diff --git a/src/parser.rs b/src/parser.rs
index 21353c9..0d12d79 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -13,8 +13,8 @@ use nom::{
         complete::{char, space1, usize},
         streaming::one_of,
     },
-    combinator::{opt, value},
-    error::{Error, ErrorKind},
+    combinator::{opt, value, verify},
+    error::{Error, ErrorKind, ParseError},
     multi::many0,
     sequence::{delimited, preceded},
 };
@@ -46,7 +46,7 @@ fn token_parser<'a, 's, I, N>(
     parser: &Parser<'_, '_, 's, '_, N>,
 ) -> impl NomParser<I, Output = TokenVec<'s>, Error = nom::error::Error<I>>
 where
-    I: Input + AsRef<str> + for<'z> nom::Compare<&'z str>,
+    I: Input + AsRef<str> + for<'z> nom::Compare<&'z str> + Copy,
     <I as Input>::Item: AsChar,
     <I as Input>::Item: PartialEq<char>,
     N: AsRef<str> + Clone,
@@ -126,7 +126,7 @@ impl Note {
 impl VariableChange {
     fn parser<I>(variables: &[char]) -> impl Fn(I) -> IResult<I, Self>
     where
-        I: Input + AsRef<str>,
+        I: Input + AsRef<str> + Copy,
         <I as Input>::Item: AsChar,
     {
         move |i: I| {
@@ -143,7 +143,7 @@ impl<'s> Loop<'s> {
         parser: &Parser<'i, 'n, 's, 'v, N>,
     ) -> impl Fn(I) -> IResult<I, Self>
     where
-        I: Input + AsRef<str> + for<'z> nom::Compare<&'z str>,
+        I: Input + AsRef<str> + for<'z> nom::Compare<&'z str> + Copy,
         <I as Input>::Item: AsChar,
         <I as Input>::Item: PartialEq<char>,
         N: AsRef<str> + Clone,
@@ -169,7 +169,7 @@ impl<'s> Tuplet<'s> {
         parser: &Parser<'i, 'n, 's, 'v, N>,
     ) -> impl Fn(I) -> IResult<I, Self>
     where
-        I: Input + for<'z> Compare<&'z str> + AsRef<str>,
+        I: Input + for<'z> Compare<&'z str> + AsRef<str> + Copy,
         <I as Input>::Item: AsChar,
         <I as Input>::Item: PartialEq<char>,
         N: AsRef<str> + Clone,
@@ -187,7 +187,7 @@ impl<'s> Slope<'s> {
         parser: &Parser<'i, 'n, 's, 'v, N>,
     ) -> impl Fn(I) -> IResult<I, Self>
     where
-        I: Input + for<'z> Compare<&'z str> + AsRef<str>,
+        I: Input + for<'z> Compare<&'z str> + AsRef<str> + Copy,
         <I as Input>::Item: AsChar,
         <I as Input>::Item: PartialEq<char>,
         N: AsRef<str> + Clone,
@@ -214,45 +214,45 @@ impl<'s> Slope<'s> {
 }
 
 /// Will return the longest valid fasteval expression
-fn expression_parser<'a, I: Input + AsRef<str>, C: Into<char> + Ord + Display>(
+fn expression_parser<'a, I: Input + AsRef<str> + Copy, C: Into<char> + Ord + Display>(
     variables: &[C],
 ) -> impl Fn(I) -> IResult<I, Expression> {
     |input: I| {
-        let mut end_index = 0;
-        let mut current_expression = None;
-        while input.input_len() > end_index {
-            if let Some(e) = input.as_ref()[..end_index + 1]
-                .parse::<Expression>()
-                .ok()
-                .and_then(|e| {
-                    e.instruction
-                        .eval(
-                            &e.slab,
-                            &mut BTreeMap::from_iter(
-                                variables.iter().map(|v| (v.to_string(), 0.0)),
-                            ),
-                        )
-                        .ok()
-                        .is_some()
-                        .then_some(e)
-                })
-            {
-                current_expression = Some(e);
-                end_index += 1;
-            } else if let Some(e) = current_expression {
-                return take(end_index).parse(input).map(|(r, _)| (r, e));
+        take_while_map(|i: I| {
+            i.as_ref().parse::<Expression>().ok().and_then(|e| {
+                e.instruction
+                    .eval(
+                        &e.slab,
+                        &mut BTreeMap::from_iter(variables.iter().map(|v| (v.to_string(), 0.0))),
+                    )
+                    .ok()
+                    .is_some()
+                    .then_some(e)
+            })
+        })
+        .parse(input)
+    }
+}
+
+pub fn take_while_map<F, I, O, Error: ParseError<I>>(
+    cond: F,
+) -> impl FnMut(I) -> IResult<I, O, Error>
+where
+    I: Input + Copy,
+    F: Fn(I) -> Option<O>,
+{
+    move |input: I| {
+        let mut len = 1usize;
+        let mut result = Err(nom::Err::Incomplete(nom::Needed::Unknown));
+        loop {
+            let new_result = take(len).map_opt(&cond).parse(input);
+            if new_result.is_err() {
+                return result;
             } else {
-                return Err(nom::Err::Failure(nom::error::Error::new(
-                    input,
-                    ErrorKind::Satisfy,
-                )));
+                result = new_result;
+                len += 1;
             }
         }
-        if let Some(e) = current_expression {
-            Ok((input, e))
-        } else {
-            Err(nom::Err::Incomplete(nom::Needed::Unknown))
-        }
     }
 }
 
@@ -261,7 +261,7 @@ mod tests {
     use nom::Parser;
 
     use crate::{
-        compiler::{Marker, Note, Silence},
+        compiler::{Marker, Note, Silence, VariableChange},
         parser::expression_parser,
     };
 
@@ -269,10 +269,13 @@ mod tests {
     fn expression_parser_test() {
         let parser = expression_parser(&['x']);
         let mut working_test_cases = vec![
-            "1",
-            "1x",
-            "56coucou", // should stop after 56 because c is not a known variable
-            "8x + 1 heille salut ça va ou quoi 46 - 5x",
+            ("1", ("", "1")),
+            ("1x", ("", "1x")),
+            ("56coucou", ("coucou", "56")), // should stop after 56 because c is not a known variable
+            (
+                "8x + 1 heille salut ça va ou quoi 46 - 5x",
+                ("heille salut ça va ou quoi 46 - 5x", "8x + 1"),
+            ),
         ];
         let mut not_working_test_cases = vec![
             "",
@@ -284,9 +287,17 @@ mod tests {
             " 1", // this too but the parser should remain dumb and not expect spaces before / after
         ];
 
-        for test in working_test_cases.drain(..) {
+        for (test, expected) in working_test_cases.drain(..) {
             let output = parser(test);
-            assert!(output.is_ok(), "result was not Ok: {output:?}");
+            if let Ok(result) = output {
+                assert_eq!(
+                    (expected.0, expected.1.parse().unwrap()),
+                    result,
+                    "case \"{test}\""
+                )
+            } else {
+                panic!("result was not Ok: {output:?}");
+            }
         }
 
         for test in not_working_test_cases.drain(..) {
@@ -368,4 +379,30 @@ mod tests {
             assert!(output.is_err(), "result was not Err: {output:?}");
         }
     }
+
+    #[test]
+    fn variable_change() {
+        let parser = |input| VariableChange::parser(&['a', 'b', 'ö']).parse(input);
+        let mut working_cases = vec![("$a5", ("", ('a', "5")))];
+        let mut not_working_cases = vec!["", "$", "$a", "$c8", "$d/1"];
+        for (test, expected) in working_cases.drain(..) {
+            let output = parser(test);
+            if let Ok(result) = output {
+                assert_eq!(
+                    (
+                        expected.0,
+                        VariableChange(expected.1.0, expected.1.1.parse().unwrap())
+                    ),
+                    result,
+                    "case \"{test}\""
+                );
+            } else {
+                panic!("result was not Ok: {output:?}");
+            }
+        }
+        for test in not_working_cases.drain(..) {
+            let output = parser(test);
+            assert!(output.is_err(), "result was not Err: {output:?}");
+        }
+    }
 }