truename

(truename pathname)

Returns the pathname when the file exists and signals an error when it does not. The signal is the point: (ignore-errors (truename path)) is the Common Lisp idiom for "this path if it is there, nil otherwise", and libraries use it to probe for an optional file or directory.

rontolisp resolves no symbolic links and makes nothing absolute, so the value on success is a pathname carrying the argument namestring. When you want the answer without the condition, use probe-file, which asks the same question and returns nil instead of signalling.

Backend support

Works on all four backends: one definition in rontolisp source over probe-file, spliced into the program when it is referenced.