From 005976e1ddf82b118076b17997de807b1df8f047 Mon Sep 17 00:00:00 2001
From: PaddiM8 <paddim8@pm.me>
Date: Mon, 28 Dec 2020 23:54:12 +0100
Subject: [PATCH] Prevent self-referencing variables

---
 kalk/src/parser.rs     | 4 ++++
 kalk_cli/src/output.rs | 1 +
 2 files changed, 5 insertions(+)

diff --git a/kalk/src/parser.rs b/kalk/src/parser.rs
index 026eb2d..c237f75 100644
--- a/kalk/src/parser.rs
+++ b/kalk/src/parser.rs
@@ -84,6 +84,7 @@ pub enum CalcError {
     InvalidOperator,
     InvalidUnit,
     TimedOut,
+    VariableReferencesItself,
     UnexpectedToken(TokenKind, TokenKind),
     UndefinedFn(String),
     UndefinedVar(String),
@@ -195,6 +196,9 @@ fn parse_var_decl_stmt(context: &mut Context) -> Result<Stmt, CalcError> {
     let identifier = advance(context).clone();
     advance(context); // Equal sign
     let expr = parse_expr(context)?;
+    if inverter::contains_var(&context.symbol_table, &expr, &identifier.value) {
+        return Err(CalcError::VariableReferencesItself);
+    }
 
     Ok(Stmt::VarDecl(identifier.value, Box::new(expr)))
 }
diff --git a/kalk_cli/src/output.rs b/kalk_cli/src/output.rs
index 29bb93c..ced02fb 100644
--- a/kalk_cli/src/output.rs
+++ b/kalk_cli/src/output.rs
@@ -36,6 +36,7 @@ fn print_calc_err(err: CalcError) {
         InvalidOperator => format!("Invalid operator."),
         InvalidUnit => format!("Invalid unit."),
         TimedOut => format!("Operation took too long."),
+        VariableReferencesItself => format!("Variable references itself."),
         UnexpectedToken(got, expected) => {
             format!("Unexpected token: '{:?}', expected '{:?}'.", got, expected)
         }