function
boot.janet on line 1337 , column 1
(index-of val x &opt dflt )
Find the first key associated with a value `val` in `x` , acting
like a reverse lookup. Will not look at dictionary prototypes. If
not found , return `dflt` if given , or `nil` otherwise.
`x` can be a bytes , indexed , dictionary , fiber , or abstract type
with suitable `get` and `next` methods.
# in struct
(index-of 2 {:a 1 :b 2 :c 3 :d 2 } )
# => :b
# in table
(index-of 2 @{:a 1 :b 2 :c 3 :d 2 })
# => :b
# in array
(index-of 6 @[4 5 6 7 8 9 ] )
# => 2
# in tuple
(index-of 2 [1 2 3 4 ])
# => 1