From bc3464ede77bba781928b7b0f425373a520077a4 Mon Sep 17 00:00:00 2001
From: Flaviu Tamas <tamasflaviu@gmail.com>
Date: Tue, 21 Oct 2014 16:49:29 -0400
Subject: [PATCH 1/2] Modify pegs.nim such that no match will return nil

An empty match will return ""
A zero-length match will return nil

Add test cases

Add news information
---
 lib/pure/pegs.nim | 18 +++++++++++++++++-
 web/news.txt      |  2 ++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/lib/pure/pegs.nim b/lib/pure/pegs.nim
index b2d8a2a4ff..6eb7dee786 100644
--- a/lib/pure/pegs.nim
+++ b/lib/pure/pegs.nim
@@ -737,7 +737,12 @@ proc rawMatch*(s: string, p: Peg, start: int, c: var Captures): int {.
 
 template fillMatches(s, caps, c: expr) =
   for k in 0..c.ml-1:
-    caps[k] = substr(s, c.matches[k][0], c.matches[k][1])
+    let startIdx = c.matches[k][0]
+    let endIdx = c.matches[k][1]
+    if startIdx != -1:
+      caps[k] = substr(s, startIdx, endIdx)
+    else:
+      caps[k] = nil
 
 proc match*(s: string, pattern: Peg, matches: var openArray[string],
             start = 0): bool {.nosideEffect, rtl, extern: "npegs$1Capture".} =
@@ -1767,3 +1772,14 @@ when isMainModule:
 
   assert match("prefix/start", peg"^start$", 7)
 
+  if "foo" =~ peg"{'a'}?.*":
+    assert matches[0] == nil
+  else: assert false
+
+  if "foo" =~ peg"{''}.*":
+    assert matches[0] == ""
+  else: assert false
+
+  if "foo" =~ peg"{'foo'}":
+    assert matches[0] == "foo"
+  else: assert false
diff --git a/web/news.txt b/web/news.txt
index c9374558af..c79eb55cc7 100644
--- a/web/news.txt
+++ b/web/news.txt
@@ -20,6 +20,8 @@ News
   - String case (or any non-ordinal case) statements
     without 'else' are deprecated.
   - Recursive tuple types are not allowed anymore. Use ``object`` instead.
+  - The PEGS module returns ``nil`` instead of ``""`` when an optional capture
+    fails to match
 
   Language Additions
   ------------------

From 218cb7587a351c9a29a7de5961f168a5cdbb5a70 Mon Sep 17 00:00:00 2001
From: Flaviu Tamas <tamasflaviu@gmail.com>
Date: Sun, 26 Oct 2014 09:31:21 -0400
Subject: [PATCH 2/2] re module returns nil on failed captures

- tests included
- news.txt updated
---
 lib/impure/re.nim | 16 +++++++++++++---
 web/news.txt      |  2 ++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/lib/impure/re.nim b/lib/impure/re.nim
index fc9ed3ce06..6e3a69c62c 100644
--- a/lib/impure/re.nim
+++ b/lib/impure/re.nim
@@ -92,7 +92,7 @@ proc matchOrFind(s: string, pattern: Regex, matches: var openArray[string],
     var a = rawMatches[i * 2]
     var b = rawMatches[i * 2 + 1]
     if a >= 0'i32: matches[i-1] = substr(s, int(a), int(b)-1)
-    else: matches[i-1] = ""
+    else: matches[i-1] = nil
   return rawMatches[1] - rawMatches[0]
   
 proc findBounds*(s: string, pattern: Regex, matches: var openArray[string],
@@ -110,7 +110,7 @@ proc findBounds*(s: string, pattern: Regex, matches: var openArray[string],
     var a = rawMatches[i * 2]
     var b = rawMatches[i * 2 + 1]
     if a >= 0'i32: matches[i-1] = substr(s, int(a), int(b)-1)
-    else: matches[i-1] = ""
+    else: matches[i-1] = nil
   return (rawMatches[0].int, rawMatches[1].int - 1)
   
 proc findBounds*(s: string, pattern: Regex, 
@@ -190,7 +190,7 @@ proc find*(s: string, pattern: Regex, matches: var openArray[string],
     var a = rawMatches[i * 2]
     var b = rawMatches[i * 2 + 1]
     if a >= 0'i32: matches[i-1] = substr(s, int(a), int(b)-1)
-    else: matches[i-1] = ""
+    else: matches[i-1] = nil
   return rawMatches[0]
 
 proc find*(s: string, pattern: Regex, start = 0): int =
@@ -310,6 +310,8 @@ proc replacef*(s: string, sub: Regex, by: string): string =
   while true:
     var match = findBounds(s, sub, caps, prev)
     if match.first < 0: break
+    assert result != nil
+    assert s != nil
     add(result, substr(s, prev, match.first-1))
     addf(result, by, caps)
     prev = match.last + 1
@@ -450,6 +452,14 @@ when isMainModule:
     assert matches[1] == "abc"
   else:
     assert false
+  
+  if "abc" =~ re"(cba)?.*":
+    assert matches[0] == nil
+  else: assert false
+
+  if "abc" =~ re"().*":
+    assert matches[0] == ""
+  else: assert false
     
   assert "var1=key; var2=key2".endsWith(re"\w+=\w+")
   assert("var1=key; var2=key2".replacef(re"(\w+)=(\w+)", "$1<-$2$2") ==
diff --git a/web/news.txt b/web/news.txt
index c79eb55cc7..b4316c989c 100644
--- a/web/news.txt
+++ b/web/news.txt
@@ -22,6 +22,8 @@ News
   - Recursive tuple types are not allowed anymore. Use ``object`` instead.
   - The PEGS module returns ``nil`` instead of ``""`` when an optional capture
     fails to match
+  - The re module returns ``nil`` instead of ``""`` when an optional capture
+    fails to match
 
   Language Additions
   ------------------