astAssignmentExpression(assNode, retArr) {
    const declaration = this.getDeclaration(assNode.left);
    if (declaration && !declaration.assignable) {
      throw this.astErrorOutput(`Variable ${assNode.left.name} is not assignable here`, assNode);
    }
    this.astGeneric(assNode.left, retArr);
    retArr.push(assNode.operator);
    this.astGeneric(assNode.right, retArr);
    return retArr;
  }
@desc Parses the abstract syntax tree for *Assignment* Expression
@param {Object} assNode - An ast Node
@param {Array} retArr - return array string
@returns {Array} the append retArr