Add support for variables in interpreter

src/compiler/symtab.rs

@@ -0,0 +1,27 @@
+use crate::compiler::value::Value;
+use std::collections::HashMap;
+
+#[derive(Default)]
+pub struct SymTab<'source> {
+    pub locals: HashMap<&'source str, Value>,
+    pub parent: Option<Box<SymTab<'source>>>,
+}
+
+impl<'source> SymTab<'source> {
+    pub fn get(&mut self, symbol: &str) -> &mut Value {
+        if let Some(val) = self.locals.get_mut(symbol) {
+            val
+        } else if let Some(parent) = &mut self.parent {
+            parent.get(symbol)
+        } else {
+            panic!("No symbol {} found!", symbol);
+        }
+    }
+
+    pub fn new_global() -> SymTab<'source> {
+        SymTab {
+            locals: HashMap::new(),
+            parent: None,
+        }
+    }
+}