diff --git a/OperatorToken.go b/OperatorToken.go
index c9e4365..c96eb8d 100644
--- a/OperatorToken.go
+++ b/OperatorToken.go
@@ -39,12 +39,16 @@ const (
 	TERNARY_TRUE
 	TERNARY_FALSE
 	COALESCE
+
+	// as distinct from the TokenKind.
+	FUNCTION_OPERATOR
 )
 
 type OperatorPrecedence int
 
 const (
 	VALUE_PRECEDENCE OperatorPrecedence = iota
+	FUNCTION_PRECEDENCE
 	PREFIX_PRECEDENCE
 	EXPONENTIAL_PRECEDENCE
 	ADDITIVE_PRECEDENCE
@@ -113,9 +117,11 @@ func findOperatorPrecedenceForSymbol(symbol OperatorSymbol) OperatorPrecedence {
 		fallthrough
 	case TERNARY_FALSE:
 		return TERNARY_PRECEDENCE
+	case FUNCTION_OPERATOR:
+		return FUNCTION_PRECEDENCE
 	}
 
-	return -1
+	return VALUE_PRECEDENCE
 }
 
 /*
diff --git a/evaluationStage.go b/evaluationStage.go
index d033ee4..a02012f 100644
--- a/evaluationStage.go
+++ b/evaluationStage.go
@@ -193,7 +193,17 @@ func makeFunctionStage(function ExpressionFunction) evaluationOperator {
 
 	return func(left interface{}, right interface{}, parameters Parameters) (interface{}, error) {
 
-		return function(right.([]interface{})...)
+		if(right == nil) {
+			return function()
+		}
+
+		switch right.(type) {
+		case []interface{}:
+			return function(right.([]interface{})...)
+		default:
+			return function(right)
+		}
+
 	}
 }
 
diff --git a/evaluation_test.go b/evaluation_test.go
index 41c0ba4..42e6081 100644
--- a/evaluation_test.go
+++ b/evaluation_test.go
@@ -12,6 +12,7 @@ import (
 type EvaluationTest struct {
 	Name       string
 	Input      string
+	Functions map[string]ExpressionFunction
 	Parameters []EvaluationParameter
 	Expected   interface{}
 }
@@ -448,6 +449,31 @@ func TestNoParameterEvaluation(test *testing.T) {
 			Input:    "1 ?? 2",
 			Expected: 1.0,
 		},
+		EvaluationTest{
+
+			Name:	"Single function",
+			Input:	"foo()",
+			Functions: map[string]ExpressionFunction {
+				"foo": func(arguments ...interface{}) (interface{}, error) {
+					return true, nil
+				},
+			},
+
+			Expected: true,
+		},
+		EvaluationTest{
+
+			Name:	"Function with argument",
+			Input:	"passthrough(1)",
+			Functions: map[string]ExpressionFunction {
+				"passthrough": func(arguments ...interface{}) (interface{}, error) {
+					fmt.Printf("Arg zero: %v\n", arguments)
+					return arguments[0], nil
+				},
+			},
+
+			Expected: 1.0,
+		},
 	}
 
 	runEvaluationTests(evaluationTests, test)
@@ -898,7 +924,11 @@ func runEvaluationTests(evaluationTests []EvaluationTest, test *testing.T) {
 	// Run the test cases.
 	for _, evaluationTest := range evaluationTests {
 
-		expression, err = NewEvaluableExpression(evaluationTest.Input)
+		if(evaluationTest.Functions != nil) {
+			expression, err = NewEvaluableExpressionWithFunctions(evaluationTest.Input, evaluationTest.Functions)
+		} else {
+			expression, err = NewEvaluableExpression(evaluationTest.Input)
+		}
 
 		if err != nil {
 
diff --git a/stagePlanner.go b/stagePlanner.go
index 9454100..ce5401c 100644
--- a/stagePlanner.go
+++ b/stagePlanner.go
@@ -95,6 +95,7 @@ var planShift precedent
 var planComparator precedent
 var planLogical precedent
 var planTernary precedent
+var planSeparator precedent
 
 func init() {
 
@@ -105,13 +106,13 @@ func init() {
 		validSymbols:    PREFIX_SYMBOLS,
 		validKinds:		 []TokenKind {PREFIX},
 		typeErrorFormat: TYPEERROR_PREFIX,
-		nextRight:       planValue,
+		nextRight:       planFunction,
 	})
 	planExponential = makePrecedentFromPlanner(&precedencePlanner{
 		validSymbols:    EXPONENTIAL_SYMBOLS,
 		validKinds:		 []TokenKind {MODIFIER},
 		typeErrorFormat: TYPEERROR_MODIFIER,
-		next:            planValue,
+		next:            planFunction,
 	})
 	planMultiplicative = makePrecedentFromPlanner(&precedencePlanner{
 		validSymbols:    MULTIPLICATIVE_SYMBOLS,
@@ -155,6 +156,10 @@ func init() {
 		typeErrorFormat: TYPEERROR_TERNARY,
 		next:            planLogical,
 	})
+	planSeparator = makePrecedentFromPlanner(&precedencePlanner{
+		validKinds:		[]TokenKind {SEPARATOR},
+		next: planTernary,
+	})
 }
 
 /*
@@ -183,7 +188,7 @@ func planTokens(stream *tokenStream) (*evaluationStage, error) {
 		return nil, nil
 	}
 
-	return planTernary(stream)
+	return planSeparator(stream)
 }
 
 /*
@@ -206,6 +211,7 @@ func planPrecedenceLevel(
 	var keyFound bool
 
 	if leftPrecedent != nil {
+
 		leftStage, err = leftPrecedent(stream)
 		if err != nil {
 			return nil, err
@@ -215,9 +221,6 @@ func planPrecedenceLevel(
 	for stream.hasNext() {
 
 		token = stream.next()
-		if !isString(token.Value) {
-			break
-		}
 
 		if(len(validKinds) > 0) {
 
@@ -233,9 +236,17 @@ func planPrecedenceLevel(
 				break
 			}
 		}
-		symbol, keyFound = validSymbols[token.Value.(string)]
-		if !keyFound {
-			break
+
+		if(validSymbols != nil) {
+
+			if(!isString(token.Value)) {
+				break;
+			}
+
+			symbol, keyFound = validSymbols[token.Value.(string)]
+			if !keyFound {
+				break
+			}
 		}
 
 		if rightPrecedent != nil {
@@ -367,6 +378,36 @@ func findTypeChecks(symbol OperatorSymbol) typeChecks {
 	}
 }
 
+/*
+	A special case where functions need to be of higher precedence than values, and need a special wrapped execution stage operator.
+*/
+func planFunction(stream *tokenStream) (*evaluationStage, error) {
+
+	var token ExpressionToken
+	var rightStage *evaluationStage
+	var err error
+
+	token = stream.next()
+
+	if(token.Kind != FUNCTION) {
+		stream.rewind()
+		return planValue(stream)
+	}
+
+	rightStage, err = planValue(stream)
+	if err != nil {
+		return nil, err
+	}
+
+	return &evaluationStage{
+
+		symbol: FUNCTION_OPERATOR,
+		rightStage: rightStage,
+		operator:   makeFunctionStage(token.Value.(ExpressionFunction)),
+		typeErrorFormat: "Unable to run function '%v': %v",
+	}, nil
+}
+
 /*
 	A truly special precedence function, this handles all the "lowest-case" errata of the process, including literals, parmeters,
 	clauses, and prefixes.
@@ -392,13 +433,13 @@ func planValue(stream *tokenStream) (*evaluationStage, error) {
 		// advance past the CLAUSE_CLOSE token. We know that it's a CLAUSE_CLOSE, because at parse-time we check for unbalanced parens.
 		stream.next()
 		return ret, nil
+		
+	case CLAUSE_CLOSE:
+		return planTokens(stream)
 
 	case VARIABLE:
 		operator = makeParameterStage(token.Value.(string))
 
-	case FUNCTION:
-		operator = makeFunctionStage(token.Value.(ExpressionFunction))
-
 	case NUMERIC:
 		fallthrough
 	case STRING: