1 files changed, 19 insertions, 2 deletions
diff --git a/src/parcom.cr b/src/parcom.cr
index 14d2e44..760a450 100644
--- a/src/parcom.cr
+++ b/src/parcom.cr
@@ -133,7 +133,7 @@ module Parcom
       result = @p.parse(tokens)
 
       unless @f.call(result.value)
-        raise ParserException.new("Assert: predicate failed")
+        raise ParserException.new("Assert: predicate failed for <#{result.value}>")
       end
 
       result
@@ -153,6 +153,8 @@ module Parcom
 
     def parse(tokens : TokenStream(T)) : Result(T, T)
       @p.parse(tokens)
+    rescue ex : ParserException
+      raise ParserException.new("Token <#{@expected}>: #{ex.message}")
     end
   end
 
@@ -226,7 +228,22 @@ module Parcom
     end
   end
 
-  class Tokens
+  class Tokens(T) < Parser(T, Array(T))
+    def initialize(@expected : Iterable(T))
+    end
+
+    # TODO: this can probably be optimised more for Arrays
+    # TODO: might be better to use #zip?
+    def parse(tokens : TokenStream(T)) : Result(T, Array(T))
+      parsed_tokens = [] of T
+
+      @expected.each_with_index do |t, i|
+        r = Token.new(t).parse(tokens[i..])
+        parsed_tokens << r.value
+      end
+
+      Result.new(tokens[parsed_tokens.size..], parsed_tokens)
+    end
   end
 
   class Many