diff options
Diffstat (limited to 'src/test/ui/macros/type-macros-hlist.rs')
-rw-r--r-- | src/test/ui/macros/type-macros-hlist.rs | 80 |
1 files changed, 80 insertions, 0 deletions
diff --git a/src/test/ui/macros/type-macros-hlist.rs b/src/test/ui/macros/type-macros-hlist.rs new file mode 100644 index 000000000..946b5bd5d --- /dev/null +++ b/src/test/ui/macros/type-macros-hlist.rs @@ -0,0 +1,80 @@ +// run-pass +#![allow(unused_macro_rules)] + +use std::ops::*; + +#[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)] +struct Nil; + // empty HList +#[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)] +struct Cons<H, T: HList>(H, T); + // cons cell of HList + + // trait to classify valid HLists +trait HList { } +impl HList for Nil { } +impl <H, T: HList> HList for Cons<H, T> { } + +// term-level macro for HLists +macro_rules! hlist({ } => { Nil } ; { $ head : expr } => { + Cons ( $ head , Nil ) } ; { + $ head : expr , $ ( $ tail : expr ) , * } => { + Cons ( $ head , hlist ! ( $ ( $ tail ) , * ) ) } ;); + +// type-level macro for HLists +macro_rules! HList({ } => { Nil } ; { $ head : ty } => { + Cons < $ head , Nil > } ; { + $ head : ty , $ ( $ tail : ty ) , * } => { + Cons < $ head , HList ! ( $ ( $ tail ) , * ) > } ;); + +// nil case for HList append +impl <Ys: HList> Add<Ys> for Nil { + type + Output + = + Ys; + + fn add(self, rhs: Ys) -> Ys { rhs } +} + +// cons case for HList append +impl <Rec: HList + Sized, X, Xs: HList, Ys: HList> Add<Ys> for Cons<X, Xs> + where Xs: Add<Ys, Output = Rec> { + type + Output + = + Cons<X, Rec>; + + fn add(self, rhs: Ys) -> Cons<X, Rec> { Cons(self.0, self.1 + rhs) } +} + +// type macro Expr allows us to expand the + operator appropriately +macro_rules! Expr({ ( $ ( $ LHS : tt ) + ) } => { Expr ! ( $ ( $ LHS ) + ) } ; + { HList ! [ $ ( $ LHS : tt ) * ] + $ ( $ RHS : tt ) + } => { + < Expr ! ( HList ! [ $ ( $ LHS ) * ] ) as Add < Expr ! ( + $ ( $ RHS ) + ) >> :: Output } ; { + $ LHS : tt + $ ( $ RHS : tt ) + } => { + < Expr ! ( $ LHS ) as Add < Expr ! ( $ ( $ RHS ) + ) >> :: + Output } ; { $ LHS : ty } => { $ LHS } ;); + +// test demonstrating term level `xs + ys` and type level `Expr!(Xs + Ys)` +fn main() { + fn aux<Xs: HList, Ys: HList>(xs: Xs, ys: Ys) -> Expr!(Xs + Ys) where + Xs: Add<Ys> { + xs + ys + } + + let xs: HList!(& str , bool , Vec < u64 >) = + hlist!("foo" , false , vec ! [ ]); + let ys: HList!(u64 , [ u8 ; 3 ] , ( )) = + hlist!(0 , [ 0 , 1 , 2 ] , ( )); + + // demonstrate recursive expansion of Expr! + let zs: + Expr!(( + HList ! [ & str ] + HList ! [ bool ] + HList ! [ Vec < u64 > + ] ) + ( HList ! [ u64 ] + HList ! [ [ u8 ; 3 ] , ( ) ] ) + + HList ! [ ]) = aux(xs, ys); + assert_eq!(zs , hlist ! [ + "foo" , false , vec ! [ ] , 0 , [ 0 , 1 , 2 ] , ( ) ]) +} |