diff --git a/src/comptime.rs b/src/comptime.rs
index 1a07284..e6522ef 100644
--- a/src/comptime.rs
+++ b/src/comptime.rs
@@ -1499,12 +1499,15 @@ pub mod bigsint {
     }
 }
 
-use std::ops::{Add, BitAnd, BitOr, BitXor, Not};
+use std::{
+    cmp::Ordering,
+    ops::{Add, BitAnd, BitOr, BitXor, Not},
+};
 
-use num_bigint::{BigInt, Sign};
+use num_bigint::{BigInt, BigUint, Sign};
 use num_traits::cast::ToPrimitive;
 
-use crate::ast::IntegralType;
+use crate::ast::{FloatingType, IntegralType};
 
 #[derive(Debug, thiserror::Error)]
 pub enum Error {
@@ -1516,10 +1519,13 @@ pub enum Error {
     ShiftTooLarge,
     #[error("Cannot negate unsigned integer")]
     UnsignedNegation,
+    #[error("Incomparable floats.")]
+    FloatingCmp,
 }
 
 pub type Result<T> = core::result::Result<T, Error>;
 
+#[derive(Debug, PartialEq, Eq)]
 pub enum ComptimeInt {
     Native { bits: u128, ty: IntegralType },
     BigInt { bits: BigInt, ty: IntegralType },
@@ -1710,6 +1716,19 @@ impl ComptimeInt {
             }
         }
     }
+    pub fn cmp(self, other: Self) -> Result<Ordering> {
+        let (a, b) = self.coalesce(other)?;
+        let ord = match (a, b) {
+            (ComptimeInt::Native { bits: a, .. }, ComptimeInt::Native { bits: b, .. }) => a.cmp(&b),
+            (ComptimeInt::BigInt { bits: a, .. }, ComptimeInt::BigInt { bits: b, .. }) => a.cmp(&b),
+            (ComptimeInt::Comptime(a), ComptimeInt::Comptime(b)) => a.cmp(&b),
+            _ => {
+                unreachable!()
+            }
+        };
+
+        Ok(ord)
+    }
 
     pub fn shl(self, other: Self) -> Result<Self> {
         use core::ops::Shl;
@@ -1884,6 +1903,7 @@ impl ComptimeInt {
     }
 }
 
+#[derive(Debug, PartialEq)]
 pub enum ComptimeFloat {
     Binary32(f32),
     Binary64(f64),
@@ -1931,6 +1951,17 @@ impl ComptimeFloat {
             ComptimeFloat::Binary64(a) => Ok(Self::Binary64(-a)),
         }
     }
+    pub fn cmp(self, other: Self) -> Result<Ordering> {
+        let ord = match (self, other) {
+            (ComptimeFloat::Binary32(a), ComptimeFloat::Binary32(b)) => a.partial_cmp(&b),
+            (ComptimeFloat::Binary64(a), ComptimeFloat::Binary64(b)) => a.partial_cmp(&b),
+            _ => {
+                return Err(Error::IncompatibleTypes);
+            }
+        };
+
+        ord.ok_or(Error::FloatingCmp)
+    }
 }
 
 pub enum ComptimeNumber {
@@ -1939,6 +1970,41 @@ pub enum ComptimeNumber {
     Floating(ComptimeFloat),
 }
 
+impl From<bool> for ComptimeNumber {
+    fn from(value: bool) -> Self {
+        Self::Bool(value)
+    }
+}
+
+impl From<f32> for ComptimeNumber {
+    fn from(value: f32) -> Self {
+        Self::Floating(ComptimeFloat::Binary32(value))
+    }
+}
+
+impl From<f64> for ComptimeNumber {
+    fn from(value: f64) -> Self {
+        Self::Floating(ComptimeFloat::Binary64(value))
+    }
+}
+
+impl From<BigInt> for ComptimeNumber {
+    fn from(value: BigInt) -> Self {
+        Self::Integral(ComptimeInt::Comptime(value))
+    }
+}
+
+impl From<(BigInt, IntegralType)> for ComptimeNumber {
+    fn from((bits, ty): (BigInt, IntegralType)) -> Self {
+        Self::Integral(ComptimeInt::BigInt { bits, ty })
+    }
+}
+impl From<(u128, IntegralType)> for ComptimeNumber {
+    fn from((bits, ty): (u128, IntegralType)) -> Self {
+        Self::Integral(ComptimeInt::Native { bits, ty })
+    }
+}
+
 impl ComptimeNumber {
     pub fn add(self, other: Self) -> Result<Self> {
         match (self, other) {
@@ -2076,4 +2142,125 @@ impl ComptimeNumber {
             _ => Err(Error::IncompatibleTypes),
         }
     }
+    pub fn or(self, other: Self) -> Result<Self> {
+        match (self, other) {
+            // (ComptimeNumber::Integral(a), ComptimeNumber::Integral(b)) => {
+            //     Ok(Self::Integral(a.shr(b)?))
+            // }
+            // (ComptimeNumber::Floating(a), ComptimeNumber::Floating(b)) => {
+            //     Ok(Self::Floating(a.bitxor(b)?))
+            // }
+            (ComptimeNumber::Bool(a), ComptimeNumber::Bool(b)) => Ok(Self::Bool(a || b)),
+            _ => Err(Error::IncompatibleTypes),
+        }
+    }
+    pub fn and(self, other: Self) -> Result<Self> {
+        match (self, other) {
+            // (ComptimeNumber::Integral(a), ComptimeNumber::Integral(b)) => {
+            //     Ok(Self::Integral(a.shr(b)?))
+            // }
+            // (ComptimeNumber::Floating(a), ComptimeNumber::Floating(b)) => {
+            //     Ok(Self::Floating(a.bitxor(b)?))
+            // }
+            (ComptimeNumber::Bool(a), ComptimeNumber::Bool(b)) => Ok(Self::Bool(a && b)),
+            _ => Err(Error::IncompatibleTypes),
+        }
+    }
+    pub fn eq(self, other: Self) -> Result<Self> {
+        match (self, other) {
+            (ComptimeNumber::Integral(a), ComptimeNumber::Integral(b)) => Ok(Self::Bool(a == b)),
+            (ComptimeNumber::Floating(a), ComptimeNumber::Floating(b)) => Ok(Self::Bool(a == b)),
+            (ComptimeNumber::Bool(a), ComptimeNumber::Bool(b)) => Ok(Self::Bool(a == b)),
+            _ => Err(Error::IncompatibleTypes),
+        }
+    }
+
+    pub fn cmp(self, other: Self) -> Result<Ordering> {
+        let ord = match (self, other) {
+            (ComptimeNumber::Integral(a), ComptimeNumber::Integral(b)) => a.cmp(b)?,
+            (ComptimeNumber::Floating(a), ComptimeNumber::Floating(b)) => a.cmp(b)?,
+            (ComptimeNumber::Bool(a), ComptimeNumber::Bool(b)) => a.cmp(&b),
+            _ => {
+                return Err(Error::IncompatibleTypes);
+            }
+        };
+
+        Ok(ord)
+    }
+
+    pub fn lt(self, other: Self) -> Result<Self> {
+        Ok(Self::Bool(self.cmp(other)? == Ordering::Less))
+    }
+
+    pub fn gt(self, other: Self) -> Result<Self> {
+        Ok(Self::Bool(self.cmp(other)? == Ordering::Greater))
+    }
+
+    pub fn ge(self, other: Self) -> Result<Self> {
+        Ok(Self::Bool(self.cmp(other)? != Ordering::Less))
+    }
+
+    pub fn le(self, other: Self) -> Result<Self> {
+        Ok(Self::Bool(self.cmp(other)? != Ordering::Greater))
+    }
+
+    pub fn into_bool(self) -> Result<Self> {
+        match self {
+            ComptimeNumber::Integral(i) => match i {
+                ComptimeInt::Native { bits, .. } => Ok((bits != 0).into()),
+                ComptimeInt::Comptime(bits) | ComptimeInt::BigInt { bits, .. } => {
+                    Ok((bits.sign() != Sign::NoSign).into())
+                }
+            },
+            ComptimeNumber::Floating(ComptimeFloat::Binary32(f)) => Ok((f != 0.0).into()),
+            ComptimeNumber::Floating(ComptimeFloat::Binary64(f)) => Ok((f != 0.0).into()),
+            a => Ok(a),
+        }
+    }
+
+    pub fn into_int(self, ty: IntegralType) -> Result<Self> {
+        match self {
+            ComptimeNumber::Integral(i) => match i {
+                ComptimeInt::Native { bits, .. } => Ok((bits & ty.u128_bitmask(), ty).into()),
+                ComptimeInt::Comptime(bits) | ComptimeInt::BigInt { bits, .. } => {
+                    let max = BigUint::from(2u32).pow((ty.bits - ty.signed as u16) as u32);
+                    let (sign, data) = bits.into_parts();
+                    let data = data.clamp(BigUint::ZERO, max);
+
+                    Ok((BigInt::from_biguint(sign, data), ty).into())
+                }
+            },
+            ComptimeNumber::Bool(b) => Ok((b as u128 & ty.u128_bitmask(), ty).into()),
+            ComptimeNumber::Floating(f) => match f {
+                ComptimeFloat::Binary32(f) => Ok((f as u128 & ty.u128_bitmask(), ty).into()),
+                ComptimeFloat::Binary64(f) => Ok((f as u128 & ty.u128_bitmask(), ty).into()),
+            },
+        }
+    }
+    pub fn into_float(self, ty: FloatingType) -> Result<Self> {
+        let f = match self {
+            ComptimeNumber::Integral(i) => match i {
+                ComptimeInt::Native { bits, .. } => bits as f64,
+                ComptimeInt::Comptime(bits) | ComptimeInt::BigInt { bits, .. } => {
+                    bits.to_f64().unwrap_or(f64::NAN)
+                }
+            },
+            ComptimeNumber::Bool(b) => {
+                if b {
+                    1.0f64
+                } else {
+                    0.0f64
+                }
+            }
+            ComptimeNumber::Floating(f) => match f {
+                ComptimeFloat::Binary32(f) => f as f64,
+                ComptimeFloat::Binary64(f) => f as f64,
+            },
+        };
+
+        match ty {
+            FloatingType::Binary32 => Ok((f as f32).into()),
+            FloatingType::Binary64 => Ok(f.into()),
+        }
+    }
 }
diff --git a/src/parser.rs b/src/parser.rs
index f81583f..6996195 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -1,11 +1,12 @@
 use std::collections::HashMap;
 
 use itertools::Itertools;
+use num_bigint::BigInt;
 
 use crate::{
     ast::{FloatingType, IntegralType, LetOrVar, Node, PrimitiveType, Tag, Type},
     common::NextIf,
-    comptime::bigint::{self, BigInt},
+    comptime::{self, ComptimeNumber},
     error::{AnalysisError, AnalysisErrorTag},
     lexer::{Radix, TokenIterator},
     string_table::{ImmOrIndex, Index, StringTable},
@@ -1546,6 +1547,270 @@ impl Tree {
     }
 }
 
+// simplify tree with compile-time math
+impl Tree {
+    fn is_node_comptime(&self, node: Node) -> bool {
+        match self.nodes.get_node(node) {
+            Tag::Block {
+                statements,
+                trailing_expr,
+            } => statements
+                .iter()
+                .chain(trailing_expr.into_iter())
+                .all(|n| self.is_node_comptime(*n)),
+            Tag::Constant { .. } => true,
+            Tag::ExplicitCast { lhs, typename } => {
+                self.is_node_comptime(*lhs)
+                    && match self.type_of_node(*typename) {
+                        Type::Bool
+                        | Type::ComptimeNumber
+                        | Type::Integer(_)
+                        | Type::Floating(_) => true,
+                        _ => false,
+                    }
+            }
+            Tag::DeclRef(lhs) | Tag::Not { lhs } | Tag::Negate { lhs } => {
+                self.is_node_comptime(*lhs)
+            }
+            Tag::Or { lhs, rhs }
+            | Tag::And { lhs, rhs }
+            | Tag::BitOr { lhs, rhs }
+            | Tag::BitAnd { lhs, rhs }
+            | Tag::BitXOr { lhs, rhs }
+            | Tag::Eq { lhs, rhs }
+            | Tag::NEq { lhs, rhs }
+            | Tag::Lt { lhs, rhs }
+            | Tag::Gt { lhs, rhs }
+            | Tag::Le { lhs, rhs }
+            | Tag::Ge { lhs, rhs }
+            | Tag::Shl { lhs, rhs }
+            | Tag::Shr { lhs, rhs }
+            | Tag::Add { lhs, rhs }
+            | Tag::Sub { lhs, rhs }
+            | Tag::Mul { lhs, rhs }
+            | Tag::Rem { lhs, rhs }
+            | Tag::Div { lhs, rhs } => self.is_node_comptime(*lhs) && self.is_node_comptime(*rhs),
+            _ => false,
+        }
+    }
+
+    fn try_fold_comptime_inner(&mut self, node: Node) {
+        if self.is_node_comptime(node) {
+            self.fold_comptime_inner(node);
+        }
+    }
+
+    fn fold_comptime_inner(&mut self, decl: Node) -> comptime::Result<ComptimeNumber> {
+        //
+        if self.is_node_comptime(decl) {
+            match self.nodes.get_node(decl) {
+                Tag::Constant { bytes, ty } => {
+                    let bytes = match bytes {
+                        ImmOrIndex::U64(v) => &v.to_le_bytes()[..],
+
+                        ImmOrIndex::U32(v) => &v.to_le_bytes()[..],
+                        ImmOrIndex::Index(idx) => self.strings.get_bytes(*idx),
+                    };
+
+                    let number: ComptimeNumber = match ty {
+                        Type::Bool => (bytes[0] != 0).into(),
+                        Type::ComptimeNumber => {
+                            BigInt::from_bytes_le(num_bigint::Sign::Plus, bytes).into()
+                        }
+                        Type::Integer(ty) => {
+                            if bytes.len() > core::mem::size_of::<u128>() {
+                                let bits = BigInt::from_bytes_le(num_bigint::Sign::Plus, bytes);
+                                (bits, *ty).into()
+                            } else {
+                                let mut buf = [0u8; core::mem::size_of::<u128>()];
+                                buf[..bytes.len()].copy_from_slice(bytes);
+                                let bits = u128::from_le_bytes(buf);
+                                (bits, *ty).into()
+                            }
+                        }
+                        Type::Floating(ty) => match ty {
+                            FloatingType::Binary32 => {
+                                (f32::from_le_bytes((&bytes[..4]).try_into().unwrap())).into()
+                            }
+                            FloatingType::Binary64 => {
+                                (f64::from_le_bytes((&bytes[..8]).try_into().unwrap())).into()
+                            }
+                        },
+                        _ => unimplemented!(),
+                    };
+                    return Ok(number);
+                }
+                Tag::Negate { lhs } => {
+                    let lhs = self.fold_comptime_inner(*lhs)?;
+                    return Ok(lhs.neg()?);
+                }
+                Tag::ExplicitCast { lhs, typename } => {
+                    let ty = self.type_of_node(*typename);
+                    let lhs = self.fold_comptime_inner(*lhs)?;
+
+                    return match ty {
+                        Type::Bool => lhs.into_bool(),
+                        Type::Integer(ty) => lhs.into_int(ty),
+                        Type::Floating(ty) => lhs.into_float(ty),
+                        _ => unimplemented!(),
+                    };
+                }
+                Tag::DeclRef(lhs) => {
+                    return self.fold_comptime_inner(*lhs);
+                }
+                Tag::Not { lhs } => {
+                    let lhs = self.fold_comptime_inner(*lhs)?;
+                    return lhs.not();
+                }
+                Tag::Or { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.or(rhs);
+                }
+                Tag::And { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.and(rhs);
+                }
+                Tag::Eq { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.eq(rhs);
+                }
+                Tag::NEq { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.eq(rhs)?.not();
+                }
+                Tag::Lt { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.lt(rhs);
+                }
+                Tag::Gt { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.gt(rhs);
+                }
+                Tag::Le { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.le(rhs);
+                }
+                Tag::Ge { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.ge(rhs);
+                }
+                Tag::BitOr { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.bitor(rhs);
+                }
+                Tag::BitAnd { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.bitand(rhs);
+                }
+                Tag::BitXOr { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.bitxor(rhs);
+                }
+                Tag::Shl { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.shl(rhs);
+                }
+                Tag::Shr { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.shr(rhs);
+                }
+                Tag::Add { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.add(rhs);
+                }
+                Tag::Sub { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.sub(rhs);
+                }
+                Tag::Mul { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.mul(rhs);
+                }
+                Tag::Rem { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.rem(rhs);
+                }
+                Tag::Div { lhs, rhs } => {
+                    let (lhs, rhs) = (*lhs, *rhs);
+                    let lhs = self.fold_comptime_inner(lhs)?;
+                    let rhs = self.fold_comptime_inner(rhs)?;
+
+                    return lhs.div(rhs);
+                }
+                _ => {
+                    unreachable!()
+                }
+            }
+        }
+        todo!()
+    }
+
+    pub fn fold_comptime(&mut self) {
+        for decl in self.global_decls.clone() {
+            match self.nodes.get_node(decl) {
+                Tag::FunctionDecl { body, .. } => {
+                    self.fold_comptime_inner(*body);
+                }
+                Tag::GlobalDecl { assignment, .. } => {
+                    self.fold_comptime_inner(*assignment);
+                }
+                _ => unreachable!(),
+            }
+        }
+    }
+}
+
 impl Tree {
     /// type-checks and inserts appropriate explicit-cast nodes.
     pub fn typecheck(&mut self) {