1 files changed, 7 insertions, 1 deletions
diff --git a/chapter25/src/main/smp/sys/Scan.smp b/chapter25/src/main/smp/sys/Scan.smp
index acf366f7..acf9fbb8 100644
--- a/chapter25/src/main/smp/sys/Scan.smp
+++ b/chapter25/src/main/smp/sys/Scan.smp
@@ -3,6 +3,7 @@
 // Scanner; a simple string parser.
 struct Scan {
     int !x;                     // Cursor
+    bool !bad;                  // True after a malformed token
     u8[~] buf;                  // Immutable byte array, must be set in 2nd constructor
 
     new Scan = { u8[~] b ->
@@ -19,6 +20,7 @@ struct Scan {
     // True if find required character, and skip it; else False.
     val match = { u8 c ->
         skip();
+        if( x >= buf# ) return false;
         if( buf[x] != c ) return false;
         x++;
         return true;
@@ -28,8 +30,12 @@ struct Scan {
     val number = { ->
         skip();
         bool neg = match('-');
+        if( x >= buf# || buf[x] < '0' || '9' < buf[x] ) {
+            bad = true;
+            return 0;
+        }
         i64 n = 0;
-        while( '0' <= buf[x] & buf[x] <= '9' )
+        while( x < buf# && '0' <= buf[x] & buf[x] <= '9' )
             n = n*10 + (buf[x++] - '0');
         return neg ? -n : n;
     };