diff --git a/src/literals.rs b/src/literals.rs
index 32fb6f0..1bfafb9 100644
--- a/src/literals.rs
+++ b/src/literals.rs
@@ -1,25 +1,37 @@
-use std::ops::RangeFrom;
+use std::ops::{RangeFrom, RangeTo};
 
 use nom::{
-    bytes::complete::tag,
     character::complete::{char, one_of},
     combinator::{map_res, recognize},
     multi::{many0, many1},
     sequence::{preceded, terminated},
+    AsChar, FindToken, InputIter, InputLength, Offset, Slice
 };
 
 use crate::parser::IResult;
 
-pub fn hexadecimal(input: &str) -> IResult<&str, u64> {
+pub fn hexadecimal<'a, I>(input: I) -> IResult<I, u64>
+where
+    // TODO: ask if there is any way to avoid this hellish constraint
+    I: InputIter
+        + nom::Slice<RangeFrom<usize>>
+        + InputLength
+        + Clone
+        + Offset
+        + Into<&'a str>
+        + Slice<RangeTo<usize>>,
+    <I as InputIter>::Item: AsChar + Copy,
+    &'a str: FindToken<<I as InputIter>::Item>
+{
     map_res(
         preceded(
-            tag("h"),
+            char('h'),
             recognize(many1(terminated(
                 one_of("0123456789abcdefABCDEF"),
                 many0(char('_')),
             ))),
         ),
-        |out: &str| u64::from_str_radix(&str::replace(&out, "_", ""), 16),
+        |out: I| u64::from_str_radix(&str::replace(&out.into(), "_", ""), 16),
     )(input)
 }
 
@@ -27,12 +39,6 @@ pub fn hexadecimal(input: &str) -> IResult<&str, u64> {
 mod test {
     use super::*;
 
-    #[test]
-    fn test_dec() {
-        assert_eq!(decimal("123").unwrap().1, 123);
-        assert_eq!(decimal("0123").unwrap().1, 123);
-    }
-
     #[test]
     fn test_hex() {
         assert_eq!(hexadecimal("hfF").unwrap().1, 0xff);
diff --git a/src/main.rs b/src/main.rs
index b68eeec..d5051a9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,9 +3,9 @@ mod parser;
 mod rtlil;
 
 use nom::error::convert_error;
-use std::path::PathBuf;
 use std::fs::File;
 use std::io::prelude::*;
+use std::path::PathBuf;
 use structopt::StructOpt;
 
 #[derive(Debug, StructOpt)]
@@ -20,7 +20,9 @@ fn main() {
     let opt = Opt::from_args();
     let mut infile = File::open(opt.input).expect("could not open file");
     let mut input = String::new();
-    infile.read_to_string(&mut input).expect("error reading file");
+    infile
+        .read_to_string(&mut input)
+        .expect("error reading file");
     let input: &str = input.as_str();
     let parsed = parser::parse(&input);
     match parsed {
diff --git a/src/parser.rs b/src/parser.rs
index bfb69f2..e172098 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -16,7 +16,7 @@ type Span<'a> = LocatedSpan<&'a str>;
 // custom IResult type for VerboseError
 pub type IResult<I, O, E = VerboseError<I>> = nom::IResult<I, O, E>;
 
-use crate::literals::{hexadecimal};
+use crate::literals::hexadecimal;
 
 fn ws0<'a, F: 'a, O, E: ParseError<&'a str>>(
     inner: F,
diff --git a/src/rtlil.rs b/src/rtlil.rs
index 961b56a..2dc180c 100644
--- a/src/rtlil.rs
+++ b/src/rtlil.rs
@@ -208,23 +208,23 @@ fn lower_expression(module: &mut Module, expr: &parser::Expression) -> String {
                     let arg_b = args_resolved.next().unwrap();
                     let cell_id = module.make_genid("and");
                     builtin_binop_cell("$and", &cell_id, &arg_a, &arg_b, &output_gen_id)
-                },
+                }
                 "xor" => {
                     let arg_a = args_resolved.next().unwrap();
                     let arg_b = args_resolved.next().unwrap();
                     let cell_id = module.make_genid("xor");
                     builtin_binop_cell("$xor", &cell_id, &arg_a, &arg_b, &output_gen_id)
-                },
+                }
                 "not" => {
                     let arg_a = args_resolved.next().unwrap();
                     let cell_id = module.make_genid("not");
                     builtin_unop_cell("$not", &cell_id, &arg_a, &output_gen_id)
-                },
+                }
                 "reduce_or" => {
                     let arg_a = args_resolved.next().unwrap();
                     let cell_id = module.make_genid("reduce_or");
                     builtin_unop_cell("$reduce_or", &cell_id, &arg_a, &output_gen_id)
-                },
+                }
                 _ => todo!("unknown function"),
             };
             module.cells.push(cell);