# FindFLEX

Find flex executable and provides a macro to generate custom build rules

The module defines the following variables:

    FLEX_FOUND - true is flex executable is found
    FLEX_EXECUTABLE - the path to the flex executable
    FLEX_VERSION - the version of flex
    FLEX_LIBRARIES - The flex libraries
    FLEX_INCLUDE_DIRS - The path to the flex headers

The minimum required version of flex can be specified using the standard syntax, e.g. find_package(FLEX 2.5.13)

If flex is found on the system, the module provides the macro:

    FLEX_TARGET(Name FlexInput FlexOutput [COMPILE_FLAGS <string>])

which creates a custom command to generate the <FlexOutput> file from the <FlexInput> file. If COMPILE_FLAGS option is specified, the next parameter is added to the flex command line. Name is an alias used to get details of this custom command. Indeed the macro defines the following variables:

    FLEX_${Name}_DEFINED - true is the macro ran successfully
    FLEX_${Name}_OUTPUTS - the source file generated by the custom rule, an
    alias for FlexOutput
    FLEX_${Name}_INPUT - the flex source file, an alias for ${FlexInput}

Flex scanners oftenly use tokens defined by Bison: the code generated by Flex depends of the header generated by Bison. This module also defines a macro:

    ADD_FLEX_BISON_DEPENDENCY(FlexTarget BisonTarget)

which adds the required dependency between a scanner and a parser where <FlexTarget> and <BisonTarget> are the first parameters of respectively FLEX_TARGET and BISON_TARGET macros.

    ====================================================================
    Example:

    find_package(BISON)
    find_package(FLEX)

    BISON_TARGET(MyParser parser.y ${CMAKE_CURRENT_BINARY_DIR}/parser.cpp)
    FLEX_TARGET(MyScanner lexer.l  ${CMAKE_CURRENT_BINARY_DIR}/lexer.cpp)
    ADD_FLEX_BISON_DEPENDENCY(MyScanner MyParser)

     include_directories(${CMAKE_CURRENT_BINARY_DIR})
     add_executable(Foo
        Foo.cc
        ${BISON_MyParser_OUTPUTS}
        ${FLEX_MyScanner_OUTPUTS}
     )
    ====================================================================