Metadata (tags) on Exprs

stack-cli/src/main.rs

@@ -51,6 +51,10 @@ fn main() {
     if cli.enable_all || cli.enable_scope {
       engine.add_module(stack_std::scope::module());
     }
+
+    if cli.enable_all || cli.enable_tag {
+      engine.add_module(stack_std::tag::module());
+    }
   }
 
   match cli.subcommand {
@@ -307,6 +311,10 @@ struct Cli {
   #[arg(long)]
   #[cfg(feature = "stack-std")]
   enable_scope: bool,
+  /// Enable the tag standard module.
+  #[arg(long)]
+  #[cfg(feature = "stack-std")]
+  enable_tag: bool,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Default, clap::Subcommand)]

stack-core/src/engine.rs

@@ -115,10 +115,9 @@ impl Engine {
             }
             Ok(context)
           } else {
-            context.stack_push(Expr {
-              kind: ExprKind::Error(Error::new("unknown function".into())),
-              info: None,
-            })?;
+            context.stack_push(
+              ExprKind::Error(Error::new("unknown function".into())).into(),
+            )?;
 
             Ok(context)
           }

stack-core/src/expr.rs

@@ -11,6 +11,29 @@ use crate::{lexer::Span, scope::Scope, source::Source, symbol::Symbol};
 pub struct Expr {
   pub kind: ExprKind,
   pub info: Option<ExprInfo>,
+  pub tags: HashMap<Symbol, Expr>,
+}
+
+impl Expr {
+  pub fn with_tags(mut self, tags: HashMap<Symbol, Expr>) -> Self {
+    self.tags = tags;
+    self
+  }
+
+  pub fn with_info(mut self, info: Option<ExprInfo>) -> Self {
+    self.info = info;
+    self
+  }
+}
+
+impl From<ExprKind> for Expr {
+  fn from(value: ExprKind) -> Self {
+    Self {
+      info: None,
+      kind: value,
+      tags: HashMap::new(),
+    }
+  }
 }
 
 impl PartialEq for Expr {
@@ -57,6 +80,11 @@ pub enum ExprKind {
 }
 
 impl ExprKind {
+  #[inline]
+  pub fn into_expr(self) -> Expr {
+    self.into()
+  }
+
   #[inline]
   pub const fn is_nil(&self) -> bool {
     matches!(self, Self::Nil)