diff --git a/libjulia/optimiser/ASTCopier.h b/libjulia/optimiser/ASTCopier.h
index 0658fd509..5dde2ce9d 100644
--- a/libjulia/optimiser/ASTCopier.h
+++ b/libjulia/optimiser/ASTCopier.h
@@ -56,6 +56,8 @@ public:
 	Statement operator()(ForLoop const&);
 	Statement operator()(Block const& _block);
 
+	virtual Statement translate(Statement const& _statement);
+
 protected:
 	template <typename T>
 	std::vector<T> translateVector(std::vector<T> const& _values);
@@ -65,7 +67,6 @@ protected:
 	{
 		return _v ? std::make_shared<T>(translate(*_v)) : nullptr;
 	}
-	Statement translate(Statement const& _statement);
 	Block translate(Block const& _block);
 	Case translate(Case const& _case);
 	Identifier translate(Identifier const& _identifier);
diff --git a/libjulia/optimiser/ASTWalker.cpp b/libjulia/optimiser/ASTWalker.cpp
index 786afbe07..0caef04e0 100644
--- a/libjulia/optimiser/ASTWalker.cpp
+++ b/libjulia/optimiser/ASTWalker.cpp
@@ -104,24 +104,24 @@ void ASTModifier::operator()(Assignment& _assignment)
 {
 	for (auto& name: _assignment.variableNames)
 		(*this)(name);
-	boost::apply_visitor(*this, *_assignment.value);
+	visit(*_assignment.value);
 }
 
 void ASTModifier::operator()(VariableDeclaration& _varDecl)
 {
 	if (_varDecl.value)
-		boost::apply_visitor(*this, *_varDecl.value);
+		visit(*_varDecl.value);
 }
 
 void ASTModifier::operator()(If& _if)
 {
-	boost::apply_visitor(*this, *_if.condition);
+	visit(*_if.condition);
 	(*this)(_if.body);
 }
 
 void ASTModifier::operator()(Switch& _switch)
 {
-	boost::apply_visitor(*this, *_switch.expression);
+	visit(*_switch.expression);
 	for (auto& _case: _switch.cases)
 	{
 		if (_case.value)
@@ -138,7 +138,7 @@ void ASTModifier::operator()(FunctionDefinition& _fun)
 void ASTModifier::operator()(ForLoop& _for)
 {
 	(*this)(_for.pre);
-	boost::apply_visitor(*this, *_for.condition);
+	visit(*_for.condition);
 	(*this)(_for.post);
 	(*this)(_for.body);
 }
diff --git a/libjulia/optimiser/ASTWalker.h b/libjulia/optimiser/ASTWalker.h
index 01499a503..8bd867d5a 100644
--- a/libjulia/optimiser/ASTWalker.h
+++ b/libjulia/optimiser/ASTWalker.h
@@ -92,7 +92,11 @@ protected:
 	void walkVector(T&& _statements)
 	{
 		for (auto& st: _statements)
-			boost::apply_visitor(*this, st);
+			visit(st);
+	}
+	virtual void visit(Statement& _st)
+	{
+		boost::apply_visitor(*this, _st);
 	}
 };
 
diff --git a/libjulia/optimiser/Substitution.cpp b/libjulia/optimiser/Substitution.cpp
new file mode 100644
index 000000000..a49f1f7a7
--- /dev/null
+++ b/libjulia/optimiser/Substitution.cpp
@@ -0,0 +1,39 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * Specific AST copier that replaces certain identifiers with expressions.
+ */
+
+#include <libjulia/optimiser/Substitution.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::julia;
+
+Statement Substitution::translate(Statement const& _statement)
+{
+	if (_statement.type() == typeid(Identifier))
+	{
+		string const& name = boost::get<Identifier>(_statement).name;
+		if (m_substitutions.count(name))
+			// No recursive substitution
+			return ASTCopier().translate(*m_substitutions.at(name));
+	}
+	return ASTCopier::translate(_statement);
+}
diff --git a/libjulia/optimiser/Substitution.h b/libjulia/optimiser/Substitution.h
new file mode 100644
index 000000000..10bdf32e6
--- /dev/null
+++ b/libjulia/optimiser/Substitution.h
@@ -0,0 +1,51 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * Specific AST copier that replaces certain identifiers with expressions.
+ */
+
+#pragma once
+
+#include <libjulia/optimiser/ASTCopier.h>
+
+#include <string>
+#include <map>
+#include <set>
+
+namespace dev
+{
+namespace julia
+{
+
+/**
+ * Specific AST copier that replaces certain identifiers with expressions.
+ * Only works on ASTs that are expressions.
+ */
+class Substitution: public ASTCopier
+{
+public:
+	Substitution(std::map<std::string, Statement const*> const& _substitutions):
+		m_substitutions(_substitutions)
+	{}
+	virtual Statement translate(Statement const& _statement) override;
+
+private:
+	std::map<std::string, Statement const*> const& m_substitutions;
+};
+
+}
+}