brew install spidermonkey

spidermonkey.log

checking for tm_zone tm_gmtoff in struct tm... yes
checking for readline in -lreadline... no
configure: error: No system readline library found.
Exit status: 1

http://github.com/mxcl/homebrew/blob/master/Library/Formula/spidermonkey.rb#L55

==> Environment
HOMEBREW_VERSION: 0.7.1
HEAD: 857678439f00f7c2311275ca4a0e8d0fd119c236
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CELLAR: /usr/local/Cellar
HOMEBREW_REPOSITORY: /usr/local
HOMEBREW_LIBRARY_PATH: /usr/local/Library/Homebrew
Hardware: dual-core 64-bit core2
OS X: 10.7
Kernel Architecture: i386
Ruby: 1.8.7-249
/usr/bin/ruby => /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
Xcode: 4.1
GCC-4.0: N/A 
GCC-4.2: build 5666 
LLVM: build 2335 
MacPorts or Fink? false
X11 installed? true

==> Build Flags
CC: /usr/bin/cc => /Developer/usr/llvm-gcc-4.2/bin/llvm-gcc-4.2
CXX: /usr/bin/c++ => /Developer/usr/llvm-gcc-4.2/bin/llvm-g++-4.2
LD: /usr/bin/cc => /Developer/usr/llvm-gcc-4.2/bin/llvm-gcc-4.2
CFLAGS: -O3 -march=core2 -w -pipe
CXXFLAGS: -O3 -march=core2 -w -pipe
CPPFLAGS: -I/usr/local/Cellar/readline/6.1/include
LDFLAGS: -L/usr/local/Cellar/readline/6.1/lib
MAKEFLAGS: -j2
PKG_CONFIG_PATH: /usr/local/Cellar/readline/6.1/lib/pkgconfig
Error: Failure while executing: ../js/src/configure --prefix=/usr/local/Cellar/spidermonkey/1.8.5 --enable-readline --enable-threadsafe --with-system-nspr
Please follow the instructions to report this bug at: 
https://github.com/mxcl/homebrew/wiki/new-issue

Also try:
  `brew doctor` to check your setup for common problems.
  `brew missing` to check installed packages for missing deps.
biow0lf$