Handle NULL result from read_expression() in REPL

lib/repl.c

@@ -1,6 +1,7 @@
 #include "repl.h"
 
 #include <stdio.h>
+#include <string.h>
 
 void init_repl(repl_t *repl)
 {
@@ -19,6 +20,12 @@ bool step_repl(repl_t *repl)
 		repl->line_buffer[len] = (char)byte;
 	}
 	const expression_t *e = repl->read(&repl->pool, repl->line_buffer, len);
+	if (NULL == e) {
+		const char *msg = "Invalid expression\n";
+		repl->print(msg, strlen(msg));
+		return true;
+	}
+
 	const int result = repl->evaluate(e);
 	const int result_len = snprintf(
 	    repl->result_buffer, REPL_RESULT_BUFFER_SIZE, "%d\n", result);