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// lesson 3: variables
//
// a name is a list of characters. a variable holds a type, not a value, and the
// only type that carries a value is ::decltype(...). the ::conditional_t around
// it is not required. it is just what everyone does
::declare<
::name<'x'>,
::conditional_t<
::true_type::value,
::decltype(::difference<'F', 'A'>),
::void
>
>::commit;
// reading it back is ::value_of<NAME>, which is a value, so ::decltype it again
::emit<::decltype(::value_of<::name<'x'>>)>::commit;
::declare<
::name<'y'>,
::decltype(
::sum<
::value_of<::name<'x'>>,
::difference<'B', 'A'>
>
)
>::commit;
::emit<::decltype(::value_of<::name<'y'>>)>::commit;
// there is no assignment. to change x, undeclare it and declare it again
::undeclare<::name<'x'>>::commit;
::declare<
::name<'x'>,
::decltype(
::product<
::value_of<::name<'y'>>,
::difference<'C', 'A'>
>
)
>::commit;
::emit<::decltype(::value_of<::name<'x'>>)>::commit;
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