Tweak guard; small demo

ansi/lcd-terminal.rkt

@@ -126,7 +126,8 @@
     ["c" (S- 'right)]
     ["d" (S- 'left)]
     ["h" #:when (equal? params '(4)) (simple-key 'insert)] ;; st, http://st.suckless.org/
-    ["t" #:when (equal? (car params) 8) (apply screen-size-report (cdr params))]
+    ["t" #:when (and (= (length params) 3) (= (car params) 8))
+         (apply screen-size-report (cdr params))]
     [_ (simple-key (unknown-escape-sequence lexeme))]))
 
 (define (analyze-vt-O-mainchar lexeme mainchar)

ansi/test-screen-size.rkt

@@ -0,0 +1,24 @@
+#lang racket/base
+
+(require "main.rkt")
+
+(define (display* . things)
+  (for-each display things)
+  (flush-output))
+
+(define (main)
+  (tty-raw!)
+
+  (display* (dec-soft-terminal-reset)
+            (device-request-screen-size))
+
+  (define report (lex-lcd-input (current-input-port)))
+  (printf "The reported screen size is ~a columns and ~a rows.\r\n"
+          (screen-size-report-columns report)
+          (screen-size-report-rows report))
+  (printf "The raw report value itself is ~v.\r\n" report)
+
+  (display* (dec-soft-terminal-reset)))
+
+(module+ main
+  (main))