diff --git a/src/instructions/mod.rs b/src/instructions/mod.rs
index 1a42239..dcd08f2 100644
--- a/src/instructions/mod.rs
+++ b/src/instructions/mod.rs
@@ -230,8 +230,13 @@ pub mod macros {
                         aux1_inputs.push(state.$aux1_stack[aux1_stack_len - n].clone());
                     }
                     for n in 1..=$aux0_arity {
-                        aux0_inputs.push(state.$aux0_stack[aux0_stack_len - $aux1_arity - n].clone());
+                        if std::any::type_name::<$aux0_type>() == std::any::type_name::<$aux1_type>() {
+                            aux0_inputs.push(state.$aux0_stack[aux0_stack_len - $aux1_arity - n].clone());
+                        } else {
+                            aux0_inputs.push(state.$aux0_stack[aux0_stack_len - n].clone());
+                        }
                     }
+                    // Stack shouldn't be the same for all three
                     for n in 1..=$fn_arity {
                         inputs.push(state.$in_stack[in_stack_len - n].clone());
                     }
diff --git a/src/instructions/vector.rs b/src/instructions/vector.rs
index 860e54f..6dd80c8 100644
--- a/src/instructions/vector.rs
+++ b/src/instructions/vector.rs
@@ -886,6 +886,70 @@ make_instruction_aux2!(
     i128
 );
 
+/// Replaces all values in a vector with respect to two ints. The first int is the search value
+/// and the second value is the one to replace.
+pub fn _replace<T>(mut vals: Vec<Vec<T>>, auxs: Vec<T>) -> Option<Vec<T>>
+where
+    T: Clone,
+    for<'a> &'a T: Eq,
+    Vec<T>: FromIterator<T>,
+{
+    let temp_vec = &mut vals[0];
+    let ret_vec: Vec<T> = temp_vec
+        .iter()
+        .map(|x| {
+            if x == &auxs[0] {
+                auxs[1].clone()
+            } else {
+                x.clone()
+            }
+        })
+        .collect();
+    Some(ret_vec)
+}
+make_instruction_aux!(vector_int, vector_int, _replace, Vec<i128>, 1, int, 2, i128);
+make_instruction_aux!(
+    vector_float,
+    vector_float,
+    _replace,
+    Vec<Decimal>,
+    1,
+    float,
+    2,
+    Decimal
+);
+make_instruction_aux!(
+    vector_string,
+    vector_string,
+    _replace,
+    Vec<Vec<char>>,
+    1,
+    string,
+    2,
+    Vec<char>
+);
+make_instruction_aux!(
+    vector_boolean,
+    vector_boolean,
+    _replace,
+    Vec<bool>,
+    1,
+    boolean,
+    2,
+    bool
+);
+make_instruction_aux!(
+    vector_char,
+    vector_char,
+    _replace,
+    Vec<char>,
+    1,
+    char,
+    2,
+    char
+);
+make_instruction_aux!(string, string, _replace, Vec<char>, 1, char, 2, char);
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -1331,6 +1395,26 @@ mod tests {
         vector_int_set_nth(&mut test_state);
         assert_eq!(vec![vec![0, 99, 1, 2, 3, 4, 5]], test_state.vector_int);
 
-        // Write more tests tmo!
+        test_state.string = vec![vec!['t', 'e', 's', 't']];
+        test_state.int = vec![2];
+        test_state.char = vec!['z'];
+        string_set_nth(&mut test_state);
+        assert_eq!(vec![vec!['t', 'e', 'z', 's', 't']], test_state.string);
+
+        test_state.vector_boolean = vec![vec![true, false, true]];
+        test_state.int = vec![];
+        test_state.boolean = vec![true];
+        vector_boolean_set_nth(&mut test_state);
+        assert_eq!(vec![vec![true, false, true]], test_state.vector_boolean);
+    }
+
+    #[test]
+    fn replace_test() {
+        let mut test_state = EMPTY_STATE;
+
+        test_state.vector_int = vec![vec![0, 1, 2, 3, 4, 5, 2]];
+        test_state.int = vec![3, 2];
+        vector_int_replace(&mut test_state);
+        assert_eq!(vec![vec![0, 1, 3, 3, 4, 5, 3]], test_state.vector_int);
     }
 }
diff --git a/src/main.rs b/src/main.rs
index ab3a002..70f8924 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,4 @@
+use crate::instructions::vector::_replace;
 use crate::push::state::{EMPTY_STATE, PushState};
 use instructions::utils::NumericTrait;
 use rust_decimal::MathematicalOps;
@@ -47,8 +48,10 @@ fn main() {
 
     //let test_state = EMPTY_STATE;
     //println!("{}", test_state.int == test_state.boolean);
-    println!(
+    /*println!(
         "{}",
         std::any::type_name::<PushState>() == std::any::type_name::<PushState>()
-    );
+    );*/
+
+    let temp: Option<Vec<i128>> = _replace(vec![vec![1, 2, 3]], vec![1, 2]);
 }