unable to `brew install haproxy`. `brew doctor` says `Your system is raring to brew.`

brew install haproxy

==> Downloading http://haproxy.1wt.eu/download/1.4/src/haproxy-1.4.17.tar.gz
File already downloaded in /Users/tom/Library/Caches/Homebrew
/usr/bin/tar xf /Users/tom/Library/Caches/Homebrew/haproxy-1.4.17.tar.gz
==> make TARGET=generic USE_KQUEUE=1 USE_POLL=1 USE_PCRE=1 PREFIX=/usr/local/Cellar/haproxy/1.4.17 DOCDIR=/usr/local/Cellar/haproxy/1.4.17/share/doc/haproxy CC=/usr/bin/clang CFLAGS=-Os -w -pipe -march=native -Qunused-arguments LDFLAGS= install
make TARGET=generic USE_KQUEUE=1 USE_POLL=1 USE_PCRE=1 PREFIX=/usr/local/Cellar/haproxy/1.4.17 DOCDIR=/usr/local/Cellar/haproxy/1.4.17/share/doc/haproxy CC=/usr/bin/clang CFLAGS=-Os -w -pipe -march=native -Qunused-arguments LDFLAGS= install
/usr/bin/clang -Iinclude -Iebtree -Wall -Os -w -pipe -march=native -Qunused-arguments       -DTPROXY -DENABLE_POLL -DENABLE_KQUEUE -DUSE_PCRE -I/usr/local/include  -DCONFIG_HAPROXY_VERSION=\"1.4.17\" -DCONFIG_HAPROXY_DATE=\"2011/09/05\" \
	      -DBUILD_TARGET='"generic"' \
	      -DBUILD_ARCH='""' \
	      -DBUILD_CPU='"generic"' \
	      -DBUILD_CC='"/usr/bin/clang"' \
	      -DBUILD_CFLAGS='"-Os -w -pipe -march=native -Qunused-arguments"' \
	      -DBUILD_OPTIONS='"USE_POLL=1 USE_KQUEUE=1 USE_PCRE=1"' \
	       -c -o src/haproxy.o src/haproxy.c
/usr/bin/clang -Iinclude -Iebtree -Wall -Os -w -pipe -march=native -Qunused-arguments       -DTPROXY -DENABLE_POLL -DENABLE_KQUEUE -DUSE_PCRE -I/usr/local/include  -DCONFIG_HAPROXY_VERSION=\"1.4.17\" -DCONFIG_HAPROXY_DATE=\"2011/09/05\" -c -o src/sessionhash.o src/sessionhash.c
/usr/bin/clang -Iinclude -Iebtree -Wall -Os -w -pipe -march=native -Qunused-arguments       -DTPROXY -DENABLE_POLL -DENABLE_KQUEUE -DUSE_PCRE -I/usr/local/include  -DCONFIG_HAPROXY_VERSION=\"1.4.17\" -DCONFIG_HAPROXY_DATE=\"2011/09/05\" -c -o src/base64.o src/base64.c
/usr/bin/clang -Iinclude -Iebtree -Wall -Os -w -pipe -march=native -Qunused-arguments       -DTPROXY -DENABLE_POLL -DENABLE_KQUEUE -DUSE_PCRE -I/usr/local/include  -DCONFIG_HAPROXY_VERSION=\"1.4.17\" -DCONFIG_HAPROXY_DATE=\"2011/09/05\" -c -o src/protocols.o src/protocols.c
In file included from src/haproxy.c:54:
In file included from include/common/cfgparse.h:29:
In file included from include/types/proxy.h:33:
include/common/regex.h:28:10: fatal error: 'pcre.h' file not found
#include <pcre.h>
         ^
/usr/bin/clang -Iinclude -Iebtree -Wall -Os -w -pipe -march=native -Qunused-arguments       -DTPROXY -DENABLE_POLL -DENABLE_KQUEUE -DUSE_PCRE -I/usr/local/include  -DCONFIG_HAPROXY_VERSION=\"1.4.17\" -DCONFIG_HAPROXY_DATE=\"2011/09/05\" -c -o src/uri_auth.o src/uri_auth.c
/usr/bin/clang -Iinclude -Iebtree -Wall -Os -w -pipe -march=native -Qunused-arguments       -DTPROXY -DENABLE_POLL -DENABLE_KQUEUE -DUSE_PCRE -I/usr/local/include  -DCONFIG_HAPROXY_VERSION=\"1.4.17\" -DCONFIG_HAPROXY_DATE=\"2011/09/05\" -c -o src/standard.o src/standard.c
/usr/bin/clang -Iinclude -Iebtree -Wall -Os -w -pipe -march=native -Qunused-arguments       -DTPROXY -DENABLE_POLL -DENABLE_KQUEUE -DUSE_PCRE -I/usr/local/include  -DCONFIG_HAPROXY_VERSION=\"1.4.17\" -DCONFIG_HAPROXY_DATE=\"2011/09/05\" -c -o src/buffers.o src/buffers.c
1 error generated.
make: *** [src/haproxy.o] Error 1
make: *** Waiting for unfinished jobs....
In file included from src/uri_auth.c:20:
In file included from include/proto/log.h:32:
In file included from include/types/proxy.h:33:
include/common/regex.h:28:10: fatal error: 'pcre.h' file not found
#include <pcre.h>
         ^
1 error generated.
make: *** [src/uri_auth.o] Error 1
In file included from src/standard.c:25:
In file included from include/proto/log.h:32:
In file included from include/types/proxy.h:33:
include/common/regex.h:28:10: fatal error: 'pcre.h' file not found
#include <pcre.h>
         ^
1 error generated.
make: *** [src/standard.o] Error 1
In file included from src/buffers.c:20:
In file included from include/proto/buffers.h:35:
In file included from include/types/global.h:30:
In file included from include/types/proxy.h:33:
include/common/regex.h:28:10: fatal error: 'pcre.h' file not found
#include <pcre.h>
         ^
1 error generated.
make: *** [src/buffers.o] Error 1
==> Exit Status: 2
http://github.com/mxcl/homebrew/blob/master/Library/Formula/haproxy.rb#L10
==> Environment
HOMEBREW_VERSION: 0.8.1
HEAD: 0e8ea8aae9dadda53d0dc0cf680d383981770be9
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CELLAR: /usr/local/Cellar
Hardware: quad-core 64-bit sandybridge
OS X: 10.7.3
Kernel Architecture: x86_64
Xcode: 4.3
GCC-4.0: N/A
GCC-4.2: build 5666
LLVM: build 2335
Clang: 2.1 build 163
MacPorts or Fink? false
X11: /usr/X11
System Ruby: 1.8.7-249
/usr/bin/ruby => /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
Which Perl:   /usr/bin/perl
Which Python: /usr/bin/python
Which Ruby:   /usr/bin/ruby => /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
==> Build Flags
CC: /usr/bin/clang
CXX: /usr/bin/clang++ => /usr/bin/clang
LD: /usr/bin/clang
CFLAGS: -Os -w -pipe -march=native -Qunused-arguments
CXXFLAGS: -Os -w -pipe -march=native -Qunused-arguments
MAKEFLAGS: -j4

Error: Failed executing: make TARGET=generic USE_KQUEUE=1 USE_POLL=1 USE_PCRE=1 PREFIX=/usr/local/Cellar/haproxy/1.4.17 DOCDIR=/usr/local/Cellar/haproxy/1.4.17/share/doc/haproxy CC=/usr/bin/clang CFLAGS=-Os\ -w\ -pipe\ -march=native\ -Qunused-arguments LDFLAGS= install
If `brew doctor' does not help diagnose the issue, please report the bug:
    https://github.com/mxcl/homebrew/wiki/checklist-before-filing-a-new-issue