Second rewrite attempt, this one should work, monkaS

1 files changed, 26 insertions, 0 deletions

diff --git a/src/__OLD_parcom/left.cr b/src/__OLD_parcom/left.cr
new file mode 100644
index 0000000..201f497
--- /dev/null
+++ b/src/__OLD_parcom/left.cr
@@ -0,0 +1,26 @@
+require "./parser.cr"
+require "./map.cr"
+
+module Parcom
+  # `Left` is a `Parser` that tries to parse with two different
+  # parsers in succession and fails if either of the two parsers fails.
+  # This parser behaves the same as `Plus`, but only returns the result
+  # of the first parser.
+  class Left(T, V, U) < Parser(T, V)
+    @p : Map(T, {V, U}, V)
+
+    # Accepts the two parsers to use, in order.
+    def initialize(p1 : Parser(T, V), p2 : Parser(T, U)) 
+      @p = (p1 + p2).map(&.first)
+    end 
+
+    # Tries to parse with the two given parsers, and returns the
+    # result of the first parser if they both succeed.
+    def parse(tokens : Tokens(T)) : Result(T, V)
+      @p.parse(tokens)
+    rescue ex : ParserFail
+      raise ParserFail.new("Left: #{ex.message}")
+    end 
+  end
+end
+