add echo function

Signed-off-by: Ava Hahn <ava@aidanis.online>

src/stl.rs

@@ -49,6 +49,16 @@ pub fn static_stdlib(syms: &mut SymTable) -> Result<(), String> {
         },
     );
 
+    syms.insert(
+        "echo".to_string(),
+        Symbol {
+            name: String::from("echo"),
+            args: Args::Infinite,
+            conditional_branches: false,
+            value: ValueType::Internal(Rc::new(_echo_callback)),
+        },
+    );
+
     syms.insert(
         "if".to_string(),
         Symbol {
@@ -90,6 +100,16 @@ pub fn dynamic_stdlib(syms: &mut SymTable) -> Result<(), String> {
     Ok(())
 }
 
+fn _echo_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
+    if ast.len() == 1 {
+        println!("{}", ast.car);
+    } else {
+        ast.circuit(&mut |arg: &Ctr| print!("{}", arg) == ());
+    }
+
+    Ok(Ctr::None)
+}
+
 fn _store_callback(ast: &Seg, syms: &mut SymTable, env_cfg: bool) -> Result<Ctr, String> {
     let is_var = ast.len() == 2;
     if let Ctr::Symbol(ref identifier) = *ast.car {