Second rewrite attempt, this one should work, monkaS

1 files changed, 28 insertions, 0 deletions

diff --git a/src/__OLD_parcom/alt.cr b/src/__OLD_parcom/alt.cr
new file mode 100644
index 0000000..dedd41d
--- /dev/null
+++ b/src/__OLD_parcom/alt.cr
@@ -0,0 +1,28 @@
+require "./parser.cr"
+
+module Parcom
+  # `Alt` is a `Parser` that accepts two other parsers and tries
+  # to parse with one of them.
+  # If the first (left) parser succeeds, its result is returned.
+  # If the first parser fails, it will try the second (right) parser.
+  class Alt(T, V) < Parser(T, V)
+    # Accepts the two parsers to try to parse with.
+    def initialize(@p1 : Parser(T, V), @p2 : Parser(T, V))
+    end
+
+    # Tries to parse using both parsers.
+    #
+    # It will initially try to parse with the first parser.
+    # If it fails, it will try to parse with the second parser.
+    def parse(tokens : Tokens(T)) : Result(T, V)
+      @p1.parse(tokens)
+    rescue ex1 : ParserFail
+      begin
+        @p2.parse(tokens)
+      rescue ex2 : ParserFail
+        raise ParserFail.new("Alt (#{ex1.message}), (#{ex2.message})")
+      end
+    end
+  end
+end
+