Implement FirstOf

1 files changed, 25 insertions, 1 deletions

diff --git a/src/parcom.cr b/src/parcom.cr
index cb3408a..2a61c2d 100644
--- a/src/parcom.cr
+++ b/src/parcom.cr
@@ -405,7 +405,31 @@ module Parcom
   class StopIf
   end
 
-  class FirstOf
+  class FirstOf(T, V) < Parser(T, V)
+    @p : Parser(T, V)
+
+    def initialize(ps : Iterable(Parser(T, V)))
+      ps_iter = ps.each
+      p = ps_iter.next
+
+      if p.is_a?(Iterator::Stop)
+        raise ArgumentError.new("FirstOf requires atleast one parser, got none")
+      end
+
+      @p = p
+      p = ps_iter.next
+
+      until p.is_a?(Iterator::Stop)
+        @p = @p | p
+        p = ps_iter.next
+      end
+    end
+
+    def parse(tokens : TokenStream(T)) : Result(T, V)
+      @p.parse(tokens)
+    rescue ex : ParserException
+      raise ParserException.new("FirstOf: #{ex.message}")
+    end
   end
 
   class SepBy