Marc: After spending 15 minutes or so trying to interpret the cryptic and incomplete error message

(define g (pgm->f64 (read-pgm "circle-128.pgm"))) *** ERROR IN read-pgm, "../pgm.scm"@36.3 -- (Argument 1) STRING or port settings expected (call-with-input-file '(path: "circle-128.pgm" char-encoding: latin1 eol-encoding: lf) '#<procedure #2>)

I discovered that you removed latin1 as a valid char-encoding. Perhaps you should mention this in the documentation. (I suppose a more helpful error message may work, too.) Brad