Mise en place formelle du visiteur et séparation de l'affichage d'un arbre syntaxique abstrait (AST).

src/astprinter.rs

@@ -0,0 +1,42 @@
+use crate::expr::{Binary, Expr, ExprVisitor, Grouping, Literal, Unary, VisitableExpr};
+
+pub struct ASTPrinter;
+
+impl ExprVisitor for ASTPrinter {
+    fn visit_binary(&self, b: &Binary) {
+        print!("( {}", b.operator.literal);
+        b.left.accept(self);
+        b.right.accept(self);
+        print!(")");
+    }
+
+    fn visit_grouping(&self, g: &Grouping) {
+        print!("( group ");
+        g.expression.accept(self);
+        print!(")");
+    }
+
+    fn visit_literal(&self, l: &Literal) {
+        match l {
+            Literal::LiteralNumber(i) => print!("{}", i),
+            Literal::LiteralString(s) => print!("{}", s),
+            Literal::LiteralBool(b) => print!("{}", b),
+            Literal::LiteralNil => print!("nil"),
+        }
+    }
+
+    fn visit_unary(&self, u: &Unary) {
+        print!("( {}", u.operator.literal);
+        u.right.accept(self);
+        print!(")");
+    }
+
+    fn visit_expr(&self, e: &Expr) {
+        match e {
+            Expr::BinaryExpr(b) => { b.accept(self); }
+            Expr::GroupingExpr(g) => { g.accept(self); }
+            Expr::LiteralExpr(l) => { l.accept(self); }
+            Expr::UnaryExpr(u) => { u.accept(self); }
+        }
+    }
+}