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indexingrebolrebol2

Handling 'none' when trying to find the index? of a value that doesn't exist in Rebol?

I have a block! x: ["one" "two" "three"]

index? find x "two" returns... 2

index? find x "four" returns...

** Script Error: index? expected series argument of type: series port ** Near: index? find x "twos"

What's the best way to have index? return none rather than the error?

Solution 
  • >> help index?
USAGE:
    INDEX? series /xy

DESCRIPTION:
     Returns the index number of the current position in the series.
     INDEX? is an action value.

ARGUMENTS:
     series -- (Type: series port)

REFINEMENTS:
     /xy -- Returns index as an XY pair offset.

    index? expects a series. If the argument is none, it will raise an error. 

    >>  find x "four"
== none

    You can either check if the argument exists or is a series or guard against the error e.g.

    >> if  series? i: find x "four" [index? i]
== none

    or

    >> attempt [index? find x "four" none]
== none