Adding new syntax in postgre sql

I am new to postgre sql .And i want to add some new feature to postgresql
As a startup i have taken the project to add syntax for table partitioning

CREATE TABLE is modified to accept a PARTITION BY clause. This clause
contains one or more partition declarations. The syntax is as follows:

PARTITION BY {partition_type} (column_name[, column_name...])
[PARTITIONS number]
(
partition_declaration[, partition_declaration...]

)

The partition type can be one of HASH, RANGE or LIST.

so can anyone tell me from where to start .
I have read all the basics
but i dont know the control flow for adding new syntax.

so please tell me how to add new syntax
from parser to executor..