Add a pretty printer.

Cargo.toml

@@ -19,6 +19,7 @@ codespan-reporting = "0.11.1"
 lalrpop-util = "^0.19.7"
 lazy_static = "^1.4.0"
 logos = "^0.12.0"
+pretty = { version = "^0.11.2", features = ["termcolor"] }
 thiserror = "^1.0.30"
 
 [build-dependencies]

src/bin.rs

@@ -5,6 +5,7 @@ use codespan_reporting::term;
 use codespan_reporting::term::termcolor::{ColorChoice, StandardStream};
 use ngr::error::Error;
 use ngr::syntax::Program;
+use pretty::{Arena, Pretty};
 use std::fs;
 
 #[derive(Parser, Debug)]
@@ -34,11 +35,20 @@ fn main() {
     let mut file_database = SimpleFiles::new();
     let initial_file_name = &args.file;
 
-    if let Err(e) = compile_file(&mut file_database, initial_file_name) {
+    match compile_file(&mut file_database, initial_file_name) {
-        let diagnostic = Diagnostic::from(e);
+        Ok(p) => {
-        let writer = StandardStream::stderr(ColorChoice::Auto);
+            let arena = Arena::new();
-        let config = codespan_reporting::term::Config::default();
+            p.pretty(&arena)
+                .into_doc()
+                .render_colored(72, StandardStream::stdout(ColorChoice::Auto))
+                .unwrap()
+        }
+        Err(e) => {
+            let diagnostic = Diagnostic::from(e);
+            let writer = StandardStream::stderr(ColorChoice::Auto);
+            let config = codespan_reporting::term::Config::default();
 
-        term::emit(&mut writer.lock(), &config, &file_database, &diagnostic).unwrap();
+            term::emit(&mut writer.lock(), &config, &file_database, &diagnostic).unwrap();
+        }
     }
 }

src/syntax/ast.rs

@@ -1,10 +1,32 @@
 use crate::syntax::token_stream::Location;
+use pretty::{DocAllocator, DocBuilder, Pretty};
+
+static BINARY_OPERATORS: &[&str] = &["+", "-", "*", "/"];
 
 #[derive(Debug, PartialEq)]
 pub struct Program {
     pub statements: Vec<Statement>,
 }
 
+impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Program
+where
+    A: 'a,
+    D: ?Sized + DocAllocator<'a, A>,
+{
+    fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
+        let mut result = allocator.nil();
+
+        for stmt in self.statements.iter() {
+            result = result
+                .append(stmt.pretty(allocator))
+                .append(allocator.text(";"))
+                .append(allocator.hardline());
+        }
+
+        result
+    }
+}
+
 #[derive(Debug, PartialEq)]
 pub enum Statement {
     Binding(Location, String, Expression),
@@ -12,6 +34,28 @@ pub enum Statement {
     Expr(Location, Expression),
 }
 
+impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Statement
+where
+    A: 'a,
+    D: ?Sized + DocAllocator<'a, A>,
+{
+    fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
+        match self {
+            Statement::Binding(_, var, expr) => allocator
+                .text(var.to_string())
+                .append(allocator.space())
+                .append(allocator.text("="))
+                .append(allocator.space())
+                .append(expr.pretty(allocator)),
+            Statement::Print(_, var) => allocator
+                .text("print")
+                .append(allocator.space())
+                .append(allocator.text(var.to_string())),
+            Statement::Expr(_, expr) => expr.pretty(allocator),
+        }
+    }
+}
+
 #[derive(Debug, PartialEq)]
 pub enum Expression {
     Value(Location, Value),
@@ -19,7 +63,79 @@ pub enum Expression {
     Primitive(Location, String, Vec<Expression>),
 }
 
+impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Expression
+where
+    A: 'a,
+    D: ?Sized + DocAllocator<'a, A>,
+{
+    fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
+        match self {
+            Expression::Value(_, val) => val.pretty(allocator),
+            Expression::Reference(_, var) => allocator.text(var.to_string()),
+            Expression::Primitive(_, op, exprs) if BINARY_OPERATORS.contains(&op.as_ref()) => {
+                assert_eq!(
+                    exprs.len(),
+                    2,
+                    "Found binary operator with {} components?",
+                    exprs.len()
+                );
+
+                let left = exprs[0].pretty(allocator);
+                let right = exprs[1].pretty(allocator);
+
+                left.append(allocator.space())
+                    .append(allocator.text(op.to_string()))
+                    .append(allocator.space())
+                    .append(right)
+                    .parens()
+            }
+            Expression::Primitive(_, op, exprs) => {
+                let call = allocator.text(op.to_string());
+                let args = exprs.iter().map(|x| x.pretty(allocator));
+                let comma_sepped_args = allocator.intersperse(args, CommaSep {});
+                call.append(comma_sepped_args.parens())
+            }
+        }
+    }
+}
+
 #[derive(Debug, PartialEq)]
 pub enum Value {
     Number(Option<u8>, i128),
 }
+
+impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Value
+where
+    A: 'a,
+    D: ?Sized + DocAllocator<'a, A>,
+{
+    fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
+        match self {
+            Value::Number(opt_base, value) => {
+                let value_str = match opt_base {
+                    None => format!("{}", value),
+                    Some(2) => format!("0b{:b}", value),
+                    Some(8) => format!("0o{:o}", value),
+                    Some(10) => format!("0d{}", value),
+                    Some(16) => format!("0x{:x}", value),
+                    Some(_) => format!("!!{:x}!!", value),
+                };
+
+                allocator.text(value_str)
+            }
+        }
+    }
+}
+
+#[derive(Clone, Copy)]
+struct CommaSep {}
+
+impl<'a, 'b, D, A> Pretty<'a, D, A> for CommaSep
+where
+    A: 'a,
+    D: ?Sized + DocAllocator<'a, A>,
+{
+    fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
+        allocator.text(",").append(allocator.space())
+    }
+}