this one hangs after about 5 minutes:
$ csi -s geojson-generator.scm | csi -s ./arp-boats.scm -:g -:hm16M 2>&1 | grep resize -C 5



;; boat service:
(use matchable cjson srfi-18)

;; workaround for blocking on i/o when reading json from stdin
(include "nonblocking-input-ports.scm")
(current-input-port (open-input-file*/nonblock 0))

;; ==================== debug

(thread-start! (lambda () (use nrepl) (nrepl 1234)))


;; ==================== globals

(define state '())

;; ==================== boat utils

(define (geojson-mmsi geojson)
  (let ((mmsi (alist-ref 'mmsi (or (alist-ref 'properties geojson) '()))))
    (assert (number? mmsi))
    mmsi))

;; (pp (extract (include "./boat.data.scm")))

;; input: alist ((pos . (lat . lon)) (mmsi . mmsi))
;; state is a map of <mmsi>:<properties>
(define (prj-geojson geojson state)
  (assert (<= (length state) 20000))
  ;; set properties for mmsi key:
  (alist-update (geojson-mmsi geojson) ;; key (mmsi)
                geojson ;; value (geojson feature)
                state))

(define count 0)
(port-for-each
 (lambda (line)
   (let ((json (string->json line)))
     (set! count (add1 count))
     (set! state (prj-geojson json state))))
 read-line)