feat(gs/achilles): Prefix top-level ascriptions with `ty` r/2294

This makes parsing less ambiguous, which is nice (we can continue to not
actually care about indentation!) and aligns nicely with `fn` for the
declaration itself.

Change-Id: Id48f064e2a1e01c5105297be355d0991b312b76d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2615
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

2 files changed, 11 insertions, 2 deletions

diff --git a/users/glittershark/achilles/ach/functions.ach b/users/glittershark/achilles/ach/functions.ach
index 0d2f07eff5..dc6e7a1f3e 100644
--- a/users/glittershark/achilles/ach/functions.ach
+++ b/users/glittershark/achilles/ach/functions.ach
@@ -1,3 +1,8 @@
+ty id : fn a -> a
 fn id x = x
+
+ty plus : fn int -> int
 fn plus (x: int) (y: int) = x + y
+
+ty main : fn -> int
 fn main = plus (id 2) 7
diff --git a/users/glittershark/achilles/src/parser/mod.rs b/users/glittershark/achilles/src/parser/mod.rs
index c7e541ce48..652b083fda 100644
--- a/users/glittershark/achilles/src/parser/mod.rs
+++ b/users/glittershark/achilles/src/parser/mod.rs
@@ -22,6 +22,7 @@ pub(crate) fn is_reserved(s: &str) -> bool {
             | "let"
             | "in"
             | "fn"
+            | "ty"
             | "int"
             | "float"
             | "bool"
@@ -115,11 +116,14 @@ named!(fun_decl(&str) -> Decl, do_parse!(
 ));
 
 named!(ascription_decl(&str) -> Decl, do_parse!(
-    name: ident
+    complete!(tag!("ty"))
+        >> multispace1
+        >> name: ident
         >> multispace0
         >> complete!(char!(':'))
         >> multispace0
         >> type_: type_
+        >> multispace0
         >> (Decl::Ascription {
             name,
             type_
@@ -199,7 +203,7 @@ mod tests {
 
     #[test]
     fn top_level_ascription() {
-        let res = test_parse!(toplevel, "id : fn a -> a");
+        let res = test_parse!(toplevel, "ty id : fn a -> a");
         assert_eq!(
             res,
             vec![Decl::Ascription {