diff --git a/vhdlpp/debug.cc b/vhdlpp/debug.cc
index 0ef95667e..e75835599 100644
--- a/vhdlpp/debug.cc
+++ b/vhdlpp/debug.cc
@@ -145,13 +145,19 @@ void ExpArithmetic::dump(ostream&out, int indent) const
 
       out << setw(indent) << "" << "Arithmetic " << fun_name
 	  << " at " << get_fileline() << endl;
-      operand1()->dump(out, indent+4);
-      operand2()->dump(out, indent+4);
+      dump_operands(out, indent+4);
+}
+
+void ExpBinary::dump_operands(ostream&out, int indent) const
+{
+      operand1_->dump(out, indent);
+      operand2_->dump(out, indent);
 }
 
 void ExpInteger::dump(ostream&out, int indent) const
 {
-      out << setw(indent) << "" << "Integer" << endl;
+      out << setw(indent) << "" << "Integer " << value_
+	  << " at " << get_fileline() << endl;
 }
 
 void ExpLogical::dump(ostream&out, int indent) const
@@ -180,8 +186,7 @@ void ExpLogical::dump(ostream&out, int indent) const
 
       out << setw(indent) << "" << "Logical " << fun_name
 	  << " at " << get_fileline() << endl;
-      operand1()->dump(out, indent+4);
-      operand2()->dump(out, indent+4);
+      dump_operands(out, indent+4);
 }
 
 void ExpName::dump(ostream&out, int indent) const
@@ -189,3 +194,20 @@ void ExpName::dump(ostream&out, int indent) const
       out << setw(indent) << "" << "ExpName(\"" << name_ << "\")"
 	  << " at " << get_fileline() << endl;
 }
+
+void ExpUAbs::dump(ostream&out, int indent) const
+{
+      out << setw(indent) << "" << "abs() at " << get_fileline() << endl;
+      dump_operand1(out, indent+4);
+}
+
+void ExpUnary::dump_operand1(ostream&out, int indent) const
+{
+      operand1_->dump(out, indent);
+}
+
+void ExpUNot::dump(ostream&out, int indent) const
+{
+      out << setw(indent) << "" << "not() at " << get_fileline() << endl;
+      dump_operand1(out, indent+4);
+}
diff --git a/vhdlpp/expression.cc b/vhdlpp/expression.cc
index 3021cd833..823b52fff 100644
--- a/vhdlpp/expression.cc
+++ b/vhdlpp/expression.cc
@@ -43,6 +43,16 @@ ExpBinary::~ExpBinary()
       delete operand2_;
 }
 
+ExpUnary::ExpUnary(Expression*op1)
+: operand1_(op1)
+{
+}
+
+ExpUnary::~ExpUnary()
+{
+      delete operand1_;
+}
+
 ExpArithmetic::ExpArithmetic(ExpArithmetic::fun_t op, Expression*op1, Expression*op2)
 : ExpBinary(op1, op2), fun_(op)
 {
@@ -84,3 +94,21 @@ ExpName::ExpName(perm_string nn)
 ExpName::~ExpName()
 {
 }
+
+ExpUAbs::ExpUAbs(Expression*op1)
+: ExpUnary(op1)
+{
+}
+
+ExpUAbs::~ExpUAbs()
+{
+}
+
+ExpUNot::ExpUNot(Expression*op1)
+: ExpUnary(op1)
+{
+}
+
+ExpUNot::~ExpUNot()
+{
+}
diff --git a/vhdlpp/expression.h b/vhdlpp/expression.h
index 2b7f197f9..ec540acd0 100644
--- a/vhdlpp/expression.h
+++ b/vhdlpp/expression.h
@@ -48,6 +48,13 @@ class Expression : public LineInfo {
 	// cannot be done.
       virtual bool evaluate(int64_t&val) const;
 
+	// This method returns true if the drawn Verilog for this
+	// expression is a primary. A containing expressin can use
+	// this method to know if it needs to wrap parentheses. This
+	// is somewhile optional, so it is better to return false if
+	// not certain. The default implementation does return false.
+      virtual bool is_primary(void) const;
+
 	// Debug dump of the expression.
       virtual void dump(ostream&out, int indent) const =0;
 
@@ -58,6 +65,20 @@ class Expression : public LineInfo {
       Expression& operator = (const Expression&);
 };
 
+class ExpUnary : public Expression {
+
+    public:
+      ExpUnary(Expression*op1);
+      ~ExpUnary();
+
+    protected:
+      int emit_operand1(ostream&out, Entity*ent, Architecture*arc);
+      void dump_operand1(ostream&out, int indent) const;
+
+    private:
+      Expression*operand1_;
+};
+
 /*
  * This is an abstract class that collects some of the common features
  * of binary operators.
@@ -69,10 +90,11 @@ class ExpBinary : public Expression {
       ~ExpBinary();
 
     protected:
-      inline Expression* operand1() { return operand1_; }
-      inline Expression* operand2() { return operand2_; }
-      inline const Expression* operand1() const { return operand1_; }
-      inline const Expression* operand2() const { return operand2_; }
+
+      int emit_operand1(ostream&out, Entity*ent, Architecture*arc);
+      int emit_operand2(ostream&out, Entity*ent, Architecture*arc);
+
+      void dump_operands(ostream&out, int indent) const;
 
     private:
       Expression*operand1_;
@@ -102,6 +124,7 @@ class ExpInteger : public Expression {
       ~ExpInteger();
 
       int emit(ostream&out, Entity*ent, Architecture*arc);
+      bool is_primary(void) const;
       bool evaluate(int64_t&val) const;
       void dump(ostream&out, int indent) const;
 
@@ -136,11 +159,31 @@ class ExpName : public Expression {
       ~ExpName();
 
       int emit(ostream&out, Entity*ent, Architecture*arc);
+      bool is_primary(void) const;
       void dump(ostream&out, int indent) const;
 
     private:
       perm_string name_;
 };
 
+class ExpUAbs : public ExpUnary {
+
+    public:
+      ExpUAbs(Expression*op1);
+      ~ExpUAbs();
+
+      int emit(ostream&out, Entity*ent, Architecture*arc);
+      void dump(ostream&out, int indent) const;
+};
+
+class ExpUNot : public ExpUnary {
+
+    public:
+      ExpUNot(Expression*op1);
+      ~ExpUNot();
+
+      int emit(ostream&out, Entity*ent, Architecture*arc);
+      void dump(ostream&out, int indent) const;
+};
 
 #endif
diff --git a/vhdlpp/expression_emit.cc b/vhdlpp/expression_emit.cc
index 0099fd163..9555a0941 100644
--- a/vhdlpp/expression_emit.cc
+++ b/vhdlpp/expression_emit.cc
@@ -31,11 +31,43 @@ int Expression::emit(ostream&out, Entity*, Architecture*)
       return 1;
 }
 
+bool Expression::is_primary(void) const
+{
+      return false;
+}
+
+int ExpBinary::emit_operand1(ostream&out, Entity*ent, Architecture*arc)
+{
+      int errors = 0;
+      bool oper_primary = operand1_->is_primary();
+      if (! oper_primary) out << "(";
+      errors += operand1_->emit(out, ent, arc);
+      if (! oper_primary) out << ")";
+      return errors;
+}
+
+int ExpBinary::emit_operand2(ostream&out, Entity*ent, Architecture*arc)
+{
+      int errors = 0;
+      bool oper_primary = operand2_->is_primary();
+      if (! oper_primary) out << "(";
+      errors += operand2_->emit(out, ent, arc);
+      if (! oper_primary) out << ")";
+      return errors;
+}
+
+int ExpUnary::emit_operand1(ostream&out, Entity*ent, Architecture*arc)
+{
+      int errors = 0;
+      errors += operand1_->emit(out, ent, arc);
+      return errors;
+}
+
 int ExpArithmetic::emit(ostream&out, Entity*ent, Architecture*arc)
 {
       int errors = 0;
 
-      errors += operand1()->emit(out, ent, arc);
+      errors += emit_operand1(out, ent, arc);
 
       switch (fun_) {
 	  case PLUS:
@@ -61,23 +93,27 @@ int ExpArithmetic::emit(ostream&out, Entity*ent, Architecture*arc)
 	    break;
       }
 
-      errors += operand2()->emit(out, ent, arc);
+      errors += emit_operand2(out, ent, arc);
 
       return errors;
 }
 
 int ExpInteger::emit(ostream&out, Entity*, Architecture*)
 {
-      out << " /* " << get_fileline() << ": internal error: "
-	  << "INTEGER LITERAL */ ";
-      return 1;
+      out << value_;
+      return 0;
+}
+
+bool ExpInteger::is_primary(void) const
+{
+      return true;
 }
 
 int ExpLogical::emit(ostream&out, Entity*ent, Architecture*arc)
 {
       int errors = 0;
 
-      errors += operand1()->emit(out, ent, arc);
+      errors += emit_operand1(out, ent, arc);
 
       switch (fun_) {
 	  case AND:
@@ -100,7 +136,7 @@ int ExpLogical::emit(ostream&out, Entity*ent, Architecture*arc)
 	    break;
       }
 
-      errors += operand2()->emit(out, ent, arc);
+      errors += emit_operand2(out, ent, arc);
 
       return errors;
 }
@@ -112,3 +148,26 @@ int ExpName::emit(ostream&out, Entity*, Architecture*)
       out << name_;
       return errors;
 }
+
+bool ExpName::is_primary(void) const
+{
+      return true;
+}
+
+int ExpUAbs::emit(ostream&out, Entity*ent, Architecture*arc)
+{
+      int errors = 0;
+      out << "abs(";
+      errors += emit_operand1(out, ent, arc);
+      out << ")";
+      return errors;
+}
+
+int ExpUNot::emit(ostream&out, Entity*ent, Architecture*arc)
+{
+      int errors = 0;
+      out << "~(";
+      errors += emit_operand1(out, ent, arc);
+      out << ")";
+      return errors;
+}
diff --git a/vhdlpp/parse.y b/vhdlpp/parse.y
index 079ba521a..5dd1a49f6 100644
--- a/vhdlpp/parse.y
+++ b/vhdlpp/parse.y
@@ -294,6 +294,16 @@ factor
 	FILE_NAME(tmp, @2);
 	$$ = tmp;
       }
+  | K_abs primary
+      { ExpUAbs*tmp = new ExpUAbs($2);
+	FILE_NAME(tmp, @1);
+	$$ = tmp;
+      }
+  | K_not primary
+      { ExpUNot*tmp = new ExpUNot($2);
+	FILE_NAME(tmp, @1);
+	$$ = tmp;
+      }
   ;
 
 identifier_opt : IDENTIFIER { $$ = $1; } |  { $$ = 0; } ;
@@ -384,6 +394,8 @@ primary
 	FILE_NAME(tmp, @1);
 	$$ = tmp;
       }
+  | '(' expression ')'
+      { $$ = $2; }
   ;
 
 relation : shift_expression { $$ = $1; } ;