volume level widget crash

[retroj]

This is an error with a widget in my own config, but I'm filing it here so I will remember to come back to it.

Here is the widget:

;; volume
;;

(define (alsa-volume-get-volume)
  (let loop ((lines (with-input-from-pipe
                     "amixer sget Master,0"
                     read-lines)))
    (if (null? lines)
        #f
        (let ((m (string-match
                  '(: (* any) "[" ($ (+ num)) "%] ["
                      ($ (+ alpha)) "]")
                  (first lines))))
          (if m
              (list (string->number (second m))
                    (if (equal? "off" (third m)) #f #t))
              (loop (rest lines)))))))

(define alsa-volume-format
  (match-lambda
    (#f "")
    ((? string? text) text)
    ((level #f) '(color (1 0 0 1) "MUTE"))
    ((level #t)
     (let* ((indicator "▁▂▄▆█")
            (indicator-length (string-length indicator))
            (n (inexact->exact (floor (* (min 100 level) 0.01 indicator-length)))))
       `(color (0.5 0.5 1 1)
               (font "DejaVu Sans Mono-8:bold"
                     ,(string-pad-right (substring indicator 0 n) indicator-length))
               ,(->string level))))))

(define (widget:alsa-volume)
  (widget:text
   format: alsa-volume-format
   init: (lambda (widget)
           (thread-start!
            (lambda ()
              (call-with-input-pipe
               "stdbuf -oL alsactl monitor"
               (lambda (port)
                 (let ((fileno (port->fileno port)))
                   (let loop ()
                     (thread-wait-for-i/o! fileno input:)
                     (read-line port)
                     (update widget (alsa-volume-get-volume))
                     (loop)))))))
           (update widget (alsa-volume-get-volume)))))

Here is the error. Not sure about steps to reproduce:

Warning (#<thread: thread1753>): in thread: (>) bad argument type: (color (0.5 0.5 1 1) (font "DejaVu Sans Mono-8:bold" "▁▂▄▆ ") "89")

        Call history:

        mowedline.scm:338: max          <--