Use the appropriate monospace font per OS

tm/gui.rkt

@@ -8,16 +8,25 @@
 (provide run-simulation
          simulate)
 
+;query what monospace font to use depending on the OS
+(define (get-monospace-font)
+  (match (system-type 'os)
+    ['windows "Consolas"]
+    ['unix    "Noto Sans Mono"]
+    ['macosx  "Menlo"]))
+
 (define (tape-cell i sym [head? #f])
   (above/align
    "middle"
    (text/font (number->string i)
                12 "gray"
-               #f "modern" "normal" "normal" #f)
+               (get-monospace-font)
+               "modern" "normal" "normal" #f)
    (overlay
     (text/font (if (eq? sym BLANK) "" (string sym))
                30 "black"
-               #f "modern" "normal" "normal" #f)
+               (get-monospace-font)
+               "modern" "normal" "normal" #f)
     (square 40 "outline" "black")
     (square 40 "solid" (make-color 239 239 239)))
    (if head? tape-head no-tape-head)))
@@ -40,7 +49,7 @@
   (overlay/align "left" "middle"
    (text/font linestr
               18 "black"
-              #f ;"JuliaMono"
+              (get-monospace-font)
               "modern" "normal" "normal" #f)
    (rectangle (* TAPE-WIDTH 40) 30 "solid"
               (if in-focus?