Add GenerateAst and AstPrinter

1 files changed, 53 insertions, 0 deletions

diff --git a/src/com/craftinginterpreters/lox/AstPrinter.java b/src/com/craftinginterpreters/lox/AstPrinter.java
new file mode 100644
index 0000000..cb494f0
--- /dev/null
+++ b/src/com/craftinginterpreters/lox/AstPrinter.java
@@ -0,0 +1,53 @@
+package com.craftinginterpreters.lox;
+
+/**
+ * AstPrinter
+ */
+class AstPrinter implements Expr.Visitor<String> {
+    String print(Expr expr) {
+        return expr.accept(this);
+    }
+
+    @Override
+    public String visitBinaryExpr(Expr.Binary expr) {
+        return parenthesize(expr.operator.lexeme, expr.left, expr.right);
+    }
+
+    @Override
+    public String visitGroupingExpr(Expr.Grouping expr) {
+        return parenthesize("group", expr.expression);
+    }
+
+    @Override
+    public String visitLiteralExpr(Expr.Literal expr) {
+        if (expr.value == null)
+            return "nil";
+        return expr.value.toString();
+    }
+
+    @Override
+    public String visitUnaryExpr(Expr.Unary expr) {
+        return parenthesize(expr.operator.lexeme, expr.right);
+    }
+
+    private String parenthesize(String name, Expr... exprs) {
+        StringBuilder builder = new StringBuilder();
+
+        builder.append("(").append(name);
+        for (Expr expr : exprs) {
+            builder.append(" ");
+            builder.append(expr.accept(this));
+        }
+        builder.append(")");
+
+        return builder.toString();
+    }
+
+    public static void main(String[] args) {
+        Expr expression = new Expr.Binary(
+                new Expr.Unary(new Token(TokenType.MINUS, "-", null, 1), new Expr.Literal(123)),
+                new Token(TokenType.STAR, "*", null, 1), new Expr.Grouping(new Expr.Literal(45.67)));
+
+        System.out.println(new AstPrinter().print(expression));
+    }
+}