diff --git a/src/kemal.cr b/src/kemal.cr
index 54c6592..575ff30 100644
--- a/src/kemal.cr
+++ b/src/kemal.cr
@@ -68,15 +68,12 @@ module Kemal
   end
 
   def self.stop
-    if config.running
-      if server = config.server
-        server.close unless server.closed?
-        config.running = false
-      else
-        raise "Kemal.config.server is not set. Please use Kemal.run to set the server."
-      end
+    raise "Kemal is already stopped." if !config.running
+    if server = config.server
+      server.close unless server.closed?
+      config.running = false
     else
-      raise "Kemal is already stopped."
+      raise "Kemal.config.server is not set. Please use Kemal.run to set the server."
     end
   end
 
diff --git a/src/kemal/cli.cr b/src/kemal/cli.cr
index 86dd8cf..56c92f0 100644
--- a/src/kemal/cli.cr
+++ b/src/kemal/cli.cr
@@ -41,14 +41,8 @@ module Kemal
     private def configure_ssl
       {% if !flag?(:without_openssl) %}
       if @ssl_enabled
-        unless @key_file
-          puts "SSL Key Not Found"
-          exit
-        end
-        unless @cert_file
-          puts "SSL Certificate Not Found"
-          exit
-        end
+        abort "SSL Key Not Found" if !@key_file
+        abort "SSL Certificate Not Found" if !@cert_file
         ssl = Kemal::SSL.new
         ssl.key_file = @key_file.not_nil!
         ssl.cert_file =  @cert_file.not_nil!
@@ -58,7 +52,9 @@ module Kemal
     end
 
     private def read_env
-      @config.env = ENV["KEMAL_ENV"] if ENV.has_key?("KEMAL_ENV")
+      if kemal_env = ENV["KEMAL_ENV"]?
+        @config.env = kemal_env
+      end
     end
   end
 end
diff --git a/src/kemal/config.cr b/src/kemal/config.cr
index 508ec36..04bbdd7 100644
--- a/src/kemal/config.cr
+++ b/src/kemal/config.cr
@@ -144,15 +144,10 @@ module Kemal
     end
 
     private def setup_custom_handlers
-      CUSTOM_HANDLERS.each do |ch|
-        position = ch[0]
-        if !position
-          HANDLERS.insert(@handler_position, ch[1])
-          @handler_position += 1
-        else
-          HANDLERS.insert(position, ch[1])
-          @handler_position += 1
-        end
+      CUSTOM_HANDLERS.each do |ch0, ch1|
+        position = ch0
+        HANDLERS.insert (position || @handler_position), ch1
+        @handler_position += 1
       end
     end
 
diff --git a/src/kemal/filter_handler.cr b/src/kemal/filter_handler.cr
index 38b84fe..6d28680 100644
--- a/src/kemal/filter_handler.cr
+++ b/src/kemal/filter_handler.cr
@@ -30,7 +30,7 @@ module Kemal
     def _add_route_filter(verb : String, path, type, &block : HTTP::Server::Context -> _)
       lookup = lookup_filters_for_path_type(verb, path, type)
       if lookup.found? && lookup.payload.is_a?(Array(FilterBlock))
-        (lookup.payload.as(Array(FilterBlock))) << FilterBlock.new(&block)
+        lookup.payload << FilterBlock.new(&block)
       else
         @tree.add radix_path(verb, path, type), [FilterBlock.new(&block)]
       end
@@ -54,8 +54,8 @@ module Kemal
     private def call_block_for_path_type(verb : String?, path : String, type, context : HTTP::Server::Context)
       lookup = lookup_filters_for_path_type(verb, path, type)
       if lookup.found? && lookup.payload.is_a? Array(FilterBlock)
-        blocks = lookup.payload.as(Array(FilterBlock))
-        blocks.each { |block| block.call(context) }
+        blocks = lookup.payload
+        blocks.each &.call(context)
       end
     end
 
diff --git a/src/kemal/handler.cr b/src/kemal/handler.cr
index cae01b5..83ddc6f 100644
--- a/src/kemal/handler.cr
+++ b/src/kemal/handler.cr
@@ -11,15 +11,17 @@ module Kemal
 
     macro only(paths, method = "GET")
       class_name = {{@type.name}}
+      method_downcase = {{method}}.downcase
+      class_name_method = "#{class_name}/#{method_downcase}"
       ({{paths}}).each do |path|
-        @@only_routes_tree.add "#{class_name}/#{{{method}}.downcase}#{path}", "/#{{{method}}.downcase}#{path}"
+        @@only_routes_tree.add class_name_method + path, '/' + method_downcase + path
       end
     end
 
     macro exclude(paths, method = "GET")
       class_name = {{@type.name}}
       ({{paths}}).each do |path|
-        @@exclude_routes_tree.add "#{class_name}/#{{{method}}.downcase}#{path}", "/#{{{method}}.downcase}#{path}"
+        @@exclude_routes_tree.add class_name_method + path, '/' + method_downcase + path
       end
     end
 
diff --git a/src/kemal/helpers/helpers.cr b/src/kemal/helpers/helpers.cr
index 3ed4045..f487c99 100644
--- a/src/kemal/helpers/helpers.cr
+++ b/src/kemal/helpers/helpers.cr
@@ -127,12 +127,14 @@ def send_file(env : HTTP::Server::Context, path : String, mime_type : String? =
     if env.request.method == "GET" && env.request.headers.has_key?("Range")
       next multipart(file, env)
     end
-    if request_headers.includes_word?("Accept-Encoding", "gzip") && config.is_a?(Hash) && config["gzip"] == true && filesize > minsize && Kemal::Utils.zip_types(file_path)
+
+    condition = config.is_a?(Hash) && config["gzip"]? == true && filesize > minsize && Kemal::Utils.zip_types(file_path)
+    if condition && request_headers.includes_word?("Accept-Encoding", "gzip")
       env.response.headers["Content-Encoding"] = "gzip"
       Gzip::Writer.open(env.response) do |deflate|
         IO.copy(file, deflate)
       end
-    elsif request_headers.includes_word?("Accept-Encoding", "deflate") && config.is_a?(Hash) && config["gzip"]? == true && filesize > minsize && Kemal::Utils.zip_types(file_path)
+    elsif condition && request_headers.includes_word?("Accept-Encoding", "deflate")
       env.response.headers["Content-Encoding"] = "deflate"
       Flate::Writer.open(env.response) do |deflate|
         IO.copy(file, deflate)
@@ -148,28 +150,16 @@ end
 private def multipart(file, env : HTTP::Server::Context)
   # See http://httpwg.org/specs/rfc7233.html
   fileb = file.size
+  startb = endb = 0
 
-  range = env.request.headers["Range"]
-  match = range.match(/bytes=(\d{1,})-(\d{0,})/)
-
-  startb = 0
-  endb = 0
-
-  if match
-    if match.size >= 2
-      startb = match[1].to_i { 0 }
-    end
-
-    if match.size >= 3
-      endb = match[2].to_i { 0 }
-    end
+  if match = env.request.headers["Range"].match /bytes=(\d{1,})-(\d{0,})/
+    startb = match[1].to_i { 0 } if match.size >= 2
+    endb = match[2].to_i { 0 } if match.size >= 3
   end
 
-  if endb == 0
-    endb = fileb - 1
-  end
+  endb = fileb - 1 if endb == 0
 
-  if startb < endb && endb < fileb
+  if startb < endb < fileb
     content_length = 1 + endb - startb
     env.response.status_code = 206
     env.response.content_length = content_length
@@ -179,12 +169,12 @@ private def multipart(file, env : HTTP::Server::Context)
     if startb > 1024
       skipped = 0
       # file.skip only accepts values less or equal to 1024 (buffer size, undocumented)
-      until skipped + 1024 > startb
+      until (increase_skipped = skipped + 1024) > startb
         file.skip(1024)
-        skipped += 1024
+        skipped = increase_skipped
       end
-      if skipped - startb > 0
-        file.skip(skipped - startb)
+      if (skipped_minus_startb = skipped - startb) > 0
+        file.skip skipped_minus_startb
       end
     else
       file.skip(startb)
diff --git a/src/kemal/helpers/utils.cr b/src/kemal/helpers/utils.cr
index 30a0d58..cc2bea1 100644
--- a/src/kemal/helpers/utils.cr
+++ b/src/kemal/helpers/utils.cr
@@ -1,9 +1,9 @@
 module Kemal
   module Utils
-    ZIP_TYPES = [".htm", ".html", ".txt", ".css", ".js", ".svg", ".json", ".xml", ".otf", ".ttf", ".woff", ".woff2"]
+    ZIP_TYPES = {".htm", ".html", ".txt", ".css", ".js", ".svg", ".json", ".xml", ".otf", ".ttf", ".woff", ".woff2"}
 
     def self.path_starts_with_slash?(path : String)
-      path.starts_with?("/")
+      path.starts_with? '/'
     end
 
     def self.zip_types(path : String) # https://github.com/h5bp/server-configs-nginx/blob/master/nginx.conf
diff --git a/src/kemal/log_handler.cr b/src/kemal/log_handler.cr
index ede519c..6d04281 100644
--- a/src/kemal/log_handler.cr
+++ b/src/kemal/log_handler.cr
@@ -8,7 +8,7 @@ module Kemal
       time = Time.now
       call_next(context)
       elapsed_text = elapsed_text(Time.now - time)
-      @io << time << " " << context.response.status_code << " " << context.request.method << " " << context.request.resource << " " << elapsed_text << "\n"
+      @io << time << ' ' << context.response.status_code << ' ' << context.request.method << ' ' << context.request.resource << ' ' << elapsed_text << '\n'
       context
     end
 
diff --git a/src/kemal/param_parser.cr b/src/kemal/param_parser.cr
index 66626b4..94e935d 100644
--- a/src/kemal/param_parser.cr
+++ b/src/kemal/param_parser.cr
@@ -21,7 +21,7 @@ module Kemal
     end
 
     private def unescape_url_param(value : String)
-      value.size == 0 ? value : URI.unescape(value)
+      value.empty? ? value : URI.unescape(value)
     rescue
       value
     end
@@ -74,19 +74,11 @@ module Kemal
     end
 
     private def parse_part(part : IO?)
-      if part
-        HTTP::Params.parse(part.gets_to_end)
-      else
-        HTTP::Params.parse("")
-      end
+      HTTP::Params.parse(part ? part.gets_to_end : "")
     end
 
     private def parse_part(part : String?)
-      if part
-        HTTP::Params.parse(part.to_s)
-      else
-        HTTP::Params.parse("")
-      end
+      HTTP::Params.parse part.to_s
     end
   end
 end
diff --git a/src/kemal/route_handler.cr b/src/kemal/route_handler.cr
index b0476c6..528d773 100644
--- a/src/kemal/route_handler.cr
+++ b/src/kemal/route_handler.cr
@@ -56,7 +56,7 @@ module Kemal
     end
 
     private def radix_path(method, path)
-      "/#{method.downcase}#{path}"
+      '/' + method.downcase + path
     end
 
     private def add_to_radix_tree(method, path, route)
diff --git a/src/kemal/static_file_handler.cr b/src/kemal/static_file_handler.cr
index 8fa802e..50d1574 100644
--- a/src/kemal/static_file_handler.cr
+++ b/src/kemal/static_file_handler.cr
@@ -7,7 +7,9 @@ module Kemal
     def call(context : HTTP::Server::Context)
       return call_next(context) if context.request.path.not_nil! == "/"
 
-      unless context.request.method == "GET" || context.request.method == "HEAD"
+      case context.request.method
+      when "GET", "HEAD"
+      else
         if @fallthrough
           call_next(context)
         else
@@ -19,7 +21,6 @@ module Kemal
 
       config = Kemal.config.serve_static
       original_path = context.request.path.not_nil!
-      is_dir_path = original_path.ends_with? "/"
       request_path = URI.unescape(original_path)
 
       # File path cannot contains '\0' (NUL) because all filesystem I know
@@ -30,16 +31,20 @@ module Kemal
       end
 
       expanded_path = File.expand_path(request_path, "/")
-      if is_dir_path && !expanded_path.ends_with? "/"
-        expanded_path = "#{expanded_path}/"
-      end
-      is_dir_path = expanded_path.ends_with? "/"
+      is_dir_path = if original_path.ends_with?('/') && !expanded_path.ends_with? '/'
+                      expanded_path = expanded_path + '/'
+                      true
+                    else
+                      expanded_path.ends_with? '/'
+                    end
 
       file_path = File.join(@public_dir, expanded_path)
       is_dir = Dir.exists? file_path
 
-      if request_path != expanded_path || is_dir && !is_dir_path
-        redirect_to context, "#{expanded_path}#{is_dir && !is_dir_path ? "/" : ""}"
+      if request_path != expanded_path
+        redirect_to context, expanded_path
+      elsif is_dir && !is_dir_path
+        redirect_to context, expanded_path + '/'
       end
 
       if Dir.exists?(file_path)
diff --git a/src/kemal/websocket_handler.cr b/src/kemal/websocket_handler.cr
index d1f3c76..addbecf 100644
--- a/src/kemal/websocket_handler.cr
+++ b/src/kemal/websocket_handler.cr
@@ -17,7 +17,7 @@ module Kemal
     end
 
     def lookup_ws_route(path : String)
-      @routes.find "/ws#{path}"
+      @routes.find "/ws" + path
     end
 
     def add_route(path : String, &handler : HTTP::WebSocket, HTTP::Server::Context -> Void)
@@ -30,12 +30,12 @@ module Kemal
     end
 
     private def radix_path(method, path)
-      "/#{method.downcase}#{path}"
+      '/' + method.downcase + path
     end
 
     private def websocket_upgrade_request?(context)
-      return false unless upgrade = context.request.headers["Upgrade"]?
-      return false unless upgrade.compare("websocket", case_insensitive: true) == 0
+      return unless upgrade = context.request.headers["Upgrade"]?
+      return unless upgrade.compare("websocket", case_insensitive: true) == 0
 
       context.request.headers.includes_word?("Connection", "Upgrade")
     end