//! This macro implements a syntax that emulates Pythons
//! [`generator-expression`] syntax in a form more compatible with rusts
//! usual syntax.
//!
//! This means that there a few small differences between the python syntax
//! and the syntax prvided in this macro:
//!
//! * The expression in the beginning of the generator expression
//! must end with a semicolon (;).
//! * The pattern between the `for` and `in` tokens is a fully-fledged
//! rust pattern, which can be as simple as a simple token and as complex
//! as struct destructuring.
//! * The expression defining the iterator after the `for` token
//! (and potentially before an `if` token) must evaluate to either an
//! `Iterator` or an `impl IntoIterator`, and end with a semicolon (;).
//! * The conditional expression after the `if` expression expression
//! (and potentially before a `for` token) must evaluate to a boolean,
//! and end with a semicolon (;).
//!
//! The expression replaced by the `comp!()` macro invocation is a lazy
//! iterator whose lifetime is bound by any references it needs to capture.
//! This means that it can be `.collect()`ed into any container you like.
//!
//! # Examples
//!
//! Simple generator expression with a conditional:
//! ```
//! use py_comp::comp;
//!
//! #[derive(Debug, PartialEq, Eq)]
//! struct Foo(i32);
//!
//! let arr = &[Foo(11), Foo(12)];
//!
//! // Notice the semicolons
//! let comp_vector = comp!(item; for item in arr; if item.0 % 10 == 2;)
//! .collect::<Vec<&Foo>>();
//!
//! assert_eq!(comp_vector, vec![&Foo(12)])
//! ```
//!
//! Triple cartesian product with conditions and patterns:
//! ```
//! use py_comp::comp;
//!
//! #[derive(Debug, PartialEq, Eq)]
//! struct Foo(i32);
//!
//! // These need to be references to arrays because of how the closures
//! // that the macro expands to capture their environment.
//! let x = &[(Foo(11), "foo"), (Foo(12), "bar")];
//! let y = &[Foo(21), Foo(22)];
//! let z = &[Foo(31), Foo(32)];
//!
//! let xyz = comp!(
//! (a, b, c);
//! for (a, _text) in x; // You can use any function parameter pattern.
//! if a.0 % 10 == 2;
//! for b in y; // Obviously not every level requires a conditional.
//! for c in z;
//! if c.0 % 10 == 2;
//! )
//! .collect::<Vec<(&Foo, &Foo, &Foo)>>();
//!
//! // The result vector here is short for illustration purposes
//! // but can be as long as long as you need it to be.
//! assert_eq!(xyz, vec![(&Foo(12), &Foo(21), &Foo(32)), (&Foo(12), &Foo(22), &Foo(32))])
//! ```
//!
//! [`generator-expression`]: https://docs.python.org/3/reference/expressions.html#generator-expressions
//!
// Check that the type of the expression passed here implements IntoIterator.
// Hopefully this optimizes away in release builds.
/// A Python-like lazy generator-expression
///
/// For details see [module level documentation][super]
///
/// [super]: ../py_comp/index.html