1 files changed, 3 insertions, 0 deletions
diff --git a/src/runtime.rs b/src/runtime.rs
index 18e8e2e..71947fe 100644
--- a/src/runtime.rs
+++ b/src/runtime.rs
@@ -368,6 +368,9 @@ pub fn process(
                 parameters,
                 expression,
             } => {
+                if symbol_table.contains_key(symbol) {
+                    return Err(format!("[runtime] symbol already defined: {}", symbol));
+                }
                 let bound_params: Vec<(ast::Symbol, usize)> = parameters
                     .iter()
                     .map(|param| (param.clone(), advance_v()))