doc: sample: add a slightly more complicated block sample

diag/write/pretty.c

@@ -4,10 +4,10 @@
 #include "../write.h"
 
 #include <assert.h>
+#include <ctype.h>
 #include <fx/core/stringstream.h>
 #include <fx/term/print.h>
 #include <fx/term/tty.h>
-#include <ctype.h>
 #include <ivy/line-source.h>
 #include <stdlib.h>
 
@@ -449,11 +449,15 @@ static void print_snippet(
 			update_highlighting(&printer);
 
 			diag_stream_putc(stream, c);
+			if (c == '[') {
+				diag_stream_putc(stream, c);
+			}
 
 			update_underline(&printer);
 		}
 
 		diag_stream_putc(stream, '\n');
+
 		write_underline(&printer);
 	}
 }

doc/sample/Simple.im

@@ -6,4 +6,6 @@ y = 32 * 64.
 z = 64 / 4.
 x = y + z.
 
+q = [ x = y[0] ].
+
 cout put:'Answer: {x}'