# Create an unnamed m*n array as a table with m rows, each row being a list
create or replace function matrix(m, n, init) as table (
  with recursive row as (
    select list_transform(range(0,n), x -> z) as row
    from (select init as z)),
  cte as (
    select 1 as i, row from row
    union all
    select i+1, row
    from cte
    where i < m
  )
  from cte
);

# The backing table
create or replace table t_ (
  i INTEGER NOT NULL check(i>0), check(i<= getenv('M')::INTEGER),
  row DOUBLE[]
);

# The view
create or replace view t as from t_ order by i;

# Initialize the backing table
insert into t_ from matrix( getvariable('M')::INT, getvariable('N')::INT, 0.0);

prepare update_matrix as /* $1=i $2=j $3=value */
update t_
  set row = row[1:$2-1] || [$3] || row[$2+1:]
  where i =  $1
;

create or replace function matrix_get(ii,jj) as (
  select row[jj]
  from t
  where i = ii
  );