Re: Constraint: string length must be 32 chars

snake=> create table gps (
id varchar(32) primary key CONSTRAINT id_length char_length(id)=32,
stamp timestamp DEFAULT current_timestamp,
pos point);
ERROR: syntax error at or near "char_length"
LINE 2: id varchar(32) primary key CONSTRAINT id_length char_length(...
^

snake=> create table gps (
id varchar(32) primary key CHECK id_length char_length(id)=32,
stamp timestamp DEFAULT current_timestamp,
pos point);
ERROR: syntax error at or near "id_length"
LINE 2: id varchar(32) primary key CHECK id_length char_length(id)=3...
^

snake=> create table gps (
id varchar(32) primary key CHECK char_length(id)=32,
stamp timestamp DEFAULT current_timestamp,
pos point);
ERROR: syntax error at or near "char_length"
LINE 2: id varchar(32) primary key CHECK char_length(id)=32,
^

Sorry, any ideas? (I know it's a stupid question)
Alex