Add max recursion depth check

kalk/src/errors.rs

@@ -19,6 +19,7 @@ pub enum KalkError {
     InvalidNumberLiteral(String),
     InvalidOperator,
     InvalidUnit,
+    StackOverflow,
     TimedOut,
     VariableReferencesItself,
     PiecewiseConditionsAreFalse,
@@ -61,6 +62,7 @@ impl ToString for KalkError {
             KalkError::InvalidNumberLiteral(x) => format!("Invalid number literal: '{}'.", x),
             KalkError::InvalidOperator => String::from("Invalid operator."),
             KalkError::InvalidUnit => String::from("Invalid unit."),
+            KalkError::StackOverflow => String::from("Operation recursed too deeply."),
             KalkError::TimedOut => String::from("Operation took too long."),
             KalkError::VariableReferencesItself => String::from("Variable references itself."),
             KalkError::PiecewiseConditionsAreFalse => String::from("All the conditions in the piecewise are false."),

kalk/src/interpreter.rs

@@ -9,6 +9,8 @@ use crate::symbol_table::SymbolTable;
 use crate::{as_number_or_zero, numerical};
 use crate::{float, prelude};
 
+const DEFAULT_MAX_RECURSION_DEPTH: u32 = 128;
+
 pub struct Context<'a> {
     pub symbol_table: &'a mut SymbolTable,
     angle_unit: String,
@@ -20,6 +22,8 @@ pub struct Context<'a> {
     #[cfg(not(target_arch = "wasm32"))]
     start_time: std::time::SystemTime,
     is_approximation: bool,
+    recursion_depth: u32,
+    max_recursion_depth: u32,
 }
 
 impl<'a> Context<'a> {
@@ -40,6 +44,8 @@ impl<'a> Context<'a> {
             #[cfg(not(target_arch = "wasm32"))]
             start_time: std::time::SystemTime::now(),
             is_approximation: false,
+            recursion_depth: 0,
+            max_recursion_depth: DEFAULT_MAX_RECURSION_DEPTH,
         }
     }
 
@@ -83,6 +89,7 @@ struct SumVar {
 }
 
 fn eval_stmt(context: &mut Context, stmt: &Stmt) -> Result<KalkValue, KalkError> {
+    context.recursion_depth += 1;
     match stmt {
         Stmt::VarDecl(_, _) => eval_var_decl_stmt(context, stmt),
         Stmt::FnDecl(_, _, _) => eval_fn_decl_stmt(),
@@ -506,6 +513,10 @@ pub(crate) fn eval_fn_call_expr(
 
     match stmt_definition {
         Some(Stmt::FnDecl(_, arguments, fn_body)) => {
+            if context.recursion_depth > context.max_recursion_depth {
+                return Err(KalkError::StackOverflow);
+            }
+
             if arguments.len() != expressions.len() {
                 return Err(KalkError::IncorrectAmountOfArguments(
                     arguments.len(),