From b16be42e6dc51e6333372d3d92d10ffd6bb955d2 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Thu, 15 Dec 2016 13:39:51 -0800
Subject: [PATCH] Add `fallback` and simplify `or`

---
 parsimmon/index.d.ts         | 15 +++++++++------
 parsimmon/parsimmon-tests.ts |  5 ++++-
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/parsimmon/index.d.ts b/parsimmon/index.d.ts
index 85ea74cfd9..417cd962b5 100644
--- a/parsimmon/index.d.ts
+++ b/parsimmon/index.d.ts
@@ -83,8 +83,7 @@ declare namespace Parsimmon {
 		/**
 		 * returns a new parser which tries parser, and if it fails uses otherParser.
 		 */
-		or(otherParser: Parser<T>): Parser<T>;
-		or<U>(otherParser: Parser<U>): Parser<any>;
+		or<U>(otherParser: Parser<U>): Parser<T | U>;
 		/**
 		 * returns a new parser which tries parser, and on success calls the given function
 		 * with the result of the parse, which is expected to return another parser, which
@@ -106,14 +105,18 @@ declare namespace Parsimmon {
 		 * transforms the output of parser with the given function.
 		 */
 		map<U>(call: (result: T) => U): Parser<U>;
-		/**
-		 * expects otherParser after parser, but preserves the yield value of parser.
-		 */
-		skip<U>(otherParser: Parser<U>): Parser<T>;
 		/**
 		 * returns a new parser with the same behavior, but which yields aResult.
 		 */
 		result<U>(aResult: U): Parser<U>;
+		/**
+		 * returns a new parser that returns the fallback value if the first parser failed.
+		 */
+		fallback<U>(fallbackValue: U): Parser<T | U>;
+		/**
+		 * expects otherParser after parser, but preserves the yield value of parser.
+		 */
+		skip<U>(otherParser: Parser<U>): Parser<T>;
 		/**
 		 * expects parser zero or more times, and yields an array of the results.
 		 */
diff --git a/parsimmon/parsimmon-tests.ts b/parsimmon/parsimmon-tests.ts
index e0c6e0b00c..6be7eb307a 100644
--- a/parsimmon/parsimmon-tests.ts
+++ b/parsimmon/parsimmon-tests.ts
@@ -38,6 +38,7 @@ var indexPar: Parser<Index>;
 
 var fooPar: Parser<Foo>;
 var barPar: Parser<Bar>;
+var fooOrBarPar: Parser<Foo | Bar>;
 
 // --  --  --  --  --  --  --  --  --  --  --  --  --
 
@@ -84,7 +85,7 @@ fooResult = fooPar.parse(str);
 foo = fooPar.tryParse(str);
 
 fooPar = fooPar.or(fooPar);
-anyPar = fooPar.or(barPar);
+fooOrBarPar = fooPar.or(barPar);
 
 barPar = fooPar.chain((f) => {
 	foo = f;
@@ -108,6 +109,8 @@ fooPar = fooPar.skip(barPar);
 
 barPar = barPar = fooPar.result(bar);
 
+fooOrBarPar = fooPar.fallback(bar);
+
 // --  --  --  --  --  --  --  --  --  --  --  --  --
 
 fooArrPar = fooPar.many();