feat: handle punning in a non-ambiguous way

crates/lang/src/parser/lexer.rs

@@ -69,7 +69,6 @@ pub fn lexer() -> impl Parser<char, Vec<(Token, Span)>, Error = ParseError> {
         "fn" => Token::Fn,
         "if" => Token::If,
         "else" => Token::Else,
-        "then" => Token::Then,
         "is" => Token::Is,
         "let" => Token::Let,
         "opaque" => Token::Opaque,

crates/lang/src/parser/token.rs

@@ -72,7 +72,6 @@ pub enum Token {
     Trace,
     Type,
     When,
-    Then,
 }
 
 impl fmt::Display for Token {
@@ -146,7 +145,6 @@ impl fmt::Display for Token {
             Token::Todo => "todo",
             Token::Trace => "try",
             Token::Type => "type",
-            Token::Then => "then",
         };
         write!(f, "\"{}\"", s)
     }