diff --git a/benchmarks/src/lib.rs b/benchmarks/src/lib.rs
index 847bdda..4a40a0e 100644
--- a/benchmarks/src/lib.rs
+++ b/benchmarks/src/lib.rs
@@ -4,10 +4,13 @@
 #[allow(unused_imports)]
 use parsing::suggestions::split_function_chars;
 
+#[allow(unused_imports)]
+use std::time::Duration;
 use std::{fs::File, os::raw::c_int, path::Path};
 
 use criterion::profiler::Profiler;
-use criterion::Criterion;
+#[allow(unused_imports)]
+use criterion::{BenchmarkId, Criterion};
 use criterion_macro::criterion;
 use pprof::ProfilerGuard;
 
@@ -47,8 +50,11 @@ impl<'a> Profiler for FlamegraphProfiler<'a> {
 	}
 }
 
+#[allow(dead_code)] // this infact IS used by benchmarks
 fn custom_criterion() -> Criterion {
-	Criterion::default().with_profiler(FlamegraphProfiler::new(100))
+	Criterion::default()
+		// .with_profiler(FlamegraphProfiler::new(100))
+		.warm_up_time(Duration::from_millis(250))
 }
 
 #[criterion(custom_criterion())]
@@ -71,11 +77,17 @@ fn split_function_bench(c: &mut Criterion) {
 	.map(|a| a.chars().collect::<Vec<char>>())
 	.collect::<Vec<Vec<char>>>();
 
-	c.bench_function("split_function", |b| {
-		b.iter(|| {
-			data_chars.iter().for_each(|a| {
-				split_function_chars(a);
-			})
-		})
-	});
+	let mut group = c.benchmark_group("split_function");
+	for entry in data_chars {
+		group.bench_with_input(
+			BenchmarkId::new("split_function", entry.iter().collect::<String>()),
+			&entry,
+			|b, i| {
+				b.iter(|| {
+					split_function_chars(i);
+				})
+			},
+		);
+	}
+	group.finish();
 }
diff --git a/parsing/src/parsing.rs b/parsing/src/parsing.rs
index 81c072d..1331bf8 100644
--- a/parsing/src/parsing.rs
+++ b/parsing/src/parsing.rs
@@ -129,22 +129,10 @@ fn prettyify_function_str(func: &str) -> String {
 }
 
 pub const VALID_VARIABLES: [char; 5] = ['x', 'X', 'e', 'E', 'π'];
-const LETTERS: [char; 52] = [
-	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
-	't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
-	'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
-];
-const NUMBERS: [char; 10] = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'];
 
 #[inline]
 pub fn is_variable(c: &char) -> bool { VALID_VARIABLES.contains(&c) }
 
-#[inline]
-pub fn is_letter(c: &char) -> bool { LETTERS.contains(&c) }
-
-#[inline]
-pub fn is_number(c: &char) -> bool { NUMBERS.contains(&c) }
-
 /// Adds asterisks where needed in a function
 pub fn process_func_str(function_in: &str) -> String {
 	if function_in.is_empty() {
diff --git a/parsing/src/suggestions.rs b/parsing/src/suggestions.rs
index 4aa3adf..c542d13 100644
--- a/parsing/src/suggestions.rs
+++ b/parsing/src/suggestions.rs
@@ -1,4 +1,4 @@
-use crate::parsing::{is_letter, is_number, is_variable};
+use crate::parsing::is_variable;
 
 pub const HINT_EMPTY: Hint = Hint::Single("x^2");
 const HINT_CLOSED_PARENS: Hint = Hint::Single(")");
@@ -40,7 +40,6 @@ pub fn split_function_chars(chars: &[char]) -> Vec<String> {
 	// Buffer used to store data ready to be appended
 	let mut buffer: Vec<&char> = Vec::with_capacity(chars.len());
 
-	#[derive(Default)]
 	struct BoolSlice {
 		closing_parens: bool,
 		number: bool,
@@ -59,17 +58,25 @@ pub fn split_function_chars(chars: &[char]) -> Vec<String> {
 		fn is_number(&self) -> bool { self.number && !self.masked_num }
 	}
 
-	let mut prev_char: BoolSlice = BoolSlice::default();
+	let mut prev_char: BoolSlice = BoolSlice {
+		closing_parens: false,
+		number: false,
+		letter: false,
+		variable: false,
+		masked_num: false,
+		masked_var: false,
+		exists: false,
+	};
 
 	for c in chars {
 		// Set data about current character
 		let mut curr_c = {
-			let isnumber = is_number(c);
+			let isnumber = c.is_ascii_digit();
 			let isvariable = is_variable(c);
 			BoolSlice {
 				closing_parens: c == &')',
 				number: isnumber,
-				letter: is_letter(c),
+				letter: c.is_ascii_alphabetic(),
 				variable: isvariable,
 				masked_num: match isnumber {
 					true => prev_char.masked_num,