First commit

exercises/ch04/ex4_8.lua

@@ -0,0 +1,39 @@
+local function remove(str, start, _end)
+    local start_part = str:sub(1, start - 1)
+    local end_part = str:sub(_end + 1, -1)
+    return start_part .. end_part
+end
+
+local function remove_patterns(str, pattern)
+    while true do
+        local rem_start, rem_end, _ = str:find(pattern)
+        if rem_start == nil then
+            break
+        end
+        str = remove(str, rem_start, rem_end)
+    end
+
+    return str
+end
+
+local function ispali(str)
+    str = str:lower()
+
+    -- format
+    str = remove_patterns(str, "%s")
+    str = remove_patterns(str, "%p")
+
+    return str == str:reverse()
+end
+
+local function test(str)
+    print(("%s: %q"):format(str, ispali(str)))
+end
+
+test("step on no pets")
+test("banana")
+
+print()
+
+test("Step. On no   pets!")
+test("Banana??")