Array operator "sum array values"

Hi,

is there a syntax that sums the values of an array?

That is, having an array like

{1,3,8},{5,6,7}

something like

select arr[1:2][2:3]

gives

{1,3},{6,7}


; what I'd like is:

select arr[1$2][2$3]

gives:

17 (that is, 1+3 + 6+7)

If there is no such operator, would it be complicated adding it to postgres?
I mean: is the "[:]" operator an internal thing (the parser "knows" about it) or is it just like any other operators
thatcan be added ? 









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