         );
+        let force = module.add_function(
+            "force",
+            value_type.fn_type(&[value_type.into(), ptr_type.into()], false),
+            None,
+        );
 
         execution_engine.add_global_mapping(&debug, helper_debug as _);
         execution_engine.add_global_mapping(&capture_env, helper_capture_env as _);
         execution_engine.add_global_mapping(&neg, helper_neg as _);
+        execution_engine.add_global_mapping(&not, helper_not as _);
         execution_engine.add_global_mapping(&add, helper_add as _);
         execution_engine.add_global_mapping(&sub, helper_sub as _);
+        execution_engine.add_global_mapping(&eq, helper_eq as _);
+        execution_engine.add_global_mapping(&or, helper_or as _);
         execution_engine.add_global_mapping(&call, helper_call as _);
         execution_engine.add_global_mapping(&lookup, helper_lookup as _);
+        execution_engine.add_global_mapping(&force, helper_force as _);
 
         Helpers {
             int_type,
@@ -111,10 +135,14 @@ impl<'ctx> Helpers<'ctx> {
             debug,
             capture_env,
             neg,
+            not,
             add,
             sub,
+            eq,
+            or,
             call,
             lookup,
+            force
         }
     }
 
@@ -179,13 +207,13 @@ extern "C" fn helper_debug(value: JITValue) {
 }
 
 #[unsafe(no_mangle)]
-extern "C" fn helper_capture_env(thunk: JITValue, env: *const Env) {
+extern "C" fn helper_capture_env(thunk: JITValue, env: *const LetEnv) {
     let thunk: &Thunk = unsafe { std::mem::transmute(thunk.data.ptr.as_ref().unwrap()) };
     thunk.capture(unsafe { env.as_ref().unwrap() }.clone());
 }
 
 #[unsafe(no_mangle)]
-extern "C" fn helper_neg(rhs: JITValue, _env: *const Env) -> JITValue {
+extern "C" fn helper_neg(rhs: JITValue, _env: *const LetEnv) -> JITValue {
     use ValueTag::*;
     match rhs.tag {
         Int => JITValue {
@@ -198,6 +226,20 @@ extern "C" fn helper_neg(rhs: JITValue, _env: *const Env) -> JITValue {
     }
 }
 
+#[unsafe(no_mangle)]
+extern "C" fn helper_not(rhs: JITValue, _env: *const LetEnv) -> JITValue {
+    use ValueTag::*;
+    match rhs.tag {
+        Bool => JITValue {
+            tag: Bool,
+            data: JITValueData {
+                bool: !unsafe { rhs.data.bool },
+            },
+        },
+        _ => todo!(),
+    }
+}
+
 #[unsafe(no_mangle)]
 extern "C" fn helper_add(lhs: JITValue, rhs: JITValue) -> JITValue {
     use ValueTag::*;
@@ -235,20 +277,68 @@ extern "C" fn helper_sub(lhs: JITValue, rhs: JITValue) -> JITValue {
 }
 
 #[unsafe(no_mangle)]
-extern "C" fn helper_call<'jit, 'vm>(
-    vm: *const VM<'jit>,
-    env: *const Env<'jit, 'vm>,
-    func_ptr: *const (),
-    arg: JITValue,
-) -> JITValue {
-    let func: JITFunc = unsafe { std::mem::transmute(func_ptr) };
-    todo!();
-    unsafe { func(vm, env) }
+extern "C" fn helper_eq(lhs: JITValue, rhs: JITValue) -> JITValue {
+    use ValueTag::*;
+    match (lhs.tag, rhs.tag) {
+        (Int, Int) => JITValue {
+            tag: Bool,
+            data: JITValueData {
+                bool: unsafe { lhs.data.int == rhs.data.int }
+            },
+        },
+        _ => todo!(
+            "Equation not implemented for {:?} and {:?}",
+            lhs.tag,
+            rhs.tag
+        ),
+    }
 }
 
 #[unsafe(no_mangle)]
-extern "C" fn helper_lookup<'jit, 'vm>(sym: usize, env: *const Env<'jit, 'vm>) -> JITValue {
+extern "C" fn helper_or(lhs: JITValue, rhs: JITValue) -> JITValue {
+    use ValueTag::*;
+    match (lhs.tag, rhs.tag) {
+        (Bool, Bool) => JITValue {
+            tag: Bool,
+            data: JITValueData {
+                bool: unsafe { lhs.data.bool || rhs.data.bool },
+            },
+        },
+        _ => todo!(
+            "Substruction not implemented for {:?} and {:?}",
+            lhs.tag,
+            rhs.tag
+        ),
+    }
+}
+
+#[unsafe(no_mangle)]
+extern "C" fn helper_call<'jit, 'vm>(
+    func: JITValue,
+    arg: JITValue,
+    vm: *const VM<'jit>,
+) -> JITValue {
+    use ValueTag::*;
+    match func.tag {
+        Function => {
+            let func: Value = func.into();
+            func.call(unsafe { vm.as_ref() }.unwrap(), vec![arg.into()]).unwrap().into()
+        }
+        _ => todo!(),
+    }
+}
+
+#[unsafe(no_mangle)]
+extern "C" fn helper_lookup<'jit, 'vm>(sym: usize, env: *const LetEnv<'jit, 'vm>) -> JITValue {
     let env = unsafe { env.as_ref() }.unwrap();
     let val = env.lookup(sym);
+    dbg!(val.as_ref().unwrap().typename());
     val.unwrap().into()
 }
+
+#[unsafe(no_mangle)]
+extern "C" fn helper_force<'jit, 'vm>(thunk: JITValue, vm: *const VM<'jit>) -> JITValue {
+    let mut val = Value::from(thunk);
+    val.force(unsafe { vm.as_ref() }.unwrap()).unwrap();
+    val.into()
+}
diff --git a/src/jit/mod.rs b/src/jit/mod.rs
index 8fdf63d..4a1a000 100644
--- a/src/jit/mod.rs
+++ b/src/jit/mod.rs
@@ -1,18 +1,19 @@
 use std::rc::Rc;
 
 use inkwell::OptimizationLevel;
+use inkwell::basic_block::BasicBlock;
 use inkwell::builder::Builder;
 use inkwell::context::Context;
 use inkwell::execution_engine::{ExecutionEngine, JitFunction};
 use inkwell::module::Module;
-use inkwell::values::{BasicValueEnum, PointerValue};
+use inkwell::values::{BasicValueEnum, FunctionValue, PointerValue};
 
 use crate::bytecode::{Func, OpCode, UnOp};
 use crate::error::*;
 use crate::stack::Stack;
 use crate::ty::common::Const;
 use crate::ty::internal::{Thunk, Value};
-use crate::vm::{Env, VM};
+use crate::vm::{LetEnv, VM};
 
 mod helpers;
 
@@ -48,17 +49,19 @@ pub struct JITValue {
 pub union JITValueData {
     int: i64,
     float: f64,
-    boolean: bool,
+    bool: bool,
     ptr: *const (),
 }
 
-impl<'jit: 'vm, 'vm> Into<Value<'jit, 'vm>> for JITValue {
-    fn into(self) -> Value<'jit, 'vm> {
+impl<'jit: 'vm, 'vm> From<JITValue> for Value<'jit, 'vm> {
+    fn from(value: JITValue) -> Self {
         use ValueTag::*;
-        match self.tag {
-            Int => Value::Const(Const::Int(unsafe { self.data.int })),
+        match value.tag {
+            Int => Value::Const(Const::Int(unsafe { value.data.int })),
             Null => Value::Const(Const::Null),
-            _ => todo!("not implemented for {:?}", self.tag),
+            Function => Value::Func(unsafe { Rc::from_raw(value.data.ptr as *const _) }),
+            Thunk => Value::Thunk(unsafe { Rc::from_raw(value.data.ptr as *const _) }),
+            _ => todo!("not implemented for {:?}", value.tag),
         }
     }
 }
@@ -70,13 +73,25 @@ impl From<Value<'_, '_>> for JITValue {
                 tag: ValueTag::Int,
                 data: JITValueData { int },
             },
+            Value::Func(func) => JITValue {
+                tag: ValueTag::Function,
+                data: JITValueData {
+                    ptr: Rc::into_raw(func) as *const _ 
+                }
+            },
+            Value::Thunk(thunk) => JITValue {
+                tag: ValueTag::Thunk,
+                data: JITValueData {
+                    ptr: Rc::into_raw(thunk) as *const _ 
+                }
+            },
             _ => todo!(),
         }
     }
 }
 
 pub type JITFunc<'jit, 'vm> =
-    unsafe extern "C" fn(*const VM<'jit>, *const Env<'jit, 'vm>) -> JITValue;
+    unsafe extern "C" fn(*const VM<'jit>, *const LetEnv<'jit, 'vm>) -> JITValue;
 
 pub struct JITContext<'ctx> {
     context: &'ctx Context,
@@ -125,17 +140,25 @@ impl<'vm, 'ctx: 'vm> JITContext<'ctx> {
         let func_ = self
             .module
             .add_function("nixjit_function", self.helpers.func_type, None);
-        let entry = self.context.append_basic_block(func_, "entry");
-        self.builder.position_at_end(entry);
         let env = func_.get_nth_param(1).unwrap().into_pointer_value();
-        while let Some(opcode) = iter.next() {
-            self.single_op(opcode, vm, env, &mut stack)?;
-        }
+        let entry = self.context.append_basic_block(func_, "entry");
+        self.build_expr(
+            &mut iter,
+            vm,
+            env,
+            &mut stack,
+            func_,
+            entry,
+            func.opcodes.len(),
+        )?;
+
         assert_eq!(stack.len(), 1);
         let value = stack.pop();
+        let exit = self.context.append_basic_block(func_, "exit");
+        self.builder.build_unconditional_branch(exit)?;
+        self.builder.position_at_end(exit);
         self.builder.build_return(Some(&value))?;
-        if func_.verify(false) {
-            func_.print_to_stderr();
+        if func_.verify(true) {
             unsafe {
                 let name = func_.get_name().to_str().unwrap();
                 let addr = self.execution_engine.get_function(name).unwrap();
@@ -146,13 +169,82 @@ impl<'vm, 'ctx: 'vm> JITContext<'ctx> {
         }
     }
 
+    fn build_expr<const CAP: usize>(
+        &self,
+        iter: &mut impl Iterator<Item = OpCode>,
+        vm: &'vm VM<'_>,
+        env: PointerValue<'ctx>,
+        stack: &mut Stack<BasicValueEnum<'ctx>, CAP>,
+        func: FunctionValue<'ctx>,
+        bb: BasicBlock<'ctx>,
+        mut length: usize,
+    ) -> Result<usize> {
+        self.builder.position_at_end(bb);
+        while length > 1 {
+            let opcode = iter.next().unwrap();
+            let br = self.single_op(opcode, vm, env, stack)?;
+            length -= 1;
+            if br > 0 {
+                let consq = self.context.append_basic_block(func, "consq");
+                let alter = self.context.append_basic_block(func, "alter");
+                let cont = self.context.append_basic_block(func, "cont");
+                let cond = self
+                    .builder
+                    .build_alloca(self.helpers.value_type, "cond_alloca")?;
+                let result = self
+                    .builder
+                    .build_alloca(self.helpers.value_type, "result_alloca")?;
+                self.builder.build_store(cond, stack.pop())?;
+                self.builder.build_conditional_branch(
+                    self.builder
+                        .build_load(
+                            self.context.bool_type(),
+                            self.builder.build_struct_gep(
+                                self.helpers.value_type,
+                                cond,
+                                1,
+                                "gep_cond",
+                            )?,
+                            "load_cond",
+                        )?
+                        .into_int_value(),
+                    consq,
+                    alter,
+                )?;
+
+                length -= br;
+                let br = self.build_expr(iter, vm, env, stack, func, consq, br)?;
+                self.builder.build_store(result, stack.pop())?;
+                self.builder.build_unconditional_branch(cont)?;
+
+                length -= br;
+                self.build_expr(iter, vm, env, stack, func, alter, br)?;
+                self.builder.build_store(result, stack.pop())?;
+                self.builder.build_unconditional_branch(cont)?;
+
+                self.builder.position_at_end(cont);
+                stack.push(self.builder.build_load(
+                    self.helpers.value_type,
+                    result,
+                    "load_result",
+                )?)?;
+            }
+        }
+        if length > 0 {
+            self.single_op(iter.next().unwrap(), vm, env, stack)
+        } else {
+            Ok(0)
+        }
+    }
+
+    #[inline(always)]
     fn single_op<const CAP: usize>(
         &self,
         opcode: OpCode,
         vm: &'vm VM<'_>,
         env: PointerValue<'ctx>,
         stack: &mut Stack<BasicValueEnum<'ctx>, CAP>,
-    ) -> Result<()> {
+    ) -> Result<usize> {
         match opcode {
             OpCode::Const { idx } => {
                 use Const::*;
@@ -186,54 +278,14 @@ impl<'vm, 'ctx: 'vm> JITContext<'ctx> {
                         .try_as_basic_value()
                         .left()
                         .unwrap(),
-                    _ => todo!(),
+                    Not => self
+                        .builder
+                        .build_direct_call(self.helpers.not, &[rhs.into(), env.into()], "call_neg")?
+                        .try_as_basic_value()
+                        .left()
+                        .unwrap(),
                 })?
             }
-            OpCode::Func { idx } => {
-                let func = vm.get_func(idx);
-                let jit_func_ptr = self.compile_function(func, vm)?;
-                let jit_value = self
-                    .helpers
-                    .value_type
-                    .const_named_struct(&[
-                        self.helpers
-                            .int_type
-                            .const_int(ValueTag::Function as _, false)
-                            .into(),
-                        self.helpers
-                            .ptr_int_type
-                            .const_int(unsafe { jit_func_ptr.as_raw() } as _, false)
-                            .into(),
-                    ])
-                    .into();
-                stack.push(jit_value)?;
-            }
-            OpCode::Call { arity } => {
-                // Assuming arity is 1 for the test case
-                assert_eq!(arity, 1);
-                let arg = stack.pop();
-                let func_value = stack.pop();
-                let func_ptr = self
-                    .builder
-                    .build_extract_value(func_value.into_struct_value(), 1, "func_ptr")?
-                    .into_pointer_value();
-                let result = self
-                    .builder
-                    .build_direct_call(
-                        self.helpers.call,
-                        &[
-                            self.new_ptr(vm).into(),
-                            env.into(),
-                            func_ptr.into(),
-                            arg.into(),
-                        ],
-                        "call_func",
-                    )?
-                    .try_as_basic_value()
-                    .left()
-                    .unwrap();
-                stack.push(result)?;
-            }
             OpCode::BinOp { op } => {
                 use crate::bytecode::BinOp;
                 let rhs = stack.pop();
@@ -269,9 +321,22 @@ impl<'vm, 'ctx: 'vm> JITContext<'ctx> {
                         let result = self
                             .builder
                             .build_direct_call(
-                                self.helpers.add,
+                                self.helpers.eq,
                                 &[lhs.into(), rhs.into()],
-                                "call_add",
+                                "call_eq",
+                            )?
+                            .try_as_basic_value()
+                            .left()
+                            .unwrap();
+                        stack.push(result)?;
+                    }
+                    BinOp::Or => {
+                        let result = self
+                            .builder
+                            .build_direct_call(
+                                self.helpers.or,
+                                &[lhs.into(), rhs.into()],
+                                "call_or",
                             )?
                             .try_as_basic_value()
                             .left()
@@ -299,8 +364,29 @@ impl<'vm, 'ctx: 'vm> JITContext<'ctx> {
                     .left()
                     .unwrap(),
             )?,
+            OpCode::Call { arity } => {
+                // TODO:
+                assert_eq!(arity, 1);
+                let mut args = Vec::with_capacity(arity);
+                for _ in 0..arity {
+                    args.insert(0, stack.pop());
+                }
+                let func = self.builder
+                    .build_direct_call(self.helpers.force, &[stack.pop().into(), self.new_ptr(vm).into()], "force")?
+                    .try_as_basic_value()
+                    .left()
+                    .unwrap();
+                let ret = self.builder
+                    .build_direct_call(self.helpers.call, &[func.into(), args[0].into(), self.new_ptr(vm).into()], "call")?
+                    .try_as_basic_value()
+                    .left()
+                    .unwrap();
+                stack.push(ret)?;
+            }
+            OpCode::JmpIfFalse { step } => return Ok(step),
+            OpCode::Jmp { step } => return Ok(step),
             _ => todo!("{opcode:?} not implemented"),
         }
-        Ok(())
+        Ok(0)
     }
 }
diff --git a/src/stack.rs b/src/stack.rs
index 675321b..d738a8f 100644
--- a/src/stack.rs
+++ b/src/stack.rs
@@ -45,8 +45,8 @@ impl<T, const CAP: usize> Stack<T, CAP> {
     }
 
     pub fn pop(&mut self) -> T {
+        let item = self.items.get_mut(self.top - 1).unwrap();
         self.top -= 1;
-        let item = self.items.get_mut(self.top).unwrap();
 
         // SAFETY: `item` at `self.top` was previously written and is initialized.
         // We replace it with `MaybeUninit::uninit()` and then `assume_init`
diff --git a/src/ty/internal/attrset.rs b/src/ty/internal/attrset.rs
index 9925727..0687f01 100644
--- a/src/ty/internal/attrset.rs
+++ b/src/ty/internal/attrset.rs
@@ -4,24 +4,24 @@ use derive_more::Constructor;
 use itertools::Itertools;
 
 use crate::error::Result;
-use crate::vm::{Env, VM};
+use crate::vm::{LetEnv, VM};
 
 use super::super::public as p;
 use super::Value;
 
 #[repr(C)]
-#[derive(Debug, Constructor, Clone, PartialEq)]
+#[derive(Debug, Default, Constructor, Clone, PartialEq)]
 pub struct AttrSet<'jit: 'vm, 'vm> {
     data: HashMap<usize, Value<'jit, 'vm>>,
 }
 
-impl<'jit: 'vm, 'vm> AttrSet<'jit, 'vm> {
-    pub fn empty() -> Self {
-        AttrSet {
-            data: HashMap::new(),
-        }
+impl<'jit, 'vm> From<HashMap<usize, Value<'jit, 'vm>>> for AttrSet<'jit, 'vm> {
+    fn from(data: HashMap<usize, Value<'jit, 'vm>>) -> Self {
+        Self { data }
     }
+}
 
+impl<'jit: 'vm, 'vm> AttrSet<'jit, 'vm> {
     pub fn with_capacity(cap: usize) -> Self {
         AttrSet {
             data: HashMap::with_capacity(cap),
@@ -47,7 +47,7 @@ impl<'jit: 'vm, 'vm> AttrSet<'jit, 'vm> {
         self.data.get(&sym).is_some()
     }
 
-    pub fn capture(&mut self, env: &Env<'jit, 'vm>) {
+    pub fn capture(&mut self, env: &LetEnv<'jit, 'vm>) {
         self.data.iter().for_each(|(_, v)| match v.clone() {
             Value::Thunk(ref thunk) => {
                 thunk.capture(env.clone());
diff --git a/src/ty/internal/func.rs b/src/ty/internal/func.rs
index ac1ec70..a651ec1 100644
--- a/src/ty/internal/func.rs
+++ b/src/ty/internal/func.rs
@@ -9,7 +9,7 @@ use crate::error::Result;
 use crate::ir;
 use crate::jit::JITFunc;
 use crate::ty::internal::{Thunk, Value};
-use crate::vm::{Env, VM};
+use crate::vm::{LetEnv, VM};
 
 #[derive(Debug, Clone)]
 pub enum Param {
@@ -44,7 +44,7 @@ impl From<ir::Param> for Param {
 #[derive(Debug, Clone, Constructor)]
 pub struct Func<'jit: 'vm, 'vm> {
     pub func: &'vm BFunc,
-    pub env: Env<'jit, 'vm>,
+    pub env: LetEnv<'jit, 'vm>,
     pub compiled: OnceCell<JitFunction<'jit, JITFunc<'jit, 'vm>>>,
     pub count: Cell<usize>,
 }
@@ -54,7 +54,7 @@ impl<'vm, 'jit: 'vm> Func<'jit, 'vm> {
         use Param::*;
 
         let env = match self.func.param.clone() {
-            Ident(ident) => self.env.clone().enter([(ident.into(), arg)].into_iter()),
+            Ident(ident) => self.env.clone().enter_let([(ident.into(), arg)].into_iter()),
             Formals {
                 formals,
                 ellipsis,
@@ -85,7 +85,7 @@ impl<'vm, 'jit: 'vm> Func<'jit, 'vm> {
                 if let Some(alias) = alias {
                     new.push((alias.clone().into(), Value::AttrSet(arg)));
                 }
-                self.env.clone().enter(new.into_iter())
+                self.env.clone().enter_let(new.into_iter())
             }
         };
 
@@ -93,7 +93,7 @@ impl<'vm, 'jit: 'vm> Func<'jit, 'vm> {
         self.count.replace(count + 1);
         if count >= 1 {
             let compiled = self.compiled.get_or_init(|| vm.compile_func(self.func));
-            let ret = unsafe { compiled.call(vm as *const VM, &env as *const Env) };
+            let ret = unsafe { compiled.call(vm as *const VM, &env as *const LetEnv) };
             return Ok(ret.into());
         }
         vm.eval(self.func.opcodes.iter().copied(), env)
diff --git a/src/ty/internal/mod.rs b/src/ty/internal/mod.rs
index 10b3826..2c6ff42 100644
--- a/src/ty/internal/mod.rs
+++ b/src/ty/internal/mod.rs
@@ -11,7 +11,7 @@ use super::public as p;
 
 use crate::bytecode::OpCodes;
 use crate::error::*;
-use crate::vm::{Env, VM};
+use crate::vm::{LetEnv, VM};
 
 mod attrset;
 mod func;
@@ -157,7 +157,11 @@ impl<'jit, 'vm> Value<'jit, 'vm> {
     pub fn typename(&self) -> &'static str {
         use Value::*;
         match self {
-            Const(_) => unreachable!(),
+            Const(self::Const::Int(_)) => "int",
+            Const(self::Const::Float(_)) => "float",
+            Const(self::Const::Bool(_)) => "bool",
+            Const(self::Const::String(_)) => "string",
+            Const(self::Const::Null) => "null",
             Thunk(_) => "thunk",
             ThunkRef(_) => "thunk",
             AttrSet(_) => "set",
@@ -481,7 +485,7 @@ pub struct Thunk<'jit, 'vm> {
 
 #[derive(Debug, IsVariant, Unwrap, Clone)]
 pub enum _Thunk<'jit, 'vm> {
-    Code(&'vm OpCodes, OnceCell<Env<'jit, 'vm>>),
+    Code(&'vm OpCodes, OnceCell<LetEnv<'jit, 'vm>>),
     SuspendedFrom(*const Thunk<'jit, 'vm>),
     Value(Value<'jit, 'vm>),
 }
@@ -493,7 +497,7 @@ impl<'jit, 'vm> Thunk<'jit, 'vm> {
         }
     }
 
-    pub fn capture(&self, env: Env<'jit, 'vm>) {
+    pub fn capture(&self, env: LetEnv<'jit, 'vm>) {
         if let _Thunk::Code(_, envcell) = &*self.thunk.borrow() {
             envcell.get_or_init(|| env);
         }
diff --git a/src/vm/env.rs b/src/vm/env.rs
index b7b5c65..af24084 100644
--- a/src/vm/env.rs
+++ b/src/vm/env.rs
@@ -4,14 +4,20 @@ use std::rc::Rc;
 use crate::ty::internal::{AttrSet, Value};
 
 #[derive(Debug, Default, Clone)]
-pub struct Env<'jit, 'vm> {
-    pub map: Rc<HashMap<usize, Value<'jit, 'vm>>>,
-    pub last: Option<Rc<Env<'jit, 'vm>>>,
+pub struct LetEnv<'jit, 'vm> {
+    map: Rc<HashMap<usize, Value<'jit, 'vm>>>,
+    last: Option<Rc<LetEnv<'jit, 'vm>>>,
 }
 
-impl<'jit, 'vm> Env<'jit, 'vm> {
-    pub fn empty() -> Self {
-        Env::default()
+#[derive(Debug, Default, Clone)]
+pub struct WithEnv<'jit, 'vm> {
+    map: Rc<AttrSet<'jit, 'vm>>,
+    last: Option<Rc<WithEnv<'jit, 'vm>>>,
+}
+
+impl<'jit, 'vm> LetEnv<'jit, 'vm> {
+    pub fn new(map: Rc<HashMap<usize, Value<'jit, 'vm>>>) -> Self {
+        Self { map, last: None }
     }
 
     pub fn lookup(&self, symbol: usize) -> Option<Value<'jit, 'vm>> {
@@ -21,46 +27,63 @@ impl<'jit, 'vm> Env<'jit, 'vm> {
         self.last.as_ref().map(|env| env.lookup(symbol)).flatten()
     }
 
-    pub fn insert(&mut self, symbol: usize, value: Value<'jit, 'vm>) {
-        Rc::make_mut(&mut self.map).insert(symbol, value);
-    }
-
-    pub fn enter(self, new: impl Iterator<Item = (usize, Value<'jit, 'vm>)>) -> Self {
+    pub fn enter_let(self, new: impl Iterator<Item = (usize, Value<'jit, 'vm>)>) -> Self {
         let map = Rc::new(new.collect());
-        let last = Some(
-            Env {
-                last: self.last,
-                map: self.map,
-            }
-            .into(),
-        );
-        Env { last, map }
+        let last = Some(self.into());
+        LetEnv { last, map }
     }
 
     pub fn enter_with(self, new: Rc<AttrSet<'jit, 'vm>>) -> Self {
-        let map = Rc::new(
-            new.as_inner()
-                .iter()
-                .map(|(&k, v)| {
-                    (
-                        k,
-                        if let Value::Builtins(weak) = v {
-                            Value::AttrSet(weak.upgrade().unwrap())
-                        } else {
-                            v.clone()
-                        },
-                    )
-                })
-                .collect(),
-        );
-        let last = Some(
-            Env {
-                last: self.last.clone(),
-                map: self.map.clone(),
-            }
-            .into(),
-        );
-        Env { last, map }
+        let map = new
+            .as_inner()
+            .iter()
+            .map(|(&k, v)| {
+                (
+                    k,
+                    if let Value::Builtins(weak) = v {
+                        Value::AttrSet(weak.upgrade().unwrap())
+                    } else {
+                        v.clone()
+                    },
+                )
+            })
+            .collect::<HashMap<_, _>>()
+            .into();
+        let last = Some(self.into());
+        LetEnv { last, map }
+    }
+
+    pub fn leave(self) -> Self {
+        self.last.unwrap().as_ref().clone()
+    }
+}
+
+impl<'jit, 'vm> WithEnv<'jit, 'vm> {
+    pub fn lookup(&self, symbol: usize) -> Option<Value<'jit, 'vm>> {
+        if let Some(val) = self.map.select(symbol) {
+            return Some(val);
+        }
+        self.last.as_ref().map(|env| env.lookup(symbol)).flatten()
+    }
+
+    pub fn enter_with(self, new: Rc<AttrSet<'jit, 'vm>>) -> Self {
+        let map = Rc::new(new
+            .as_inner()
+            .iter()
+            .map(|(&k, v)| {
+                (
+                    k,
+                    if let Value::Builtins(weak) = v {
+                        Value::AttrSet(weak.upgrade().unwrap())
+                    } else {
+                        v.clone()
+                    },
+                )
+            })
+            .collect::<HashMap<_, _>>()
+            .into());
+        let last = Some(self.into());
+        WithEnv { last, map }
     }
 
     pub fn leave(self) -> Self {
diff --git a/src/vm/mod.rs b/src/vm/mod.rs
index c1f73f9..2fab1e0 100644
--- a/src/vm/mod.rs
+++ b/src/vm/mod.rs
@@ -13,7 +13,7 @@ use crate::ty::public::{self as p, Symbol};
 
 use derive_more::Constructor;
 use ecow::EcoString;
-pub use env::Env;
+pub use env::LetEnv;
 
 mod env;
 
@@ -82,7 +82,7 @@ impl<'vm, 'jit: 'vm> VM<'jit> {
     pub fn eval(
         &'vm self,
         opcodes: impl Iterator<Item = OpCode>,
-        mut env: Env<'jit, 'vm>,
+        mut env: LetEnv<'jit, 'vm>,
     ) -> Result<Value<'jit, 'vm>> {
         let mut stack = Stack::<_, STACK_SIZE>::new();
         let mut iter = opcodes.into_iter();
@@ -103,7 +103,7 @@ impl<'vm, 'jit: 'vm> VM<'jit> {
         &'vm self,
         opcode: OpCode,
         stack: &'s mut Stack<Value<'jit, 'vm>, CAP>,
-        env: &mut Env<'jit, 'vm>,
+        env: &mut LetEnv<'jit, 'vm>,
     ) -> Result<usize> {
         match opcode {
             OpCode::Illegal => panic!("illegal opcode"),
@@ -121,11 +121,6 @@ impl<'vm, 'jit: 'vm> VM<'jit> {
                 stack.tos_mut()?.force(self)?;
             }
             OpCode::Jmp { step } => return Ok(step),
-            OpCode::JmpIfTrue { step } => {
-                if let Value::Const(Const::Bool(true)) = stack.pop() {
-                    return Ok(step);
-                }
-            }
             OpCode::JmpIfFalse { step } => {
                 if let Value::Const(Const::Bool(false)) = stack.pop() {
                     return Ok(step);
@@ -193,7 +188,7 @@ impl<'vm, 'jit: 'vm> VM<'jit> {
                 stack.push(Value::AttrSet(AttrSet::with_capacity(cap).into()))?;
             }
             OpCode::FinalizeRec => {
-                let env = env.clone().enter(
+                let env = env.clone().enter_let(
                     stack
                         .tos()?
                         .clone()