Upgrade Rust to v1.50.0

src/evaluator.rs

@@ -603,7 +603,7 @@ pub fn step<'a>(term: &Term<'a>) -> Option<Term<'a>> {
 
 // This function returns whether a term is a value. Note that a neutral term (e.g., a variable) is
 // not considered a value.
-pub fn is_value<'a>(term: &Term<'a>) -> bool {
+pub fn is_value(term: &Term) -> bool {
     match term.variant {
         Type
         | Lambda(_, _, _, _)

src/term.rs

@@ -165,7 +165,7 @@ impl<'a> Display for Variant<'a> {
 
 // Convert a term to a string with surrounding parentheses, except for simple terms that cause no
 // parsing ambiguities in any context.
-fn group<'a>(term: &Term<'a>) -> String {
+fn group(term: &Term) -> String {
     match &term.variant {
         Variant::Unifier(subterm, _) => {
             // We `clone` the borrowed `subterm` to avoid holding the dynamic borrow for too long.

toast.yml

@@ -31,7 +31,7 @@ tasks:
     command: |
       set -euo pipefail
       curl https://sh.rustup.rs -sSf |
-        sh -s -- -y --default-toolchain 1.49.0
+        sh -s -- -y --default-toolchain 1.50.0
       . $HOME/.cargo/env
       rustup component add clippy
       rustup component add rustfmt