diff --git a/lang/README.md b/lang/README.md
index f57453a..50c0c55 100644
--- a/lang/README.md
+++ b/lang/README.md
@@ -212,7 +212,7 @@ use_foo := fn(foo: Foo, str: ^u8): void {
 Bar := struct {a: ?^uint, b: uint}
 new_bar := fn(a: ?^uint): ?Bar return .(a, 1)
 
-decide := fn(): bool return true
+decide := fn(): bool return !false
 ```
 
 #### structs
diff --git a/lang/src/lexer.rs b/lang/src/lexer.rs
index c4bd805..2cacd5a 100644
--- a/lang/src/lexer.rs
+++ b/lang/src/lexer.rs
@@ -263,6 +263,7 @@ impl TokenKind {
         match self {
             Self::Sub if float => (-f64::from_bits(value as _)).to_bits() as _,
             Self::Sub => value.wrapping_neg(),
+            Self::Not => (value == 0) as _,
             Self::Float if float => value,
             Self::Float => (value as f64).to_bits() as _,
             Self::Number => {
diff --git a/lang/src/parser.rs b/lang/src/parser.rs
index f65ad9f..7d8ef97 100644
--- a/lang/src/parser.rs
+++ b/lang/src/parser.rs
@@ -459,7 +459,7 @@ impl<'a, 'b> Parser<'a, 'b> {
                     pos
                 },
             },
-            T::Band | T::Mul | T::Xor | T::Sub | T::Que => E::UnOp {
+            T::Band | T::Mul | T::Xor | T::Sub | T::Que | T::Not => E::UnOp {
                 pos,
                 op: token.kind,
                 val: {
diff --git a/lang/src/son.rs b/lang/src/son.rs
index 13f538f..52ba57a 100644
--- a/lang/src/son.rs
+++ b/lang/src/son.rs
@@ -2029,12 +2029,6 @@ struct Variable {
 
 impl Variable {
     fn new(id: Ident, ty: ty::Id, ptr: bool, value: Nid, nodes: &mut Nodes) -> Self {
-        if value == NEVER {
-            if ty == ty::Id::NEVER {
-                panic!();
-            }
-        }
-
         Self { id, ty, ptr, value: StrongRef::new(value, nodes) }
     }
 
@@ -2813,6 +2807,21 @@ impl<'a> Codegen<'a> {
                     Value::NEVER
                 }
             }
+            Expr::UnOp { pos, op: op @ TokenKind::Not, val } => {
+                let val =
+                    self.expr_ctx(val, Ctx::default().with_ty(ctx.ty.unwrap_or(ty::Id::INT)))?;
+                if val.ty == ty::Id::BOOL {
+                    Some(self.ci.nodes.new_node_lit(
+                        val.ty,
+                        Kind::UnOp { op },
+                        [VOID, val.id],
+                        self.tys,
+                    ))
+                } else {
+                    self.report(pos, fa!("cant logically negate '{}'", self.ty_display(val.ty)));
+                    Value::NEVER
+                }
+            }
             Expr::BinOp { left, op: TokenKind::Decl, right, pos } => {
                 let mut right = self.expr(right)?;
 
diff --git a/lang/src/son/hbvm.rs b/lang/src/son/hbvm.rs
index 4eef68b..5ab76e1 100644
--- a/lang/src/son/hbvm.rs
+++ b/lang/src/son/hbvm.rs
@@ -568,7 +568,10 @@ impl TokenKind {
         Some(match self {
             Self::Sub => instrs::neg,
             Self::Float if dst.is_float() && src.is_integer() => {
-                debug_assert_eq!(dst.simple_size(), src.simple_size());
+                debug_assert_matches!(
+                    (dst.simple_size(), src.simple_size()),
+                    (Some(4 | 8), Some(8))
+                );
                 [instrs::itf32, instrs::itf64][src_idx]
             }
             Self::Number if src.is_float() && dst.is_integer() => {