LEX?? ( Installation Problems )

Hello, we have some problems to install the new verion of PHP4 The following Error occcured creating cache ./config.cache checking for Cygwin environment... no checking for mingw32 environment... no checking host system type... i686-pc-linux-gnu checking for a BSD compatible install... /usr/bin/install -c checking whether build environment is sane... yes checking for gawk... gawk checking whether make sets ${MAKE}... yes checking whether to enable maintainer-specific portions of Makefiles... no Updated php_version.h checking how to run the C preprocessor... cc -E checking for AIX... no 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 for style of include used by make... GNU checking dependency style of gcc... none checking whether gcc and cc understand -c and -o together... yes checking for gcc option to accept ANSI C... none needed checking how to run the C preprocessor... cc -E checking whether compiler supports -R... no checking whether compiler supports -Wl,-rpath,... yes checking for ranlib... ranlib checking whether ln -s works... yes checking for gawk... (cached) 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: lex: command not found >>>configure: error: cannot find output from lex; giving up Wht did go wrong ? Any hints to solve the problem? Thank you Tobi