diff --git a/internal/shader/shader.go b/internal/shader/shader.go
index 5c03d19dd..6196930c0 100644
--- a/internal/shader/shader.go
+++ b/internal/shader/shader.go
@@ -19,6 +19,7 @@ import (
 	"go/ast"
 	"go/parser"
 	"go/token"
+	"strconv"
 	"strings"
 
 	"github.com/hajimehoshi/ebiten/internal/shaderir"
@@ -38,8 +39,6 @@ type constant struct {
 
 type function struct {
 	name  string
-	in    []string
-	out   []string
 	block *block
 
 	ir shaderir.Func
@@ -218,39 +217,46 @@ func (cs *compileState) parseFunc(d *ast.FuncDecl, block *block) function {
 		return function{}
 	}
 
-	var in []string
+	var vars []variable
+
 	var inT []shaderir.Type
 	for _, f := range d.Type.Params.List {
 		t := cs.parseType(f.Type)
 		for _, n := range f.Names {
-			in = append(in, n.Name)
+			vars = append(vars, variable{
+				name: n.Name,
+				typ:  t,
+			})
 			inT = append(inT, t.ir)
 		}
 	}
 
-	var out []string
 	var outT []shaderir.Type
 	if d.Type.Results != nil {
 		for _, f := range d.Type.Results.List {
 			t := cs.parseType(f.Type)
 			if len(f.Names) == 0 {
-				out = append(out, "")
+				vars = append(vars, variable{
+					name: "",
+					typ:  t,
+				})
 				outT = append(outT, t.ir)
 			} else {
 				for _, n := range f.Names {
-					out = append(out, n.Name)
+					vars = append(vars, variable{
+						name: n.Name,
+						typ:  t,
+					})
 					outT = append(outT, t.ir)
 				}
 			}
 		}
 	}
 
-	b := cs.parseBlock(block, d.Body)
+	b := cs.parseBlock(block, d.Body, vars)
 
 	return function{
 		name:  d.Name.Name,
-		in:    in,
-		out:   out,
 		block: b,
 		ir: shaderir.Func{
 			Index:     len(cs.ir.Funcs),
@@ -261,8 +267,9 @@ func (cs *compileState) parseFunc(d *ast.FuncDecl, block *block) function {
 	}
 }
 
-func (cs *compileState) parseBlock(outer *block, b *ast.BlockStmt) *block {
+func (cs *compileState) parseBlock(outer *block, b *ast.BlockStmt, locals []variable) *block {
 	block := &block{
+		vars:  locals,
 		outer: outer,
 	}
 
@@ -304,7 +311,7 @@ func (cs *compileState) parseBlock(outer *block, b *ast.BlockStmt) *block {
 			cs.parseDecl(block, l.Decl, false)
 		case *ast.ReturnStmt:
 			for _, r := range l.Results {
-				e := cs.parseExpr(r)
+				e := cs.parseExpr(block, r)
 				block.ir.Stmts = append(block.ir.Stmts, shaderir.Stmt{
 					Type: shaderir.Assign,
 					Exprs: []shaderir.Expr{
@@ -369,22 +376,74 @@ func (s *compileState) detectType(b *block, expr ast.Expr) typ {
 	}
 }
 
-func (cs *compileState) parseExpr(expr ast.Expr) shaderir.Expr {
+func (b *block) findLocalVariable(name string) (int, bool) {
+	for i, v := range b.vars {
+		if v.name == name {
+			return i, true
+		}
+	}
+	if b.outer != nil {
+		return b.outer.findLocalVariable(name)
+	}
+	return 0, false
+}
+
+func (cs *compileState) parseExpr(block *block, expr ast.Expr) shaderir.Expr {
 	switch e := expr.(type) {
+	case *ast.BasicLit:
+		switch e.Kind {
+		case token.INT:
+			v, err := strconv.ParseInt(e.Value, 10, 32)
+			if err != nil {
+				cs.addError(e.Pos(), fmt.Sprintf("unexpected literal: %s", e.Value))
+				return shaderir.Expr{}
+			}
+			return shaderir.Expr{
+				Type: shaderir.IntExpr,
+				Int:  int32(v),
+			}
+		case token.FLOAT:
+			v, err := strconv.ParseFloat(e.Value, 32)
+			if err != nil {
+				cs.addError(e.Pos(), fmt.Sprintf("unexpected literal: %s", e.Value))
+				return shaderir.Expr{}
+			}
+			return shaderir.Expr{
+				Type:  shaderir.FloatExpr,
+				Float: float32(v),
+			}
+		default:
+			cs.addError(e.Pos(), fmt.Sprintf("literal not implemented: %#v", e))
+		}
 	case *ast.CallExpr:
+		exprs := []shaderir.Expr{
+			cs.parseExpr(block, e.Fun),
+		}
+		for _, a := range e.Args {
+			exprs = append(exprs, cs.parseExpr(block, a))
+		}
 		return shaderir.Expr{
-			Type: shaderir.Call,
-			Exprs: []shaderir.Expr{
-				cs.parseExpr(e.Fun),
-			},
+			Type:  shaderir.Call,
+			Exprs: exprs,
 		}
 	case *ast.Ident:
-		return shaderir.Expr{
-			Type:        shaderir.BuiltinFuncExpr,
-			BuiltinFunc: shaderir.BuiltinFunc(e.Name),
+		i, ok := block.findLocalVariable(e.Name)
+		if ok {
+			return shaderir.Expr{
+				Type:  shaderir.LocalVariable,
+				Index: i,
+			}
 		}
+		f, ok := shaderir.ParseBuiltinFunc(e.Name)
+		if ok {
+			return shaderir.Expr{
+				Type:        shaderir.BuiltinFuncExpr,
+				BuiltinFunc: f,
+			}
+		}
+		cs.addError(e.Pos(), fmt.Sprintf("unexpected identifier: %s", e.Name))
 	default:
-		cs.addError(expr.Pos(), fmt.Sprintf("detecting expression not implemented: %#v", e))
+		cs.addError(e.Pos(), fmt.Sprintf("expression not implemented: %#v", e))
 	}
 	return shaderir.Expr{}
 }
diff --git a/internal/shaderir/program.go b/internal/shaderir/program.go
index e9fbc62b0..3b1177eee 100644
--- a/internal/shaderir/program.go
+++ b/internal/shaderir/program.go
@@ -192,3 +192,63 @@ const (
 	Not              BuiltinFunc = "not"
 	Texture2DF       BuiltinFunc = "texture2D"
 )
+
+func ParseBuiltinFunc(str string) (BuiltinFunc, bool) {
+	switch BuiltinFunc(str) {
+	case Vec2F,
+		Vec3F,
+		Vec4F,
+		Mat2F,
+		Mat3F,
+		Mat4F,
+		Radians,
+		Degrees,
+		Sin,
+		Cos,
+		Tan,
+		Asin,
+		Acos,
+		Atan,
+		Pow,
+		Exp,
+		Log,
+		Exp2,
+		Log2,
+		Sqrt,
+		Inversesqrt,
+		Abs,
+		Sign,
+		Floor,
+		Ceil,
+		Fract,
+		Mod,
+		Min,
+		Max,
+		Clamp,
+		Mix,
+		Step,
+		Smoothstep,
+		Length,
+		Distance,
+		Dot,
+		Cross,
+		Normalize,
+		Faceforward,
+		Reflect,
+		MatrixCompMult,
+		OuterProduct,
+		Transpose,
+		LessThan,
+		LessThanEqual,
+		GreaterThan,
+		GreaterThanEqual,
+		Equal,
+		NotEqual,
+		Any,
+		All,
+		Not,
+		Texture2DF:
+		return BuiltinFunc(str), true
+	}
+	return "", false
+}