diff --git a/src/scanner.jl b/src/scanner.jl
index 084a57e..0e8127a 100644
--- a/src/scanner.jl
+++ b/src/scanner.jl
@@ -352,43 +352,49 @@ end
 # Checkers
 # --------
 
-const whitespace = "\0 \t\r\n\u0085\u2028\u2029"
+yaml_1_1_is_whitespace(c::Char) =
+    c == '\0' || c == ' ' || c == '\t' ||
+    c == '\r' || c == '\n' ||
+    c == '\u85' || c == '\u2028' || c == '\u2029'
 
-
-function check_directive(stream::TokenStream)
+check_directive(stream::TokenStream) =
     stream.column == 0
-end
 
-function check_document_start(stream::TokenStream)
+check_document_start(stream::TokenStream) =
     stream.column == 0 &&
-        prefix(stream.input, 3) == "---" &&
-        in(peek(stream.input, 3), whitespace)
-end
+    prefix(stream.input, 3) == "---" &&
+    yaml_1_1_is_whitespace(peek(stream.input, 3))
 
- function check_document_end(stream::TokenStream)
-     stream.column == 0 &&
-     prefix(stream.input, 3) == "..." &&
-    (in(peek(stream.input, 3), whitespace) || peek(stream.input, 3) === nothing)
- end
+check_document_end(stream::TokenStream) =
+    stream.column == 0 &&
+    prefix(stream.input, 3) == "..." && begin
+        c = peek(stream.input, 3)
+        yaml_1_1_is_whitespace(c) || c === nothing
+    end
 
 function check_block_entry(stream::TokenStream)
-    in(peek(stream.input, 1), whitespace)
+    cnext = peek(stream.input, 1)
+    yaml_1_1_is_whitespace(cnext)
 end
 
-function check_key(stream::TokenStream)
-    stream.flow_level > 0 || in(peek(stream.input, 1), whitespace)
-end
+check_key(stream::TokenStream) =
+    stream.flow_level > 0 || begin
+        cnext = peek(stream.input, 1)
+        yaml_1_1_is_whitespace(cnext)
+    end
 
-function check_value(stream::TokenStream)
-    cnext = peek(stream.input, 1)
-    stream.flow_level > 0 || in(cnext, whitespace) || cnext === nothing
-end
+check_value(stream::TokenStream) =
+    stream.flow_level > 0 || begin
+        cnext = peek(stream.input, 1)
+        yaml_1_1_is_whitespace(cnext) || cnext === nothing
+    end
 
 function check_plain(stream::TokenStream)
-    !in(peek(stream.input), "\0 \t\r\n\u0085\u2028\u2029-?:,[]{}#&*!|>\'\"%@`\uFEFF") ||
-    (!in(peek(stream.input, 1), whitespace) &&
-     (peek(stream.input) == '-' || (stream.flow_level == 0 &&
-                              in(peek(stream.input), "?:"))))
+    c = peek(stream.input)
+    !(yaml_1_1_is_whitespace(c) || c in "-?:,[]{}#&*!|>\'\"%@`\uFEFF") || begin
+        cnext = peek(stream.input, 1)
+        !yaml_1_1_is_whitespace(cnext) && (c == '-' || stream.flow_level == 0 && (c == '?' || c == ':'))
+    end
 end
 
 
@@ -1411,10 +1417,10 @@ function scan_plain(stream::TokenStream)
         while true
             c = peek(stream.input, length)
             cnext = peek(stream.input, length + 1)
-            if in(c, whitespace) ||
+            if yaml_1_1_is_whitespace(c) ||
                 c === nothing ||
                 (stream.flow_level == 0 && c == ':' &&
-                    (cnext === nothing || in(cnext, whitespace))) ||
+                    (cnext === nothing || yaml_1_1_is_whitespace(cnext))) ||
                 (stream.flow_level != 0 && in(c, ",:?[]{}"))
                 break
             end