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|
extern crate proc_macro;
use dhall_core::context::Context;
use dhall_core::*;
use proc_macro2::Literal;
use proc_macro2::TokenStream;
use quote::quote;
#[proc_macro]
pub fn dhall_expr(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input_str = input.to_string();
let expr: Box<Expr<_, X, Import>> = parser::parse_expr(&input_str).unwrap();
let no_import =
|_: &Import| -> X { panic!("Don't use import in dhall!()") };
let expr = expr.take_ownership_of_labels().map_embed(&no_import);
let output = dhall_to_tokenstream::<String>(&expr, &Context::new());
output.into()
}
// Returns an expression of type Expr<_, _>. Expects input variables
// to be of type Box<Expr<_, _>> (future-proof for structural sharing).
fn dhall_to_tokenstream<L: StringLike>(
expr: &Expr<L, X, X>,
ctx: &Context<L, ()>,
) -> TokenStream {
use dhall_core::Expr::*;
match expr {
e @ Var(_) => {
let v = dhall_to_tokenstream_bx(e, ctx);
quote! { *#v }
}
Lam(x, t, b) => {
let t = dhall_to_tokenstream_bx(t, ctx);
let b = dhall_to_tokenstream_bx(b, &ctx.insert(x.clone(), ()));
let x = Literal::string(&x.clone().into());
quote! { Lam(#x.into(), #t, #b) }
}
App(f, a) => {
let f = dhall_to_tokenstream_bx(f, ctx);
let a = dhall_to_tokenstream_bx(a, ctx);
quote! { App(#f, #a) }
}
Builtin(b) => {
let b = builtin_to_tokenstream(b);
quote! { Builtin(#b) }
}
BinOp(o, a, b) => {
let o = binop_to_tokenstream(o);
let a = dhall_to_tokenstream_bx(a, ctx);
let b = dhall_to_tokenstream_bx(b, ctx);
quote! { BinOp(#o, #a, #b) }
}
OptionalLit(t, es) => {
let t = option_tks(
t.as_ref()
.map(deref)
.map(|x| dhall_to_tokenstream_bx(x, ctx)),
);
let es =
vec_tks(es.into_iter().map(|x| dhall_to_tokenstream(x, ctx)));
quote! { OptionalLit(#t, #es) }
}
ListLit(t, es) => {
let t = option_tks(
t.as_ref()
.map(deref)
.map(|x| dhall_to_tokenstream_bx(x, ctx)),
);
let es =
vec_tks(es.into_iter().map(|x| dhall_to_tokenstream(x, ctx)));
quote! { ListLit(#t, #es) }
}
e => unimplemented!("{:?}", e),
}
}
// Returns an expression of type Box<Expr<_, _>>
fn dhall_to_tokenstream_bx<L: StringLike>(
expr: &Expr<L, X, X>,
ctx: &Context<L, ()>,
) -> TokenStream {
use dhall_core::Expr::*;
match expr {
Var(V(s, n)) => {
match ctx.lookup(&s, *n) {
// Non-free variable; interpolates as itself
Some(()) => {
let s: String = s.clone().into();
quote! { bx(Var(V(#s.into(), #n))) }
}
// Free variable; interpolates as a rust variable
None => {
let s: String = s.clone().into();
// TODO: insert appropriate shifts ?
let v: TokenStream = s.parse().unwrap();
quote! { {
let x: Box<Expr<_, _, _>> = #v.clone();
x
} }
}
}
}
e => bx(dhall_to_tokenstream(e, ctx)),
}
}
fn builtin_to_tokenstream(b: &Builtin) -> TokenStream {
format!("{:?}", b).parse().unwrap()
}
fn binop_to_tokenstream(b: &BinOp) -> TokenStream {
format!("{:?}", b).parse().unwrap()
}
fn deref<T>(x: &Box<T>) -> &T {
&*x
}
fn bx(x: TokenStream) -> TokenStream {
quote! { bx(#x) }
}
fn option_tks(x: Option<TokenStream>) -> TokenStream {
match x {
Some(x) => quote! { Some(#x) },
None => quote! { None },
}
}
fn vec_tks<T>(x: T) -> TokenStream
where
T: Iterator<Item = TokenStream>,
{
quote! { vec![ #(#x),* ] }
}
|
