How can I fix 'noun result was required' error in J?

Question

I'm trying to do the 4th Advent of Code problem using J, and I've ran into lots of problems, but now I have a code that looks like this:

fn =. < 'D:/PyCharm/AOC/output4.txt'
data =. freads fn
concatIntegers  =. ,&'x'@,&.":


separado =.  ;: data
lista =. > ((i.(#separado)%2)*2) {separado

n_lista =. #lista 
n_2 =. n_lista % 4

lista_2 =. concatIntegers each/|:lista
matriz =. 250 4 $ > lista_2

loop =: monad : 0
res =. 0
i=.0
condicion=.0
for_i. i.250 do.
    fila =. i { matriz
    elfo11 =. 0 {fila
    elfo12 =. 1 {fila
    elfo21 =. 2 {fila
    elfo22 =. 3 {fila 
    condicion =. ((elfo11 <: elfo21) *. (elfo12 >: elfo22)) +. ((elfo21 <: elfo11) *. (elfo22 >: elfo12))
    if. condicion do.
      res =. >: res
    end.
end.
res
)

loop matriz

What this should do is: Loads a txt file, parses it, creates a matrix, and then using the verb loop it would add 1 to a counter every time the condition is applied.

The thing is, I can't make that loop work, every time I try running it, it gives me the same error:

|noun result was required: loop
|       condicion
|[-30] d:\pycharm\aoc\day4.ijs

I am losing my mind

The code works until it reaches the loop verb I created, but I've been looking through documentation for ages and I can't spot my error

The code until that works as intended

Answer 1

Problem #1: variable i used in:
fila =. i { matriz
is not defined and is considered as unknown verb not noun.

Problem #2: loop iterates on martiz which is of lenght 250 elements (each element is list of 4 integers). But it does 1000 iterations, so there is out of array bound here.

Try to replace the line:
for. i.1000 do.
by the line
for_i. i.250 do.

Problem #3: there is no priorities for operators, so condition should be computed as (I guess here):
condicion =. ((elfo11 <: elfo21) *. (elfo12 >: elfo22)) +. ((elfo21 <: elfo11) *. (elfo22 >: elfo12))

Problem #4: res increment is not saved, try to replace the line:
>: res
by the line
res=. >: res

Problem #5: loop verb cannot see martiz noun since that is local, try to replace the line:
matriz =. 250 4 $ > lista_2
by the line
matriz =: 250 4 $ > lista_2