Implement custom error messages for Parser.flunk

1 files changed, 8 insertions, 1 deletions

diff --git a/src/parcom/parser.cr b/src/parcom/parser.cr
index e7442db..2b058d4 100644
--- a/src/parcom/parser.cr
+++ b/src/parcom/parser.cr
@@ -36,9 +36,16 @@ module Parcom
       Parser(T, U).new("Pure #{value}") { |tokens| Result.new(tokens, value) }
     end
 
+    # Creates a parser that always fails with the given error message.
+    def self.flunk(message : String) : Parser(T, U)
+      Parser(T, U).new("Flunk") do |_|
+        raise ParserFail.new(message)
+      end
+    end
+
     # Creates a parser that always fails.
     def self.flunk : Parser(T, U)
-      Parser(T, U).new("Flunk") { |_| raise ParserFail.new("Flunked parser") }
+      flunk("Flunked parser")
     end
 
     # Creates a parser that returns the first token in the input stream.