Fun with Macros: With-EOF-Handled
Posted on June 23rd, 2024.
It's been a while (again), but it's time to take a look at another little Common
Lisp macro that I find myself using fairly often: with-eof-handled.
Usage
Common Lisp has several functions for reading from character streams, e.g.
read-char and read-line. The arguments for these functions follow a common
pattern where they take (&optional input-stream eof-error-p eof-value) (and
one more argument that's not relevant here). By default, calling one of these
functions will signal an error if an end of file occurs. You can change this by
passing true as the eof-error-p argument (which, despite its -p suffix
should be a (generalized) boolean, not a predicate), in which case the
eof-value will be returned instead of signaling an error.