A little piece of code which uses two closures, partial application and a higher order function. The poor perl code reflects my few weeks on this language. 
# getRowsLazy :: DB_Handle -> (String -> String -> ()) -> (SQLQuery ->
+ {':parm1' => value, ...} -> [[DBType, ..., DBType]])
# Closure on $dbh, lazy version and partial application on the first t
+wo params
# 
# ex: my $dbh = ...DBI connect...
      my $getRows = F::getRowsLazy($dbh, sub { myErrFun($[0], $[1], $M
+Y_FUN_NAME, $MY_TRACE_LEVEL) } );
#     ...
#     my $iter = $getRows->("select * from device_param where ID=:id",
+ {':id' => 123456});
#     while (my $row = $iter->()) {
#       print $row->[0] . ", " . $row->[1] . "\n";
#     }
#
sub F::getRowsLazy {
  my ($dbh, $errFun);
  return sub {
    my ($sql,$p) = @_;
    my $sth = $dbh->prepare($sql) || $errFun->("Error in DBI::prepare"
+, $dbh->errstr() );
    
    while (my ($k,$v) = each(%$p)) {$sth->bind_param($k, $v);}
    
    $sth->execute() || $errFun->("Error in DBI::execute", $dbh->errstr
+() );
    
    my $yield = sub {
      my $row = $sth->fetchrow_arrayref;
      if ($row) {return $row;}
      $sth->finish();
      return undef;
    };
    
    return $yield;         # the call to $yield->() returns a referenc
+e; doesn't work with array, but I don't know way
  }
};

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In reply to Re: understanding closures by enriirne
in thread understanding closures by reasonablekeith

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