OpenEuphoria

Can someone explain vslice()'s error_control to me?

• Posted by petelomax Oct 23, 2014
• 1236 views

I am assuming that someone saw aku's version from 2005:

global function vslice(sequence s, atom colno) 
sequence ret 
    ret = {} 
    for i = 1 to length(s) do 
        ret = append(ret, s[i][colno]) 
    end for 
    return ret 
end function 

and thought they'd "enhance" it.

public function vslice(sequence source, atom colno, object error_control=0) 
sequence ret 
integer substitutes, current_sub 
 
    if colno<1 then 
        crash("sequence:vslice(): colno should be a valid index, but was %d",colno) 
    end if 
 
    ret = source 
    if atom(error_control) then 
        substitutes = -(not error_control) 
    else 
        substitutes = length(error_control) 
        current_sub = 1 
    end if 
 
    for i=1 to length(source) do 
        if colno>=1+length(source[i]) then 
            if substitutes=-1 then 
                crash("sequence:vslice(): colno should be a valid index on the %d-th element, but was %d", {i,colno}) 
            elsif substitutes=0 then 
                return ret[1..i-1] 
            else 
                substitutes -= 1 
                ret[i] = error_control[current_sub] 
                current_sub += 1 
            end if 
        else 
            ret[i] = source[i][colno] 
        end if 
    end for 
 
    return ret 
end function 

I understand missing columns => crash, as the default behaviour and personally I'd have left it at that.
I don't get why anyone might want a short slice, an example of that being useful for something might help.
I certainly don't get why anyone would want to interpolate successive elements of error_control within/as substitutes for missing elements of source, and potentially get a partially-short slice back, and I guess that you are expected to test length(res)=length(source) to figure out whether the latter happened. Or is one expected to pass repeat(default,length(source)) to error_control to ensure logical behaviour?

Pete