Defining new infix operators

Question

It is hard to see what is the question asked here, assuming the latest edit has all the questions.

Should I make it so that instead of infix operators, there are postfix operators, like "String literal"s.contains "Other string literal"s, or do it function style, "String literal"s.contains("Other string literal"s)?

Yes. "String literal"s.contains("Other string literal"s) is the best way - concise, clear to C++ programmers, clear to programmers of other languages (Java and Python strings have methods) and no template magic nor macro magic is used.

How would I improve my code to make it more extensible? As it is right now, it's very polluted. Is there a better/more generalized/less clunky way to do this? For example, to generalize the expressions so that I don't need define statements or to reuse code.

Yep! But only to certain degree (removed the unnecessary consts over there and here):

#define INFIX_OPERATOR(rettype, name, LT, RT) \
struct name\
{\
private:\
    LT* left;\
    RT* right;\
\
protected:\
    LT& lhs() const { return *left; }\
    RT& rhs() const { return *right; }\
\
public: \
    friend name operator+(LT& lhs, name && op)\
    {\
        op.left = &lhs;\
        return op;\
    }\
\
    friend name operator+(name && op, RT& rhs)\
    {\
        op.right = &rhs;\
        return op;\
    }\
\
    name () : left(nullptr), right(nullptr) {}\
\
    operator rettype() const;\
};\
\
inline name :: operator rettype() const

And then you can create your infix operator like this:

#include <iostream>
#include <string>

INFIX_OPERATOR(bool, contains_op, const std::string, const std::string)
{
    return std::string::npos != lhs().find(rhs());
}
#define contains + contains_op() +

int main()
{
    std::string a = "hello";
    std::string b = "hell";
    if(a contains b)
        std::cout << "YES";
}

Note that there is no way to avoid #define contains directive, as there is no way to create macro directive with another macro directive.

What are the practical benefits of this if there are any (ignoring all rationality of using this as real world code. I mean what can you get out of it for what I'm using it for, barring recreational purposes?) Say that my friend, instead of learning C++, wants an easy abstracted interface for his Bash or Perl experience but would like to collaborate without resorting to compiling/linking outside gcc. That way, he can write 'scripts' or 'code' that is C++, and compile and link it with my programs/libraries/interface, whatever.

It seems that you are trying to create a language on top of another language. Prepare for

• Hours and hours trying to test your language.
• Embarrassingly bad diagnostics messages. Try to compile this: std::vector<void> myarr;¹ Then wrap it with macros. And then wrap it in another template. And then in another macros... You get the idea.
• Debugging tools showing processed code.
• Even if your language perfectly integrates with itself, you still have C++ to take care of, with tons of rules and complicated type system. After all, all abstractions are leaky.

If your friend want to program in Perl, just let him do it. These languages are easy to interface with C.

If you're trying to create a language, because the other languages can't cleanly express what you're trying to do, parser generators (Flex/Bison, ANTLR) and LLVM make it easy.

If creating a parser is overkill, take a look at D language mixins. They accept a string created at compile time, and then compile it as if it was inserted directly.

Here...

import std.stdio;
int main()
{
    mixin(`write("Hello world");`); //`contents` is a raw string literal
    return 0;                       //so is r"contents"
}

is equivalent to:

import std.stdio;
int main()
{
    write("Hello world");
    return 0;
}

This is just a simple example. You could have your function that parses a string:

mixin(user1508519s_language(r"(x in a) perform cube"));

¹ - Here is how it looks (gcc 4.7.2):

In file included from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/bits/stl_construct.h:63:0,
                 from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/vector:63,
                 from #templateerrors2.cpp:1:
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/ext/alloc_traits.h
: In instantiation of 'struct __gnu_cxx::__alloc_traits<std::allocator<void> >':

c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
76:28:   required from 'struct std::_Vector_base<void, std::allocator<void> >'
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
208:11:   required from 'class std::vector<void>'
#templateerrors2.cpp:5:19:   required from here
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/ext/alloc_traits.h
:189:53: error: no type named 'reference' in 'class std::allocator<void>'
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/ext/alloc_traits.h
:190:53: error: no type named 'const_reference' in 'class std::allocator<void>'
In file included from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/vector:65:0,
                 from #templateerrors2.cpp:1:
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
 In instantiation of 'class std::vector<void>':
#templateerrors2.cpp:5:19:   required from here
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
292:7: error: forming reference to void
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
467:7: error: forming reference to void
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
684:7: error: invalid parameter type 'std::vector<void>::value_type {aka void}'
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
684:7: error: in declaration 'void std::vector<_Tp, _Alloc>::resize(std::vector<
_Tp, _Alloc>::size_type, std::vector<_Tp, _Alloc>::value_type)'
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
881:7: error: forming reference to void
In file included from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/vector:70:0,
                 from #templateerrors2.cpp:1:
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/vector.tcc:10
8:5: error: forming reference to void
In file included from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/vector:65:0,
                 from #templateerrors2.cpp:1:
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
1003:7: error: forming reference to void
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
1179:7: error: forming reference to void
In file included from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/vector:70:0,
                 from #templateerrors2.cpp:1:
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/vector.tcc:21
6:5: error: forming reference to void
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/vector.tcc:43
9:5: error: forming reference to void
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/vector.tcc:31
6:5: error: forming reference to void
In file included from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/vector:65:0,
                 from #templateerrors2.cpp:1:
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
 In instantiation of 'std::_Vector_base<_Tp, _Alloc>::~_Vector_base() [with _Tp
= void; _Alloc = std::allocator<void>]':
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
247:15:   required from 'std::vector<_Tp, _Alloc>::vector() [with _Tp = void; _A
lloc = std::allocator<void>]'
#templateerrors2.cpp:5:19:   required from here
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
161:9: error: invalid use of 'void'
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
 In instantiation of 'void std::_Vector_base<_Tp, _Alloc>::_M_deallocate(std::_V
ector_base<_Tp, _Alloc>::pointer, std::size_t) [with _Tp = void; _Alloc = std::a
llocator<void>; std::_Vector_base<_Tp, _Alloc>::pointer = void*; std::size_t = u
nsigned int]':
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
161:9:   required from 'std::_Vector_base<_Tp, _Alloc>::~_Vector_base() [with _T
p = void; _Alloc = std::allocator<void>]'
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
247:15:   required from 'std::vector<_Tp, _Alloc>::vector() [with _Tp = void; _A
lloc = std::allocator<void>]'
#templateerrors2.cpp:5:19:   required from here
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
175:4: error: 'struct std::_Vector_base<void, std::allocator<void> >::_Vector_im
pl' has no member named 'deallocate'
In file included from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/bits/stl_algobase.h:66:0,
                 from c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/
c++/vector:61,
                 from #templateerrors2.cpp:1:
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_iterator_
base_types.h: In instantiation of 'struct std::iterator_traits<void*>':
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_construct
.h:127:24:   required from 'void std::_Destroy(_ForwardIterator, _ForwardIterato
r) [with _ForwardIterator = void*]'
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_construct
.h:155:7:   required from 'void std::_Destroy(_ForwardIterator, _ForwardIterator
, std::allocator<_T2>&) [with _ForwardIterator = void*; _Tp = void]'
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_vector.h:
403:9:   required from 'std::vector<_Tp, _Alloc>::~vector() [with _Tp = void; _A
lloc = std::allocator<void>]'
#templateerrors2.cpp:5:19:   required from here
c:\__moje\prog\mingw\bin\../lib/gcc/mingw32/4.7.2/include/c++/bits/stl_iterator_
base_types.h:182:43: error: forming reference to void