Add TraceIfFalse untyped expression

The goal is to handle this without bothering the code generation down the line. That is, we can handle it when transforming from the untyped AST to the typed one. That's why there's no 'TraceIfFalse' constructor in the typed AST. It has disappeared during type-check.

crates/aiken-lang/src/expr.rs

@@ -382,6 +382,11 @@ pub enum UntypedExpr {
         text: Box<Self>,
     },
 
+    TraceIfFalse {
+        location: Span,
+        value: Box<Self>,
+    },
+
     When {
         location: Span,
         subjects: Vec<Self>,
@@ -510,7 +515,8 @@ impl UntypedExpr {
         match self {
             Self::PipeLine { expressions, .. } => expressions.last().location(),
             Self::Trace { then, .. } => then.location(),
-            Self::Fn { location, .. }
+            Self::TraceIfFalse { location, .. }
+            | Self::Fn { location, .. }
             | Self::Var { location, .. }
             | Self::Int { location, .. }
             | Self::ErrorTerm { location, .. }

crates/aiken-lang/src/format.rs

@@ -800,6 +800,8 @@ impl<'comments> Formatter<'comments> {
             }
 
             UntypedExpr::ErrorTerm { .. } => "error".to_doc(),
+
+            UntypedExpr::TraceIfFalse { value, .. } => self.trace_if_false(value),
         };
 
         commented(document, comments)
@@ -814,6 +816,10 @@ impl<'comments> Formatter<'comments> {
         }
     }
 
+    pub fn trace_if_false<'a>(&mut self, value: &'a UntypedExpr) -> Document<'a> {
+        docvec![self.wrap_unary_op(value), "?"]
+    }
+
     pub fn trace<'a>(
         &mut self,
         kind: &'a TraceKind,

crates/aiken-lang/src/tipo/expr.rs

@@ -225,6 +225,7 @@ impl<'a, 'b> ExprTyper<'a, 'b> {
             | UntypedExpr::TupleIndex { .. }
             | UntypedExpr::UnOp { .. }
             | UntypedExpr::Var { .. }
+            | UntypedExpr::TraceIfFalse { .. }
             | UntypedExpr::When { .. } => Ok(()),
         }
     }
@@ -361,6 +362,10 @@ impl<'a, 'b> ExprTyper<'a, 'b> {
                 value,
                 op,
             } => self.infer_un_op(location, value, op),
+
+            UntypedExpr::TraceIfFalse { value, location } => {
+                self.infer_trace_if_false(*value, location)
+            }
         }
     }