Implement builtin functions quote and unquote

src/builtin/string.rs

@@ -1,6 +1,7 @@
 use std::collections::BTreeMap;
 
 use super::Builtin;
+use crate::common::QuoteKind;
 use crate::units::Unit;
 use crate::value::{Number, Value};
 
@@ -26,4 +27,14 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
             _ => todo!("")
         }
     });
+    decl!(f "quote", |args, _| {
+        let s = arg!(args, 0, "string").eval();
+        match s {
+            Value::Ident(i, _) => Some(Value::Ident(i, QuoteKind::Double)),
+            _ => todo!("")
+        }
+    });
+    decl!(f "unquote", |args, _| {
+        Some(arg!(args, 0, "string").eval().unquote())
+    });
 }