Altering field passed as parameter to plpgsql trigger

[Steve Crawford <scrawford@xxxxxxxxxxxxxxxxxxxx>]

I am trying to make a function that can be reused as a trigger on 
various tables but am somehow not finding the correct syntax for using a 
parameter to the function to identify the column to be altered by the 
trigger. Stripped to basics:

create or replace function foo_trigger()
returns trigger
as '
declare
 ...
begin
 trigger_table = TG_ARGV[0];
 field_to_alter = TG_ARGV[1];
 ...
 new.field_to_alter = some_computed_value;  <<==========
 return new;
end;'
language 'plpgsql';

create trigger foo_change before insert on foo
 for each row execute procedure foo_trigger('foo','somealteredfield');

What is the correct syntax for the line:
new.field_to_alter = some_computed_value;

Also, does plpgsql have a preferred way to identify the table that fired 
the trigger. I see the syntax for C but not for plpgsql.

Cheers,
Steve


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