Implement recover

2 files changed, 27 insertions, 2 deletions

diff --git a/spec/parcom_spec.cr b/spec/parcom_spec.cr
index c395636..d9af3b9 100644
--- a/spec/parcom_spec.cr
+++ b/spec/parcom_spec.cr
@@ -336,7 +336,26 @@ describe Phrase do
   end
 end
 
-pending Recover do
+describe Recover do
+  p = Recover.new(Token.new('t'), '@')
+
+  describe "#parse" do
+    it "succeeds and returns the wrapped parser's value if it succeeds" do
+      tokens = TokenStream.from_string("testing")
+      result = p.parse(tokens)
+
+      result.tokens.should eq(tokens[1..])
+      result.value.should eq('t')
+    end
+
+    it "succeeds and returns the default value without modifying the input of the wrapped parser fails" do
+      tokens = TokenStream.from_string("_____")
+      result = p.parse(tokens)
+
+      result.tokens.should eq(tokens)
+      result.value.should eq('@')
+    end
+  end
 end
 
 pending Optional do
diff --git a/src/parcom.cr b/src/parcom.cr
index 4d49a97..f102728 100644
--- a/src/parcom.cr
+++ b/src/parcom.cr
@@ -192,7 +192,13 @@ module Parcom
     end
   end
 
-  class Recover
+  class Recover(T, V) < Parser(T, V)
+    def initialize(@p : Parser(T, V), @default : V)
+    end
+
+    def parse(tokens : TokenStream(T)) : Result(T, V)
+      @p.parse?(tokens) || Result.new(tokens, @default)
+    end
   end
 
   class Optional