Beginnings of EMCAScript code generator

rust/src/emitter.rs

@@ -0,0 +1,72 @@
+use std::io::Write;
+use std::collections::HashSet;
+
+use crate::parser;
+
+pub struct LexicalContext<'a> {
+    parent: Option<&'a LexicalContext<'a>>,
+    local: HashSet<String>
+}
+
+impl <'a> LexicalContext<'a> {
+    pub fn toplevel() -> Self {
+	LexicalContext {
+	    parent: None,
+	    local: HashSet::new()
+	}
+    }
+    #[allow(dead_code)]
+    fn new(parent: &'a LexicalContext<'a>) -> Self {
+	LexicalContext {
+	    parent: Some(parent),
+	    local: HashSet::new(),
+	}
+    }
+    fn contains(&self, s: &str) -> bool {
+	self.local.contains(s) || self.parent.map_or(false, |c| c.contains(s))
+    }
+    fn insert(&mut self, s: String) -> bool {
+	self.local.insert(s)
+    }
+}
+
+pub fn emit_all(w: &mut dyn Write, ast: &Vec<parser::Stmt>, ctx: &mut LexicalContext) -> std::io::Result<()> {
+    for stmt in ast {
+	emit(w, stmt, ctx)?;
+    }
+    Ok(())
+}
+
+pub fn emit(w: &mut dyn Write, stmt: &parser::Stmt, ctx: &mut LexicalContext) -> std::io::Result<()> {
+    match &stmt {
+	parser::Stmt::ReplPrint(expr) => {
+	    write!(w, "console.log((")?;
+	    emit_expr(w, expr, ctx)?;
+	    writeln!(w, "));")?;
+	}
+	parser::Stmt::Assignment(id, expr) => {
+	    if !ctx.contains(id) {
+		ctx.insert(id.clone());
+		write!(w, "let ")?;
+	    }
+	    write!(w, "{} = ", id)?;
+	    emit_expr(w, expr, ctx)?;
+	    writeln!(w, ";")?;
+	}
+	_ => todo!(),
+    }
+    Ok(())
+}
+
+pub fn emit_expr(w: &mut dyn Write, expr: &parser::Expr, ctx: &mut LexicalContext) -> std::io::Result<()> {
+    match &expr {
+	parser::Expr::Id(id) => {
+	    write!(w, "{}", id)?;
+	}
+	parser::Expr::Atom(atom) => {
+	    write!(w, "{}", atom)?;
+	}
+	_ => todo!(),
+    }
+    Ok(())
+}

rust/src/main.rs

@@ -1,5 +1,6 @@
 mod parser;
 mod evaluator;
+mod emitter;
 
 use clap::Parser;
 
@@ -15,17 +16,23 @@ struct Cli {
     file: Option<PathBuf>,
     #[clap(short, long, help="Only parse, do not evaluate")]
     parse_only: bool,
+    #[clap(short, long, help="Cross-compile to ECMAScript")]
+    ecmascript: bool,
 }
 
 fn repl(cli: &Cli) {
     let mut global = evaluator::Env::global();
+    let mut toplevel = emitter::LexicalContext::toplevel();
+    let mut out = io::stdout();
     loop {
         let mut line = String::new();
         io::stdin().read_line(&mut line).unwrap();
         let tree = parser::parse_stmt(&line);
         if cli.parse_only {
             println!("{:#?}", tree);
-        } else {
+        } else if cli.ecmascript {
+	    emitter::emit(&mut out, &tree, &mut toplevel).ok();
+	} else {
             evaluator::eval(&tree, &mut global);
         }
     }
@@ -38,6 +45,10 @@ fn script(cli: &Cli) {
     let tree = parser::parse(&prgm);
     if cli.parse_only {
         println!("{:#?}", tree);
+    } else if cli.ecmascript {
+	let mut out = io::stdout();
+	let mut toplevel = emitter::LexicalContext::toplevel();
+	emitter::emit_all(&mut out, &tree, &mut toplevel).ok();
     } else {
         todo!();
     }