If you #define END as "return(0);}" and put "int main(){" at the bottom of basic.hpp, you can have a complete BASIC program with #include "basic.hpp" at the top as the only indication that it's C++.
#include "basic.hpp"
_10: LET X = 1;
// ...
_150: END
I think multiple data types could also be added in a way that mostly fits with BASIC syntax. GW-BASIC uses sigil suffixes on variable names to denote their type:[1]
Something like this might be possible with unions (e.g. _10: LET X.D = 3.14; _20: LET N.I = 42;), or you can tolerate a few different LET macros (LETS, LETI, LETD).
But the macros were the least of its problems: It allocated memory by trapping SIGSEGV (SIGnal for SEGmentiation Violation; that is, the signal the OS sends a program when it's tried to access memory beyond the region it owns); the function which caught SIGSEGV allocated more RAM. This made it difficult to port sh to the Motorola 68000-based computers which were the first generation of Unix workstations.
] 10 PRINT "HELLO'
] RUN
ERROR
In file included from dummy.cpp:1:
In file included from /usr/include/c++/v1/vector:243:
In file included from /usr/include/c++/v1/__bit_reference:15:
In file included from /usr/include/c++/v1/algorithm:594:
/usr/include/c++/v1/memory:1425:36: error: calling a private constructor of class 'std::__1::unique_ptr<int,
std::__1::default_delete<int> >'
::new ((void*)__p) _Tp(_STD::forward<_Args>(__args)...);
^
/usr/include/c++/v1/memory:1358:14: note: in instantiation of function template specialization
'std::__1::allocator_traits<std::__1::allocator<std::__1::unique_ptr<int, std::__1::default_delete<int> > >
>::__construct<std::__1::unique_ptr<int, std::__1::default_delete<int> >, std::__1::unique_ptr<int,
std::__1::default_delete<int> > &>' requested here
{__construct(__has_construct<allocator_type, pointer, _Args...>(),
^
/usr/include/c++/v1/vector:781:25: note: in instantiation of function template specialization
'std::__1::allocator_traits<std::__1::allocator<std::__1::unique_ptr<int, std::__1::default_delete<int> > >
>::construct<std::__1::unique_ptr<int, std::__1::default_delete<int> >, std::__1::unique_ptr<int,
std::__1::default_delete<int> > &>' requested here
__alloc_traits::construct(__a, _STD::__to_raw_pointer(this->__end_), *__first);
^
/usr/include/c++/v1/vector:924:9: note: in instantiation of function template specialization
'std::__1::vector<std::__1::unique_ptr<int, std::__1::default_delete<int> >,
std::__1::allocator<std::__1::unique_ptr<int, std::__1::default_delete<int> > >
>::__construct_at_end<std::__1::unique_ptr<int, std::__1::default_delete<int> > *>' requested here
__construct_at_end(__x.__begin_, __x.__end_);
^
dummy.cpp:7:37: note: in instantiation of member function 'std::__1::vector<std::__1::unique_ptr<int,
std::__1::default_delete<int> >, std::__1::allocator<std::__1::unique_ptr<int, std::__1::default_delete<int> > >
>::vector' requested here
std::vector<unique_ptr<int>> bar = foo;
^
/usr/include/c++/v1/memory:1997:5: note: declared private here
unique_ptr(const unique_ptr&);
^
1 error generated.
That's wonderful/abusive. There used to be a macro assembler for the Apple ][ that came with an add-on package of macros that provided a BASIC-like language. It was heavily advertised in Nibble Magazine.
It seems someone managed to dig it up, collect some recollections by the author and demo it a few years ago:
If you'd like to fool around with an Applesoft BASIC compatible interpreter that comes with almost 1000 listings, check out DiscoRunner http://discorunner.com
I did something similar in C but I called it HereC. I mostly just did #define begin { and #define end } the other thing I did was make && to AND and || to OR was fun for a few minutes, then I never went back to it.
[1] http://www.antonis.de/qbebooks/gwbasman/chapter%206.html