LATERAL query extreme slow due to partition

[Tom Smith <tomsmith1989sk@xxxxxxxxx>]

Hi:

I am using the wonderful  lateral query  feature like the following

select * from generate_series (1,100000,5) T(t),
   lateral (select * from P where t between  t and t +  3)

P is a parent table of a hundred partitions

the idea is to for each t value from 1 to 100000 with step of 5,

get rows from P (in one or two of its partitions) that  between 

the current value of t and t+3,

so each lateral select should only index scan one or two partitons

but the query plan shows that each will scan all hundred paritions,

I think due to its unable to determine the range since

the query is select * from P where t between  t and t +  3 

as "t" is unknown at the time of parsing.

How to force query planner "dynamically" generate plan to

for each lateral select query as "t" changes.

Thanks