diff --git a/il65/compile.py b/il65/compile.py
index 4feb3a4bf..a10ebe90f 100644
--- a/il65/compile.py
+++ b/il65/compile.py
@@ -11,9 +11,10 @@ import sys
 import linecache
 from typing import Optional, Tuple, Set, Dict, List, Any, no_type_check
 import attr
-from .plyparse import *
-from .plylex import SourceRef, print_bold
 from .datatypes import DataType, VarType
+from .plylex import SourceRef, print_bold
+from .expressions import ExpressionOptimizer
+from .plyparse import *
 
 
 class CompileError(Exception):
@@ -42,6 +43,8 @@ class PlyParser:
                 self.check_all_symbolnames(module)
                 self.determine_subroutine_usage(module)
                 self.all_parents_connected(module)
+                eo = ExpressionOptimizer(module)
+                eo.optimize()   # do some constant-folding
                 self.semantic_check(module)
                 self.coerce_values(module)
                 self.check_floats_enabled(module)
diff --git a/il65/expressions.py b/il65/expressions.py
new file mode 100644
index 000000000..8b30983bf
--- /dev/null
+++ b/il65/expressions.py
@@ -0,0 +1,220 @@
+"""
+Programming Language for 6502/6510 microprocessors, codename 'Sick'
+This is the part of the compiler/optimizer that simplifies/evaluates expressions.
+
+Written by Irmen de Jong (irmen@razorvine.net) - license: GNU GPL 3.0
+"""
+
+import sys
+from .plylex import SourceRef
+from .datatypes import VarType
+from .plyparse import Module, Expression, LiteralValue, SymbolName, ParseError, VarDef, Dereference, Register,\
+    SubCall, AddressOf, AstNode, ExpressionWithOperator, ExpressionEvaluationError, \
+    math_functions, builtin_functions, check_symbol_definition
+
+
+def handle_internal_error(exc: Exception, msg: str = "") -> None:
+    out = sys.stdout
+    if out.isatty():
+        print("\x1b[1m", file=out)
+    print("\nERROR: internal parser/optimizer error: ", exc, file=out)
+    if msg:
+        print("    Message:", msg, end="\n\n")
+    if out.isatty():
+        print("\x1b[0m", file=out, end="", flush=True)
+    raise exc
+
+
+class ExpressionOptimizer:
+    def __init__(self, mod: Module) -> None:
+        self.num_warnings = 0
+        self.module = mod
+        self.optimizations_performed = False
+
+    def optimize(self, once: bool=False) -> None:
+        self.num_warnings = 0
+        if once:
+            self.constant_folding()
+        else:
+            self.optimizations_performed = True
+            # keep optimizing as long as there were changes made
+            while self.optimizations_performed:
+                self.optimizations_performed = False
+                self.constant_folding()
+
+    def constant_folding(self) -> None:
+        for expression in self.module.all_nodes(Expression):
+            if isinstance(expression, LiteralValue):
+                continue
+            try:
+                evaluated = self.process_expression(expression)      # type: ignore
+                if evaluated is not expression:
+                    # replace the node with the newly evaluated result
+                    parent = expression.parent
+                    parent.replace_node(expression, evaluated)
+                    self.optimizations_performed = True
+            except ParseError:
+                raise
+            except Exception as x:
+                handle_internal_error(x, "process_expressions of node {}".format(expression))
+
+    def process_expression(self, expr: Expression) -> Expression:
+        # process/simplify all expressions (constant folding etc)
+        result = None   # type: Expression
+        if expr.is_compile_constant() or isinstance(expr, ExpressionWithOperator) and expr.must_be_constant:
+            result = self._process_constant_expression(expr, expr.sourceref)
+        else:
+            result = self._process_dynamic_expression(expr, expr.sourceref)
+        result.parent = expr.parent
+        return result
+
+    def _process_constant_expression(self, expr: Expression, sourceref: SourceRef) -> LiteralValue:
+        # the expression must result in a single (constant) value (int, float, whatever) wrapped as LiteralValue.
+        if isinstance(expr, LiteralValue):
+            return expr
+        if expr.is_compile_constant():
+            return LiteralValue(value=expr.const_value(), sourceref=sourceref)  # type: ignore
+        elif isinstance(expr, SymbolName):
+            value = check_symbol_definition(expr.name, expr.my_scope(), expr.sourceref)
+            if isinstance(value, VarDef):
+                if value.vartype == VarType.MEMORY:
+                    raise ExpressionEvaluationError("can't take a memory value, must be a constant", expr.sourceref)
+                value = value.value
+            if isinstance(value, ExpressionWithOperator):
+                raise ExpressionEvaluationError("circular reference?", expr.sourceref)
+            elif isinstance(value, LiteralValue):
+                return value
+            elif isinstance(value, (int, float, str, bool)):
+                raise TypeError("symbol value node should not be a python primitive value", expr)
+            else:
+                raise ExpressionEvaluationError("constant symbol required, not {}".format(value.__class__.__name__), expr.sourceref)
+        elif isinstance(expr, AddressOf):
+            assert isinstance(expr.name, str)
+            value = check_symbol_definition(expr.name, expr.my_scope(), expr.sourceref)
+            if isinstance(value, VarDef):
+                if value.vartype == VarType.MEMORY:
+                    if isinstance(value.value, LiteralValue):
+                        return value.value
+                    else:
+                        raise ExpressionEvaluationError("constant literal value required", value.sourceref)
+                if value.vartype == VarType.CONST:
+                    raise ExpressionEvaluationError("can't take the address of a constant", expr.sourceref)
+                raise ExpressionEvaluationError("address-of this {} isn't a compile-time constant"
+                                                .format(value.__class__.__name__), expr.sourceref)
+            else:
+                raise ExpressionEvaluationError("constant address required, not {}"
+                                                .format(value.__class__.__name__), expr.sourceref)
+        elif isinstance(expr, SubCall):
+            if isinstance(expr.target, SymbolName):      # 'function(1,2,3)'
+                funcname = expr.target.name
+                if funcname in math_functions or funcname in builtin_functions:
+                    func_args = []
+                    for a in (self._process_constant_expression(callarg.value, sourceref) for callarg in list(expr.arguments.nodes)):
+                        if isinstance(a, LiteralValue):
+                            func_args.append(a.value)
+                        else:
+                            func_args.append(a)
+                    func = math_functions.get(funcname, builtin_functions.get(funcname))
+                    try:
+                        return LiteralValue(value=func(*func_args), sourceref=expr.arguments.sourceref)  # type: ignore
+                    except Exception as x:
+                        raise ExpressionEvaluationError(str(x), expr.sourceref)
+                else:
+                    raise ExpressionEvaluationError("can only use math- or builtin function", expr.sourceref)
+            elif isinstance(expr.target, Dereference):       # '[...](1,2,3)'
+                raise ExpressionEvaluationError("dereferenced value call is not a constant value", expr.sourceref)
+            elif isinstance(expr.target, LiteralValue) and type(expr.target.value) is int:   # '64738()'
+                raise ExpressionEvaluationError("immediate address call is not a constant value", expr.sourceref)
+            else:
+                raise NotImplementedError("weird call target", expr.target)
+        elif isinstance(expr, ExpressionWithOperator):
+            if expr.unary:
+                left_sourceref = expr.left.sourceref if isinstance(expr.left, AstNode) else sourceref
+                expr.left = self._process_constant_expression(expr.left, left_sourceref)
+                expr.left.parent = expr
+                if isinstance(expr.left, LiteralValue) and type(expr.left.value) in (int, float):
+                    try:
+                        if expr.operator == '-':
+                            return LiteralValue(value=-expr.left.value, sourceref=expr.left.sourceref)  # type: ignore
+                        elif expr.operator == '~':
+                            return LiteralValue(value=~expr.left.value, sourceref=expr.left.sourceref)  # type: ignore
+                        elif expr.operator in ("++", "--"):
+                            raise ValueError("incr/decr should not be an expression")
+                        raise ValueError("invalid unary operator", expr.operator)
+                    except TypeError as x:
+                        raise ParseError(str(x), expr.sourceref) from None
+                raise ValueError("invalid operand type for unary operator", expr.left, expr.operator)
+            else:
+                left_sourceref = expr.left.sourceref if isinstance(expr.left, AstNode) else sourceref
+                expr.left = self._process_constant_expression(expr.left, left_sourceref)
+                expr.left.parent = expr
+                right_sourceref = expr.right.sourceref if isinstance(expr.right, AstNode) else sourceref
+                expr.right = self._process_constant_expression(expr.right, right_sourceref)
+                expr.right.parent = expr
+                if isinstance(expr.left, LiteralValue):
+                    if isinstance(expr.right, LiteralValue):
+                        return expr.evaluate_primitive_constants(expr.right.sourceref)
+                    else:
+                        raise ExpressionEvaluationError("constant literal value required on right, not {}"
+                                                        .format(expr.right.__class__.__name__), right_sourceref)
+                else:
+                    raise ExpressionEvaluationError("constant literal value required on left, not {}"
+                                                    .format(expr.left.__class__.__name__), left_sourceref)
+        else:
+            raise ExpressionEvaluationError("constant value required, not {}".format(expr.__class__.__name__), expr.sourceref)
+
+    def _process_dynamic_expression(self, expr: Expression, sourceref: SourceRef) -> Expression:
+        # constant-fold a dynamic expression
+        if isinstance(expr, LiteralValue):
+            return expr
+        if expr.is_compile_constant():
+            return LiteralValue(value=expr.const_value(), sourceref=sourceref)  # type: ignore
+        elif isinstance(expr, SymbolName):
+            if expr.is_compile_constant():
+                try:
+                    return self._process_constant_expression(expr, sourceref)
+                except ExpressionEvaluationError:
+                    pass
+            return expr
+        elif isinstance(expr, AddressOf):
+            if expr.is_compile_constant():
+                try:
+                    return self._process_constant_expression(expr, sourceref)
+                except ExpressionEvaluationError:
+                    pass
+            return expr
+        elif isinstance(expr, SubCall):
+            try:
+                return self._process_constant_expression(expr, sourceref)
+            except ExpressionEvaluationError:
+                if isinstance(expr.target, SymbolName):
+                    check_symbol_definition(expr.target.name, expr.my_scope(), expr.target.sourceref)
+                return expr
+        elif isinstance(expr, (Register, Dereference)):
+            return expr
+        elif isinstance(expr, ExpressionWithOperator):
+            if expr.unary:
+                left_sourceref = expr.left.sourceref if isinstance(expr.left, AstNode) else sourceref
+                expr.left = self._process_dynamic_expression(expr.left, left_sourceref)
+                expr.left.parent = expr
+                if expr.is_compile_constant():
+                    try:
+                        return self._process_constant_expression(expr, sourceref)
+                    except ExpressionEvaluationError:
+                        pass
+                return expr
+            else:
+                left_sourceref = expr.left.sourceref if isinstance(expr.left, AstNode) else sourceref
+                expr.left = self._process_dynamic_expression(expr.left, left_sourceref)
+                expr.left.parent = expr
+                right_sourceref = expr.right.sourceref if isinstance(expr.right, AstNode) else sourceref
+                expr.right = self._process_dynamic_expression(expr.right, right_sourceref)
+                expr.right.parent = expr
+                if expr.is_compile_constant():
+                    try:
+                        return self._process_constant_expression(expr, sourceref)
+                    except ExpressionEvaluationError:
+                        pass
+                return expr
+        else:
+            raise ParseError("expression required, not {}".format(expr.__class__.__name__), expr.sourceref)
diff --git a/il65/optimize.py b/il65/optimize.py
index dc738ac97..fe56f131f 100644
--- a/il65/optimize.py
+++ b/il65/optimize.py
@@ -6,11 +6,13 @@ eliminates statements that have no effect, optimizes calculations etc.
 Written by Irmen de Jong (irmen@razorvine.net) - license: GNU GPL 3.0
 """
 
-import sys
-from typing import List, no_type_check, Union, Any
-from .plyparse import *
-from .plylex import print_warning, print_bold, SourceRef
-from .datatypes import DataType, VarType
+from typing import List, no_type_check, Union
+from .datatypes import DataType
+from .plyparse import Module, Block, Scope, IncrDecr, AstNode, Register, TargetRegisters, Assignment, AugAssignment, \
+    AssignmentTargets, SymbolName, VarDef, Dereference, LiteralValue, ExpressionWithOperator, Subroutine, \
+    Goto, Expression, Directive, coerce_constant_value, datatype_of
+from .plylex import print_warning, print_bold
+from .expressions import ExpressionOptimizer
 
 
 class Optimizer:
@@ -18,6 +20,7 @@ class Optimizer:
         self.num_warnings = 0
         self.module = mod
         self.optimizations_performed = False
+        self.simple_expression_optimizer = ExpressionOptimizer(self.module)
 
     def optimize(self) -> None:
         self.num_warnings = 0
@@ -31,7 +34,7 @@ class Optimizer:
         self.remove_empty_blocks()
 
     def _optimize(self) -> None:
-        self.constant_folding()
+        self.simple_expression_optimizer.optimize(True)    # perform constant folding and simple expression optimization
         # @todo expression optimization: reduce expression nesting / flattening of parenthesis
         # @todo expression optimization: simplify logical expression when a term makes it always true or false
         # @todo expression optimization: optimize some simple multiplications into shifts  (A*=8 -> A<<3)
@@ -47,33 +50,6 @@ class Optimizer:
         # @todo remove loops with conditions that are always empty/false
         # @todo analyse for unreachable code and remove that (f.i. code after goto or return that has no label so can never be jumped to)
 
-    def handle_internal_error(self, exc: Exception, msg: str="") -> None:
-        out = sys.stdout
-        if out.isatty():
-            print("\x1b[1m", file=out)
-        print("\nERROR: internal parser/optimizer error: ", exc, file=out)
-        if msg:
-            print("    Message:", msg, end="\n\n")
-        if out.isatty():
-            print("\x1b[0m", file=out, end="", flush=True)
-        raise exc
-
-    def constant_folding(self) -> None:
-        for expression in self.module.all_nodes(Expression):
-            if isinstance(expression, LiteralValue):
-                continue
-            try:
-                evaluated = process_expression(expression)    # type: ignore
-                if evaluated is not expression:
-                    # replace the node with the newly evaluated result
-                    parent = expression.parent
-                    parent.replace_node(expression, evaluated)
-                    self.optimizations_performed = True
-            except ParseError:
-                raise
-            except Exception as x:
-                self.handle_internal_error(x, "process_expressions of node {}".format(expression))
-
     def join_incrdecrs(self) -> None:
         for scope in self.module.all_nodes(Scope):
             incrdecrs = []      # type: List[IncrDecr]
@@ -399,170 +375,6 @@ class Optimizer:
                     node.my_scope().nodes.remove(node)
 
 
-def process_expression(expr: Expression) -> Expression:
-    # process/simplify all expressions (constant folding etc)
-    result = None   # type: Expression
-    if expr.is_compile_constant() or isinstance(expr, ExpressionWithOperator) and expr.must_be_constant:
-        result = _process_constant_expression(expr, expr.sourceref)
-    else:
-        result = _process_dynamic_expression(expr, expr.sourceref)
-    result.parent = expr.parent
-    return result
-
-
-def _process_constant_expression(expr: Expression, sourceref: SourceRef) -> LiteralValue:
-    # the expression must result in a single (constant) value (int, float, whatever) wrapped as LiteralValue.
-    if isinstance(expr, LiteralValue):
-        return expr
-    if expr.is_compile_constant():
-        return LiteralValue(value=expr.const_value(), sourceref=sourceref)  # type: ignore
-    elif isinstance(expr, SymbolName):
-        value = check_symbol_definition(expr.name, expr.my_scope(), expr.sourceref)
-        if isinstance(value, VarDef):
-            if value.vartype == VarType.MEMORY:
-                raise ExpressionEvaluationError("can't take a memory value, must be a constant", expr.sourceref)
-            value = value.value
-        if isinstance(value, ExpressionWithOperator):
-            raise ExpressionEvaluationError("circular reference?", expr.sourceref)
-        elif isinstance(value, LiteralValue):
-            return value
-        elif isinstance(value, (int, float, str, bool)):
-            raise TypeError("symbol value node should not be a python primitive value", expr)
-        else:
-            raise ExpressionEvaluationError("constant symbol required, not {}".format(value.__class__.__name__), expr.sourceref)
-    elif isinstance(expr, AddressOf):
-        assert isinstance(expr.name, str)
-        value = check_symbol_definition(expr.name, expr.my_scope(), expr.sourceref)
-        if isinstance(value, VarDef):
-            if value.vartype == VarType.MEMORY:
-                if isinstance(value.value, LiteralValue):
-                    return value.value
-                else:
-                    raise ExpressionEvaluationError("constant literal value required", value.sourceref)
-            if value.vartype == VarType.CONST:
-                raise ExpressionEvaluationError("can't take the address of a constant", expr.sourceref)
-            raise ExpressionEvaluationError("address-of this {} isn't a compile-time constant"
-                                            .format(value.__class__.__name__), expr.sourceref)
-        else:
-            raise ExpressionEvaluationError("constant address required, not {}"
-                                            .format(value.__class__.__name__), expr.sourceref)
-    elif isinstance(expr, SubCall):
-        if isinstance(expr.target, SymbolName):      # 'function(1,2,3)'
-            funcname = expr.target.name
-            if funcname in math_functions or funcname in builtin_functions:
-                func_args = []
-                for a in (_process_constant_expression(callarg.value, sourceref) for callarg in list(expr.arguments.nodes)):
-                    if isinstance(a, LiteralValue):
-                        func_args.append(a.value)
-                    else:
-                        func_args.append(a)
-                func = math_functions.get(funcname, builtin_functions.get(funcname))
-                try:
-                    return LiteralValue(value=func(*func_args), sourceref=expr.arguments.sourceref)  # type: ignore
-                except Exception as x:
-                    raise ExpressionEvaluationError(str(x), expr.sourceref)
-            else:
-                raise ExpressionEvaluationError("can only use math- or builtin function", expr.sourceref)
-        elif isinstance(expr.target, Dereference):       # '[...](1,2,3)'
-            raise ExpressionEvaluationError("dereferenced value call is not a constant value", expr.sourceref)
-        elif isinstance(expr.target, LiteralValue) and type(expr.target.value) is int:   # '64738()'
-            raise ExpressionEvaluationError("immediate address call is not a constant value", expr.sourceref)
-        else:
-            raise NotImplementedError("weird call target", expr.target)
-    elif isinstance(expr, ExpressionWithOperator):
-        if expr.unary:
-            left_sourceref = expr.left.sourceref if isinstance(expr.left, AstNode) else sourceref
-            expr.left = _process_constant_expression(expr.left, left_sourceref)
-            expr.left.parent = expr
-            if isinstance(expr.left, LiteralValue) and type(expr.left.value) in (int, float):
-                try:
-                    if expr.operator == '-':
-                        return LiteralValue(value=-expr.left.value, sourceref=expr.left.sourceref)  # type: ignore
-                    elif expr.operator == '~':
-                        return LiteralValue(value=~expr.left.value, sourceref=expr.left.sourceref)  # type: ignore
-                    elif expr.operator in ("++", "--"):
-                        raise ValueError("incr/decr should not be an expression")
-                    raise ValueError("invalid unary operator", expr.operator)
-                except TypeError as x:
-                    raise ParseError(str(x), expr.sourceref) from None
-            raise ValueError("invalid operand type for unary operator", expr.left, expr.operator)
-        else:
-            left_sourceref = expr.left.sourceref if isinstance(expr.left, AstNode) else sourceref
-            expr.left = _process_constant_expression(expr.left, left_sourceref)
-            expr.left.parent = expr
-            right_sourceref = expr.right.sourceref if isinstance(expr.right, AstNode) else sourceref
-            expr.right = _process_constant_expression(expr.right, right_sourceref)
-            expr.right.parent = expr
-            if isinstance(expr.left, LiteralValue):
-                if isinstance(expr.right, LiteralValue):
-                    return expr.evaluate_primitive_constants(expr.right.sourceref)
-                else:
-                    raise ExpressionEvaluationError("constant literal value required on right, not {}"
-                                                    .format(expr.right.__class__.__name__), right_sourceref)
-            else:
-                raise ExpressionEvaluationError("constant literal value required on left, not {}"
-                                                .format(expr.left.__class__.__name__), left_sourceref)
-    else:
-        raise ExpressionEvaluationError("constant value required, not {}".format(expr.__class__.__name__), expr.sourceref)
-
-
-def _process_dynamic_expression(expr: Expression, sourceref: SourceRef) -> Expression:
-    # constant-fold a dynamic expression
-    if isinstance(expr, LiteralValue):
-        return expr
-    if expr.is_compile_constant():
-        return LiteralValue(value=expr.const_value(), sourceref=sourceref)  # type: ignore
-    elif isinstance(expr, SymbolName):
-        if expr.is_compile_constant():
-            try:
-                return _process_constant_expression(expr, sourceref)
-            except ExpressionEvaluationError:
-                pass
-        return expr
-    elif isinstance(expr, AddressOf):
-        if expr.is_compile_constant():
-            try:
-                return _process_constant_expression(expr, sourceref)
-            except ExpressionEvaluationError:
-                pass
-        return expr
-    elif isinstance(expr, SubCall):
-        try:
-            return _process_constant_expression(expr, sourceref)
-        except ExpressionEvaluationError:
-            if isinstance(expr.target, SymbolName):
-                check_symbol_definition(expr.target.name, expr.my_scope(), expr.target.sourceref)
-            return expr
-    elif isinstance(expr, (Register, Dereference)):
-        return expr
-    elif isinstance(expr, ExpressionWithOperator):
-        if expr.unary:
-            left_sourceref = expr.left.sourceref if isinstance(expr.left, AstNode) else sourceref
-            expr.left = _process_dynamic_expression(expr.left, left_sourceref)
-            expr.left.parent = expr
-            if expr.is_compile_constant():
-                try:
-                    return _process_constant_expression(expr, sourceref)
-                except ExpressionEvaluationError:
-                    pass
-            return expr
-        else:
-            left_sourceref = expr.left.sourceref if isinstance(expr.left, AstNode) else sourceref
-            expr.left = _process_dynamic_expression(expr.left, left_sourceref)
-            expr.left.parent = expr
-            right_sourceref = expr.right.sourceref if isinstance(expr.right, AstNode) else sourceref
-            expr.right = _process_dynamic_expression(expr.right, right_sourceref)
-            expr.right.parent = expr
-            if expr.is_compile_constant():
-                try:
-                    return _process_constant_expression(expr, sourceref)
-                except ExpressionEvaluationError:
-                    pass
-            return expr
-    else:
-        raise ParseError("expression required, not {}".format(expr.__class__.__name__), expr.sourceref)
-
-
 def optimize(mod: Module) -> None:
     opt = Optimizer(mod)
     opt.optimize()
diff --git a/il65/plyparse.py b/il65/plyparse.py
index c61e86001..f4f858510 100644
--- a/il65/plyparse.py
+++ b/il65/plyparse.py
@@ -472,7 +472,8 @@ class AddressOf(Expression):
     def is_compile_constant(self) -> bool:
         # address-of can be a compile time constant if the operand is a memory mapped variable or ZP variable
         symdef = self.my_scope().lookup(self.name)
-        return isinstance(symdef, VarDef) and symdef.vartype == VarType.MEMORY or getattr(symdef, "zp_address", None) is not None   # type: ignore
+        return isinstance(symdef, VarDef) and symdef.vartype == VarType.MEMORY \
+            or getattr(symdef, "zp_address", None) is not None   # type: ignore
 
     def const_value(self) -> Union[int, float, bool, str]:
         symdef = self.my_scope().lookup(self.name)