Zsh: read lines from file into array

#!/bin/zsh
zmodload zsh/mapfile
FNAME=/path/to/some/file.txt
FLINES=( "${(f)mapfile[$FNAME]}" )
LIST="${mapfile[$FNAME]}" # Not required unless stuff uses it
integer POS=1             # Not required unless stuff uses it
integer SIZE=$#FLINES     # Number of lines, not required unless stuff uses it
for ITEM in $FLINES
    # Do stuff
    (( POS++ ))
done

You have some strange things in your code:

1. Why are you splitting LIST each time instead of making it an array variable? It is just a waste of CPU time.
2. Why don’t you use for ITEM in ${(f)LIST}?
3. There is a possibility to directly ask zsh about array length: $#ARRAY. No need in determining the index of the last occurrence of the last element.
4. POS gets the same value as SIZE in your code. Hence it will iterate only once.
5. Brackets are problems likely because of 3.: (I) is matching against a pattern. Do read documentation.

I know it's been a lot of time since the question was answered but I think it's worth posting a simpler answer (which doesn't require the zsh/mapfile external module):

#!/bin/zsh
for line in "${(@f)"$(</path/to/some/file.txt)"}"
{
  // do something with each $line
}