Allow constant and variable definitions via grouping syntax (#41)

Author: monstermichl

README.md

@@ -30,20 +30,28 @@ Supported variable types are *bool*, *int*, *string* and *error*.
 ```golang
 // Variable definition with default value.
 var a int
-var a, b int
+var b, c int
 ```
 
 ```golang
 // Variable definition with assigned value.
 var a int = 5
-var a, b int = divisionWithRemainder(5, 2)
+var b, c int = divisionWithRemainder(5, 2)
+```
+
+```golang
+// Variable definition via grouping.
+var (
+    a = 5
+    b, c int = divisionWithRemainder(5, 2)
+)
 ```
 
 ```golang
 // Variable definition short form.
 a := 5
-a, b := 5, 6
-a, b := divisionWithRemainder(5, 2)
+b, c := 5, 6
+d, e := divisionWithRemainder(5, 2)
 ```
 
 ### Control flow

parser/assignment.go

@@ -0,0 +1,6 @@
+package parser
+
+type Assignment interface {
+	Statement
+	AssignmentType() AssignmentType
+}

parser/const.go

@@ -49,6 +49,10 @@ func (c ConstDefinition) StatementType() StatementType {
 	return STATEMENT_TYPE_CONST_DEFINITION
 }
 
+func (c ConstDefinition) AssignmentType() AssignmentType {
+	return ASSIGNMENT_TYPE_VALUE
+}
+
 func (c ConstDefinition) Constants() []Const {
 	return c.constants
 }

parser/namedvalue.go

@@ -7,3 +7,19 @@ type NamedValue interface {
 	Public() bool
 	IsConstant() bool
 }
+
+type NamedValuesDefinition struct {
+	assignments []Assignment
+}
+
+func (v NamedValuesDefinition) StatementType() StatementType {
+	return STATEMENT_TYPE_NAMED_VALUES_DEFINITION
+}
+
+func (v *NamedValuesDefinition) AddAssignment(assignment Assignment) {
+	v.assignments = append(v.assignments, assignment)
+}
+
+func (v NamedValuesDefinition) Assignments() []Assignment {
+	return v.assignments
+}