Problem when ruuning ./configure

I have installed Apache1.3.29 on my linux pc, and when I try to install php4.3.4, I got the following error when try to run ./configure , how do I fix it? Regards, Lillian [root@itcl php-4.3.4]# ./configure loading cache ./config.cache checking host system type... i686-pc-linux-gnu checking for gcc... gcc checking whether the C compiler (gcc ) works... yes checking whether the C compiler (gcc ) is a cross-compiler... no checking whether we are using GNU C... yes checking whether gcc accepts -g... yes checking whether gcc and cc understand -c and -o together... yes checking how to run the C preprocessor... gcc -E checking for AIX... no checking if compiler supports -R... no checking if compiler supports -Wl,-rpath,... yes checking for re2c... exit 0; checking for ranlib... ranlib checking whether ln -s works... yes checking for gawk... gawk checking for bison... no checking for byacc... no configure: warning: You will need bison if you want to regenerate the PHP parsers. checking for flex... lex checking for yywrap in -ll... no checking lex output file root... ./configure: line 2425: lex: command not found configure: error: cannot find output from lex; giving up