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    use super::*;

    #[derive(Debug, Clone, Eq, PartialEq, Hash)]
    pub enum ConstExpr {
        /// A function call
        ///
        /// The first field resolves to the function itself,
        /// and the second field is the list of arguments
        Call(Box<ConstExpr>, Vec<ConstExpr>),

        /// A binary operation (For example: `a + b`, `a * b`)
        Binary(BinOp, Box<ConstExpr>, Box<ConstExpr>),

        /// A unary operation (For example: `!x`, `*x`)
        Unary(UnOp, Box<ConstExpr>),

        /// A literal (For example: `1`, `"foo"`)
        Lit(Lit),

        /// A cast (`foo as f64`)
        Cast(Box<ConstExpr>, Box<Ty>),

        /// Variable reference, possibly containing `::` and/or type
        /// parameters, e.g. foo::bar::<baz>.
        Path(Path),

        /// An indexing operation (`foo[2]`)
        Index(Box<ConstExpr>, Box<ConstExpr>),

        /// No-op: used solely so we can pretty-print faithfully
        Paren(Box<ConstExpr>),

        /// If compiling with full support for expression syntax, any expression is
        /// allowed
        Other(Other),
    }

    #[cfg(not(feature = "full"))]
    #[derive(Debug, Clone, Eq, PartialEq, Hash)]
    pub struct Other {
        _private: (),
    }

    #[cfg(feature = "full")]
    pub type Other = Expr;

    #[cfg(feature = "parsing")]
    pub mod parsing {
        use super::*;
        use {BinOp, Ty};
        use lit::parsing::lit;
        use op::parsing::{binop, unop};
        use ty::parsing::{path, ty};

        named!(pub const_expr -> ConstExpr, do_parse!(
            mut e: alt!(
                expr_unary
                |
                expr_lit
                |
                expr_path
                |
                expr_paren
                // Cannot handle ConstExpr::Other here because for example
                // `[u32; n!()]` would end up successfully parsing `n` as
                // ConstExpr::Path and then fail to parse `!()`. Instead, callers
                // are required to handle Other. See ty::parsing::array_len and
                // data::parsing::discriminant.
            ) >>
            many0!(alt!(
                tap!(args: and_call => {
                    e = ConstExpr::Call(Box::new(e), args);
                })
                |
                tap!(more: and_binary => {
                    let (op, other) = more;
                    e = ConstExpr::Binary(op, Box::new(e), Box::new(other));
                })
                |
                tap!(ty: and_cast => {
                    e = ConstExpr::Cast(Box::new(e), Box::new(ty));
                })
                |
                tap!(i: and_index => {
                    e = ConstExpr::Index(Box::new(e), Box::new(i));
                })
            )) >>
            (e)
        ));

        named!(and_call -> Vec<ConstExpr>, do_parse!(
            punct!("(") >>
            args: terminated_list!(punct!(","), const_expr) >>
            punct!(")") >>
            (args)
        ));

        named!(and_binary -> (BinOp, ConstExpr), tuple!(binop, const_expr));

        named!(expr_unary -> ConstExpr, do_parse!(
            operator: unop >>
            operand: const_expr >>
            (ConstExpr::Unary(operator, Box::new(operand)))
        ));

        named!(expr_lit -> ConstExpr, map!(lit, ConstExpr::Lit));

        named!(expr_path -> ConstExpr, map!(path, ConstExpr::Path));

        named!(and_index -> ConstExpr, delimited!(punct!("["), const_expr, punct!("]")));

        named!(expr_paren -> ConstExpr, do_parse!(
            punct!("(") >>
            e: const_expr >>
            punct!(")") >>
            (ConstExpr::Paren(Box::new(e)))
        ));

        named!(and_cast -> Ty, do_parse!(
            keyword!("as") >>
            ty: ty >>
            (ty)
        ));
    }

    #[cfg(feature = "printing")]
    mod printing {
        use super::*;
        use quote::{Tokens, ToTokens};

        impl ToTokens for ConstExpr {
            fn to_tokens(&self, tokens: &mut Tokens) {
                match *self {
                    ConstExpr::Call(ref func, ref args) => {
                        func.to_tokens(tokens);
                        tokens.append("(");
                        tokens.append_separated(args, ",");
                        tokens.append(")");
                    }
                    ConstExpr::Binary(op, ref left, ref right) => {
                        left.to_tokens(tokens);
                        op.to_tokens(tokens);
                        right.to_tokens(tokens);
                    }
                    ConstExpr::Unary(op, ref expr) => {
                        op.to_tokens(tokens);
                        expr.to_tokens(tokens);
                    }
                    ConstExpr::Lit(ref lit) => lit.to_tokens(tokens),
                    ConstExpr::Cast(ref expr, ref ty) => {
                        expr.to_tokens(tokens);
                        tokens.append("as");
                        ty.to_tokens(tokens);
                    }
                    ConstExpr::Path(ref path) => path.to_tokens(tokens),
                    ConstExpr::Index(ref expr, ref index) => {
                        expr.to_tokens(tokens);
                        tokens.append("[");
                        index.to_tokens(tokens);
                        tokens.append("]");
                    }
                    ConstExpr::Paren(ref expr) => {
                        tokens.append("(");
                        expr.to_tokens(tokens);
                        tokens.append(")");
                    }
                    ConstExpr::Other(ref other) => {
                        other.to_tokens(tokens);
                    }
                }
            }
        }

        #[cfg(not(feature = "full"))]
        impl ToTokens for Other {
            fn to_tokens(&self, _tokens: &mut Tokens) {
                unreachable!()
            }
        }
    }

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