diff --git a/crates/luaify/src/generate.rs b/crates/luaify/src/generate.rs
index bdf14c2..da0c3ae 100644
--- a/crates/luaify/src/generate.rs
+++ b/crates/luaify/src/generate.rs
@@ -916,7 +916,7 @@ fn generate_pat_typed(f: &mut Formatter, typed: &PatType, cx: PatContext) -> Res
     assert_no_attrs!(typed);
     match *typed.ty {
         Type::Infer(_) => generate_pat(f, &typed.pat, cx),
-        ref ty => syn_error!(ty, "cannot have type"),
+        ref ty => syn_error!(ty, "cannot specify type"),
     }
 }
 
diff --git a/crates/luaify/src/transform.rs b/crates/luaify/src/transform.rs
index 8c6047d..3acd10e 100644
--- a/crates/luaify/src/transform.rs
+++ b/crates/luaify/src/transform.rs
@@ -1,6 +1,4 @@
-use crate::utils::{LuaType, expr_ident, pat_ident, syn_error, wrap_expr_block};
-use quote::format_ident;
-use std::mem;
+use crate::utils::syn_error;
 use syn::{spanned::*, visit_mut::*, *};
 
 pub fn transform(expr: &mut Expr) -> Result<()> {
@@ -27,27 +25,6 @@ impl Visitor {
 }
 
 impl VisitMut for Visitor {
-    fn visit_expr_closure_mut(&mut self, clo: &mut ExprClosure) {
-        match self.transform_expr_closure(clo) {
-            res @ Err(_) => self.result = res,
-            _ => visit_expr_closure_mut(self, clo),
-        }
-    }
-
-    fn visit_item_fn_mut(&mut self, func: &mut ItemFn) {
-        match self.transform_function(func) {
-            res @ Err(_) => self.result = res,
-            _ => visit_item_fn_mut(self, func),
-        }
-    }
-
-    fn visit_expr_mut(&mut self, expr: &mut Expr) {
-        match self.transform_expr(expr) {
-            res @ Err(_) => self.result = res,
-            _ => visit_expr_mut(self, expr),
-        }
-    }
-
     fn visit_expr_unary_mut(&mut self, un: &mut ExprUnary) {
         match self.transform_unary(un) {
             res @ Err(_) => self.result = res,
@@ -64,147 +41,9 @@ impl VisitMut for Visitor {
 }
 
 impl Visitor {
-    fn transform_expr_closure(&mut self, clo: &mut ExprClosure) -> Result<()> {
-        //
-        // transforms a closure expression with input type annotations by removing the annotations
-        // and inserting `as` casts at the start.
-        //
-        // before:
-        //    |a: string, b: number| { ... }
-        // after:
-        //    |a, b| { a as string; b as number; ... }
-        //
-        let mut checks: Vec<Stmt> = vec![];
-        for input in clo.inputs.iter_mut() {
-            match input {
-                Pat::Ident(_) => {}
-                Pat::Type(typed) => {
-                    let ident = pat_ident(&typed.pat)?;
-                    let ty = mem::replace(&mut typed.ty, parse_quote!(_));
-                    match (&*ty).try_into()? {
-                        LuaType::Any => {}
-                        _ => checks.push(parse_quote! { #ident as #ty; }),
-                    }
-                }
-                _ => {}
-            }
-        }
-
-        if !checks.is_empty() {
-            let mut body = wrap_expr_block(&clo.body);
-            body.stmts.splice(..0, checks);
-            clo.body = Box::new(parse_quote! { #body });
-        }
-
-        Ok(())
-    }
-
-    fn transform_function(&mut self, func: &mut ItemFn) -> Result<()> {
-        //
-        // transforms a function item with input type annotations by removing the annotations
-        // and inserting `as` casts at the start.
-        //
-        // before:
-        //    fn my_func(self: table, a: string) { ... }
-        // after:
-        //    fn my_func(self: _, a: _) { self as table; a as string; ... }
-        //
-        let mut checks: Vec<Stmt> = vec![];
-        for input in func.sig.inputs.iter_mut() {
-            if let Some((ident, ty)) = match input {
-                FnArg::Receiver(recv) if recv.colon_token.is_some() => {
-                    let ty = mem::replace(&mut recv.ty, parse_quote!(_));
-                    recv.colon_token = None;
-                    Some((Ident::new("self", recv.self_token.span()), ty))
-                }
-                FnArg::Typed(typed) => {
-                    let ident = pat_ident(&typed.pat)?;
-                    let ty = mem::replace(&mut typed.ty, parse_quote!(_));
-                    Some((ident, ty))
-                }
-                _ => None,
-            } {
-                match (&*ty).try_into()? {
-                    LuaType::Any => {}
-                    _ => checks.push(parse_quote! { #ident as #ty; }),
-                }
-            };
-        }
-
-        func.block.stmts.splice(..0, checks);
-        Ok(())
-    }
-
-    fn transform_expr(&mut self, expr: &mut Expr) -> Result<()> {
-        self.transform_expr_cast(expr)?;
-        Ok(())
-    }
-
-    fn transform_expr_cast(&mut self, expr: &mut Expr) -> Result<()> {
-        //
-        // transforms an `as` cast expression into a block expression containing a runtime
-        // lua type check.
-        //
-        // before:
-        //    var as string
-        // after:
-        //    { if type(var) != "string" { error(...) } }
-        //
-        if let Expr::Cast(cast) = expr {
-            let arg = (*cast.expr).clone();
-            let mut prelude: Option<Stmt> = None;
-            let ty: LuaType = (&*cast.ty).try_into()?;
-            let ty_str = format!("{ty}");
-            let (ident, msg) = match expr_ident(&arg) {
-                Ok(ident) => (ident.clone(), format!("{ty} expected in '{ident}', got ")),
-                Err(_) => {
-                    let ident = Ident::new("_", arg.span());
-                    prelude = Some(parse_quote! { let #ident = #arg; });
-                    (ident, format!("{ty} expected, got "))
-                }
-            };
-
-            let tmp = format_ident!("__{ident}");
-            let span = cast.span();
-            *expr = match ty {
-                LuaType::Any => parse_quote_spanned!(span => {}),
-                LuaType::Nil => parse_quote_spanned!(span => {
-                    #prelude
-                    assert(#ident == (), concat!(#msg, r#type(#ident)));
-                }),
-                LuaType::Number => parse_quote_spanned!(span => {
-                    #prelude
-                    let #tmp = #ident;
-                    #ident = tonumber(#ident);
-                    assert(#ident != (), concat!(#msg, r#type(#tmp)));
-                }),
-                LuaType::Integer => parse_quote_spanned!(span => {
-                    #prelude
-                    let #tmp = #ident;
-                    #ident = tonumber(#ident);
-                    assert(#ident != () && math::floor(#ident) == #ident, concat!(#msg, r#type(#tmp)));
-                }),
-                LuaType::String => parse_quote_spanned!(span => {
-                    #prelude
-                    if r#type(#ident) == "number" {
-                        #ident = tostring(#ident);
-                    } else {
-                        assert(r#type(#ident) == "string", concat!(#msg, r#type(#ident)));
-                    }
-                }),
-                _ => parse_quote_spanned!(span => {
-                    #prelude
-                    assert(r#type(#ident) == #ty_str, concat!(#msg, r#type(#ident)));
-                }),
-            }
-        }
-
-        Ok(())
-    }
-
     fn transform_unary(&mut self, un: &mut ExprUnary) -> Result<()> {
         //
-        // separates a nested negation unary operator with parentheses, because double hyphen
+        // separates a nested negation unary operator with parentheses, because the double hyphen
         // `--` indicates a comment in lua.
         //
         // before:
@@ -216,7 +55,7 @@ impl Visitor {
             && let Expr::Unary(ref inner) = *un.expr
             && let UnOp::Neg(_) = inner.op
         {
-            un.expr = Box::new(parse_quote!((#inner)));
+            un.expr = Box::new(parse_quote_spanned!(inner.span() => (#inner)));
         }
 
         Ok(())
diff --git a/crates/luaify/src/utils.rs b/crates/luaify/src/utils.rs
index d452d4d..3cf6b68 100644
--- a/crates/luaify/src/utils.rs
+++ b/crates/luaify/src/utils.rs
@@ -1,5 +1,4 @@
-use std::fmt;
-use syn::{ext::*, spanned::*, *};
+use syn::*;
 
 macro_rules! syn_error {
     ($src:expr, $($fmt:expr),+) => {{
@@ -24,90 +23,3 @@ pub fn wrap_expr_block(expr: &Expr) -> Block {
         expr => parse_quote!({ #expr }),
     }
 }
-
-pub fn expr_ident(expr: &Expr) -> Result<&Ident> {
-    match expr {
-        Expr::Path(path) => path.path.require_ident(),
-        _ => syn_error!(expr, "expected ident"),
-    }
-}
-
-pub fn pat_ident(pat: &Pat) -> Result<Ident> {
-    Ok(match pat {
-        Pat::Ident(ident) => match ident.subpat {
-            Some((_, ref subpat)) => syn_error!(subpat, "unexpected subpattern"),
-            None => ident.ident.clone(),
-        },
-        Pat::Wild(wild) => Ident::new("_", wild.span()),
-        _ => syn_error!(pat, "expected ident"),
-    })
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum LuaType {
-    Any,
-    Nil,
-    Boolean,
-    Lightuserdata,
-    Number,
-    Integer,
-    String,
-    Table,
-    Function,
-    Userdata,
-    Thread,
-    Cdata,
-}
-
-impl fmt::Display for LuaType {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            LuaType::Any => write!(f, "any"),
-            LuaType::Nil => write!(f, "nil"),
-            LuaType::Boolean => write!(f, "boolean"),
-            LuaType::Lightuserdata => write!(f, "lightuserdata"),
-            LuaType::Number => write!(f, "number"),
-            LuaType::Integer => write!(f, "integer"),
-            LuaType::String => write!(f, "string"),
-            LuaType::Table => write!(f, "table"),
-            LuaType::Function => write!(f, "function"),
-            LuaType::Userdata => write!(f, "userdata"),
-            LuaType::Thread => write!(f, "thread"),
-            LuaType::Cdata => write!(f, "cdata"),
-        }
-    }
-}
-
-impl TryFrom<&Ident> for LuaType {
-    type Error = Error;
-
-    fn try_from(value: &Ident) -> Result<Self> {
-        Ok(match format!("{}", value.unraw()).as_str() {
-            "any" => Self::Any,
-            "nil" => Self::Nil,
-            "boolean" => Self::Boolean,
-            "lightuserdata" => Self::Lightuserdata,
-            "number" => Self::Number,
-            "integer" => Self::Integer,
-            "string" => Self::String,
-            "table" => Self::Table,
-            "function" => Self::Function,
-            "userdata" => Self::Userdata,
-            "thread" => Self::Thread,
-            "cdata" => Self::Cdata,
-            _ => syn_error!(value, "invalid lua type"),
-        })
-    }
-}
-
-impl TryFrom<&Type> for LuaType {
-    type Error = Error;
-
-    fn try_from(value: &Type) -> Result<Self> {
-        match value {
-            Type::Infer(_) => Ok(Self::Any),
-            Type::Path(path) if path.qself.is_none() => path.path.require_ident()?.try_into(),
-            _ => syn_error!(value, "invalid lua type"),
-        }
-    }
-}
diff --git a/crates/luaify/tests/test.rs b/crates/luaify/tests/test.rs
index 78e77ac..70836c0 100644
--- a/crates/luaify/tests/test.rs
+++ b/crates/luaify/tests/test.rs
@@ -77,13 +77,6 @@ fn local_fn() {
         }),
         r#"function(a,b)local function inner(c,d)end;return inner;end"#
     );
-    assert_eq!(
-        luaify!(|| {
-            fn check(self: string, arg: number) {}
-            inner
-        }),
-        r#"function()local function check(self,arg)do if type(self)=="number"then self=tostring(self);else assert(type(self)=="string","string expected in \'self\', got "..type(self));end;end;do local __arg=arg;arg=tonumber(arg);assert(arg~=nil,"number expected in \'arg\', got "..type(__arg));end;end;return inner;end"#
-    );
 }
 
 #[test]
@@ -208,37 +201,6 @@ fn loops() {
     );
 }
 
-#[test]
-fn type_checks() {
-    assert_eq!(luaify!(|s| {}), r#"function(s)end"#);
-    assert_eq!(
-        luaify!(|s: table| {}),
-        r#"function(s)do assert(type(s)=="table","table expected in \'s\', got "..type(s));end;end"#
-    );
-    assert_eq!(
-        luaify!(|s| { s as string }),
-        r#"function(s)do if type(s)=="number"then s=tostring(s);else assert(type(s)=="string","string expected in \'s\', got "..type(s));end;end;end"#
-    );
-    assert_eq!(
-        luaify!(|s| { s as number }),
-        r#"function(s)do local __s=s;s=tonumber(s);assert(s~=nil,"number expected in \'s\', got "..type(__s));end;end"#
-    );
-    assert_eq!(
-        luaify!(|s| { s as nil }),
-        r#"function(s)do assert(s==nil,"nil expected in \'s\', got "..type(s));end;end"#
-    );
-    assert_eq!(luaify!(|s| { s as any }), r#"function(s)do end;end"#);
-
-    assert_eq!(
-        luaify!(|s| {
-            let (ok, res) = coroutine::r#yield(thread);
-            ok as boolean;
-            res as nil;
-        }),
-        r#"function(s)local ok,res=coroutine.yield(thread);do assert(type(ok)=="boolean","boolean expected in \'ok\', got "..type(ok));end;do assert(res==nil,"nil expected in \'res\', got "..type(res));end;end"#
-    );
-}
-
 #[test]
 fn concat() {
     assert_eq!(luaify!(concat!(a)), r#"a"#);