Add "pretty" subcommand

src/main.rs

@@ -1,12 +1,14 @@
 use std::fs;
 use std::path::PathBuf;
 
+use ::pretty::{Pretty, RcAllocator};
 use chumsky::Parser as _;
 use clap::Parser;
 
 mod ast;
 mod builtin;
 mod parser;
+mod pretty;
 mod span;
 mod table;
 mod value;
@@ -14,6 +16,7 @@ mod value;
 #[derive(Parser)]
 enum Command {
     Parse { file: PathBuf },
+    Pretty { file: PathBuf },
 }
 
 #[derive(Parser)]
@@ -31,7 +34,27 @@ fn main() -> anyhow::Result<()> {
             let content = fs::read_to_string(&file)?;
             let stream = span::stream_from_str(&content);
             match parser::parser().parse(stream) {
-                Ok(lit) => println!("Successful parse: {lit:#?}"),
+                Ok(program) => println!("Successful parse: {program:#?}"),
+                Err(errs) => {
+                    println!("Parsing failed");
+                    for err in errs {
+                        println!("{err:?}");
+                    }
+                }
+            }
+        }
+        Command::Pretty { file } => {
+            let content = fs::read_to_string(&file)?;
+            let stream = span::stream_from_str(&content);
+            match parser::parser().parse(stream) {
+                Ok(program) => {
+                    println!("Successful parse");
+                    let doc = program.pretty(&RcAllocator);
+                    let mut out = vec![];
+                    doc.render(100, &mut out)?;
+                    let str = String::from_utf8(out)?;
+                    println!("{str}");
+                }
                 Err(errs) => {
                     println!("Parsing failed");
                     for err in errs {

src/pretty.rs

@@ -0,0 +1,9 @@
+use pretty::{DocAllocator, DocBuilder, Pretty};
+
+use crate::ast::Program;
+
+impl<'a, A: DocAllocator<'a>> Pretty<'a, A> for Program {
+    fn pretty(self, allocator: &'a A) -> DocBuilder<'a, A, ()> {
+        allocator.text("Hello world")
+    }
+}