diff --git a/bin/fuzz.rs b/bin/fuzz.rs
index a86ca93..57cf325 100644
--- a/bin/fuzz.rs
+++ b/bin/fuzz.rs
@@ -1,7 +1,7 @@
-use clap::Parser;
-
 use std::path::Path;
 
+use clap::Parser;
+
 #[derive(Debug, Parser)]
 #[clap(name = "fuzz", version, author, about)]
 struct FuzzCli {
diff --git a/bin/kecc.rs b/bin/kecc.rs
index 3b313fa..e534ca9 100644
--- a/bin/kecc.rs
+++ b/bin/kecc.rs
@@ -1,18 +1,16 @@
-use clap::Parser;
-
 use std::ffi::OsStr;
 use std::io::Write;
 use std::os::unix::io::{FromRawFd, IntoRawFd};
 use std::path::Path;
 use std::process::{Command, Stdio};
 
-use lang_c::ast::TranslationUnit;
-use tempfile::tempdir;
-
+use clap::Parser;
 use kecc::{
     ir, ok_or_exit, write, Asmgen, Deadcode, Gvn, IrParse, IrVisualizer, Irgen, Mem2reg, Optimize,
     Parse, SimplifyCfg, Translate, O1,
 };
+use lang_c::ast::TranslationUnit;
+use tempfile::tempdir;
 
 #[derive(Debug, Parser)]
 #[clap(name = "kecc", version, author, about)]
diff --git a/src/asm/mod.rs b/src/asm/mod.rs
index 7855c14..f3eef13 100644
--- a/src/asm/mod.rs
+++ b/src/asm/mod.rs
@@ -1,10 +1,10 @@
 mod write_asm;
 
-use crate::ir;
-
 use core::convert::TryFrom;
 use core::fmt;
 
+use crate::ir;
+
 /// An assembly file.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Asm {
diff --git a/src/asmgen/mod.rs b/src/asmgen/mod.rs
index 121b42c..b28c71f 100644
--- a/src/asmgen/mod.rs
+++ b/src/asmgen/mod.rs
@@ -1,15 +1,24 @@
-use crate::asm;
-use crate::ir;
-use crate::Translate;
+use std::collections::{HashMap, HashSet, VecDeque};
 
-#[derive(Default, Clone, Copy, Debug)]
+use lang_c::ast;
+
+use crate::ir::HasDtype;
+use crate::{asm, ir, Translate};
+
+#[derive(Debug)]
 pub struct Asmgen {}
 
+impl Default for Asmgen {
+    fn default() -> Self {
+        todo!()
+    }
+}
+
 impl Translate<ir::TranslationUnit> for Asmgen {
     type Target = asm::Asm;
     type Error = ();
 
-    fn translate(&mut self, _source: &ir::TranslationUnit) -> Result<Self::Target, Self::Error> {
-        todo!("Homework: Assembly Generation")
+    fn translate(&mut self, source: &ir::TranslationUnit) -> Result<Self::Target, Self::Error> {
+        todo!()
     }
 }
diff --git a/src/c/parse.rs b/src/c/parse.rs
index b38e998..16e4550 100644
--- a/src/c/parse.rs
+++ b/src/c/parse.rs
@@ -8,14 +8,14 @@ use lang_c::span::Node;
 use crate::utils::AssertSupported;
 use crate::Translate;
 
-/// TODO(document)
+/// Parse Error
 #[derive(Debug)]
 pub enum Error {
     ParseError(ParseError),
     Unsupported,
 }
 
-/// TODO(document)
+/// C file Parser.
 #[derive(Default, Clone, Copy, Debug)]
 pub struct Parse;
 
diff --git a/src/c/write_c.rs b/src/c/write_c.rs
index e6e1e62..b7eeb1a 100644
--- a/src/c/write_c.rs
+++ b/src/c/write_c.rs
@@ -1,9 +1,8 @@
+use std::io::{Result, Write};
+
 use lang_c::ast::*;
 use lang_c::span::Node;
 
-use core::ops::Deref;
-use std::io::{Result, Write};
-
 use crate::write_base::*;
 
 impl<T: WriteLine> WriteLine for Node<T> {
@@ -19,8 +18,8 @@ impl<T: WriteString> WriteString for Node<T> {
 }
 
 impl WriteLine for TranslationUnit {
-    fn write_line(&self, _indent: usize, _write: &mut dyn Write) -> Result<()> {
-        todo!("Homework: write C")
+    fn write_line(&self, indent: usize, write: &mut dyn Write) -> Result<()> {
+        todo!()
     }
 }
 
diff --git a/src/ir/dtype.rs b/src/ir/dtype.rs
index 18d1f27..1d89086 100644
--- a/src/ir/dtype.rs
+++ b/src/ir/dtype.rs
@@ -1,13 +1,13 @@
 use core::convert::TryFrom;
 use core::fmt;
 use core::ops::Deref;
-use lang_c::ast;
-use lang_c::span::Node;
 use std::collections::{HashMap, HashSet};
 use std::hash::Hash;
-use thiserror::Error;
 
 use itertools::izip;
+use lang_c::ast;
+use lang_c::span::Node;
+use thiserror::Error;
 
 use crate::ir::*;
 use crate::some_or;
diff --git a/src/ir/interp.rs b/src/ir/interp.rs
index 3db7df4..c51412b 100644
--- a/src/ir/interp.rs
+++ b/src/ir/interp.rs
@@ -1,11 +1,9 @@
-use core::fmt;
-use core::iter;
-use core::mem;
-use ordered_float::OrderedFloat;
+use core::{fmt, iter, mem};
 use std::collections::HashMap;
-use thiserror::Error;
 
 use itertools::izip;
+use ordered_float::OrderedFloat;
+use thiserror::Error;
 
 use crate::ir::*;
 use crate::*;
@@ -410,10 +408,12 @@ impl<'i> StackFrame<'i> {
 }
 
 mod calculator {
+    use std::cmp::Ordering;
+
+    use lang_c::ast;
+
     use super::Value;
     use crate::ir::*;
-    use lang_c::ast;
-    use std::cmp::Ordering;
 
     fn calculate_integer_binary_operator_expression(
         op: &ast::BinaryOperator,
diff --git a/src/ir/mod.rs b/src/ir/mod.rs
index 2617bd1..e32c262 100644
--- a/src/ir/mod.rs
+++ b/src/ir/mod.rs
@@ -10,15 +10,15 @@ mod write_ir;
 use core::convert::TryFrom;
 use core::fmt;
 use core::ops::{Deref, DerefMut};
-use hexf_parse::{parse_hexf32, parse_hexf64};
-use itertools::Itertools;
-use lang_c::ast;
-use ordered_float::OrderedFloat;
 use std::collections::{BTreeMap, HashMap};
 use std::hash::{Hash, Hasher};
 
 pub use dtype::{Dtype, DtypeError, HasDtype};
+use hexf_parse::{parse_hexf32, parse_hexf64};
 pub use interp::{interp, Value};
+use itertools::Itertools;
+use lang_c::ast;
+use ordered_float::OrderedFloat;
 pub use parse::Parse;
 pub use visualize::Visualizer;
 
diff --git a/src/ir/parse.rs b/src/ir/parse.rs
index 9fa6ed4..e4aafc2 100644
--- a/src/ir/parse.rs
+++ b/src/ir/parse.rs
@@ -5,8 +5,7 @@ use lang_c::*;
 
 use crate::ir::*;
 use crate::utils::AssertSupported;
-use crate::Translate;
-use crate::*;
+use crate::{Translate, *};
 
 peg::parser! {
     grammar ir_parse() for str {
diff --git a/src/ir/visualize.rs b/src/ir/visualize.rs
index 0c3ac85..6ea095f 100644
--- a/src/ir/visualize.rs
+++ b/src/ir/visualize.rs
@@ -3,8 +3,7 @@
 use std::collections::HashMap;
 
 use crate::ir::*;
-use crate::some_or;
-use crate::Translate;
+use crate::{some_or, Translate};
 
 #[derive(Default, Debug)]
 pub struct Visualizer {
diff --git a/src/ir/write_ir.rs b/src/ir/write_ir.rs
index 766ddb4..77c1777 100644
--- a/src/ir/write_ir.rs
+++ b/src/ir/write_ir.rs
@@ -1,7 +1,6 @@
-use crate::ir::*;
-
 use std::io::{Result, Write};
 
+use crate::ir::*;
 use crate::write_base::*;
 use crate::*;
 
diff --git a/src/irgen/mod.rs b/src/irgen/mod.rs
index 1a2e798..a7746c4 100644
--- a/src/irgen/mod.rs
+++ b/src/irgen/mod.rs
@@ -34,23 +34,22 @@
 //! [irgen-stmt-1]: https://youtu.be/jFahkyxm994
 //! [irgen-stmt-2]: https://youtu.be/UkaXaNw462U
 //! [github-qna-irgen]: https://github.com/kaist-cp/cs420/labels/homework%20-%20irgen
-#![allow(dead_code)]
+use core::cmp::Ordering;
 use core::convert::TryFrom;
-use core::fmt;
-use core::mem;
+use core::{fmt, mem};
 use std::collections::{BTreeMap, HashMap};
 use std::ops::Deref;
 
+use itertools::izip;
 use lang_c::ast::*;
 use lang_c::driver::Parse;
 use lang_c::span::Node;
 use thiserror::Error;
 
 use crate::ir::{DtypeError, HasDtype, Named};
+use crate::write_base::WriteString;
 use crate::*;
 
-use itertools::izip;
-
 #[derive(Debug)]
 pub struct IrgenError {
     pub code: String,
@@ -69,6 +68,9 @@ impl fmt::Display for IrgenError {
     }
 }
 
+/// Error format when a compiler error happens.
+///
+/// Feel free to add more kinds of errors.
 #[derive(Debug, PartialEq, Eq, Error)]
 pub enum IrgenErrorMessage {
     /// For uncommon error
@@ -89,11 +91,17 @@ pub enum IrgenErrorMessage {
     RequireLvalue { message: String },
 }
 
+/// A C file going through IR generation.
 #[derive(Default, Debug)]
 pub struct Irgen {
+    /// Declarations made in the C file (e.g, global variables and functions)
     decls: BTreeMap<String, ir::Declaration>,
+    /// Type definitions made in the C file (e.g, typedef my_type = int;)
     typedefs: HashMap<String, ir::Dtype>,
+    /// Structs defined in the C file,
+    // TODO: explain how to use this.
     structs: HashMap<String, Option<ir::Dtype>>,
+    /// Temporary counter for anonymous structs. One should not need to use this any more.
     struct_tempid_counter: usize,
 }
 
@@ -112,14 +120,14 @@ impl Translate<TranslationUnit> for Irgen {
 
     fn translate(&mut self, source: &TranslationUnit) -> Result<Self::Target, Self::Error> {
         for ext_decl in &source.0 {
-            match ext_decl.node {
-                ExternalDeclaration::Declaration(ref var) => {
+            match &ext_decl.node {
+                ExternalDeclaration::Declaration(var) => {
                     self.add_declaration(&var.node)?;
                 }
                 ExternalDeclaration::StaticAssert(_) => {
                     panic!("ExternalDeclaration::StaticAssert is unsupported")
                 }
-                ExternalDeclaration::FunctionDefinition(ref func) => {
+                ExternalDeclaration::FunctionDefinition(func) => {
                     self.add_function_definition(&func.node)?;
                 }
             }
@@ -513,9 +521,10 @@ impl IrgenFunc<'_> {
     }
 
     /// Create a new allocation with type given by `alloc`.
-    fn insert_alloc(&mut self, alloc: Named<ir::Dtype>) -> usize {
+    fn insert_alloc(&mut self, alloc: Named<ir::Dtype>) -> ir::RegisterId {
         self.allocations.push(alloc);
-        self.allocations.len() - 1
+        let id = self.allocations.len() - 1;
+        ir::RegisterId::local(id)
     }
 
     /// Insert a new block `context` with exit instruction `exit`.
@@ -551,6 +560,7 @@ impl IrgenFunc<'_> {
     /// Panics if there are no scopes to exit, i.e, the function has a unmatched `}`.
     fn exit_scope(&mut self) {
         let _unused = self.symbol_table.pop().unwrap();
+        debug_assert!(!self.symbol_table.is_empty())
     }
 
     /// Inserts `var` with `value` to the current symbol table.
@@ -576,15 +586,15 @@ impl IrgenFunc<'_> {
     /// `bid_continue` and break block `bid_break`.
     fn translate_stmt(
         &mut self,
-        _stmt: &Statement,
-        _context: &mut Context,
-        _bid_continue: Option<ir::BlockId>,
-        _bid_break: Option<ir::BlockId>,
+        stmt: &Statement,
+        context: &mut Context,
+        bid_continue: Option<ir::BlockId>,
+        bid_break: Option<ir::BlockId>,
     ) -> Result<(), IrgenError> {
-        todo!("Homework: IR Generation")
+        todo!()
     }
 
-    /// Translate parameter declaration of the functions to IR.
+    /// Translate initial parameter declarations of the functions to IR.
     ///
     /// For example, given the following C function from [`foo.c`][foo]:
     ///
@@ -610,9 +620,11 @@ impl IrgenFunc<'_> {
     ///     %b0:p0:i32:x
     ///     %b0:p1:i32:y
     ///     %b0:p2:i32:z
+    ///   ...
     /// ```
     ///
     /// With the following arguments :
+    ///
     /// ```ignore
     /// signature = FunctionSignature { ret: ir::INT, params: vec![ir::INT, ir::INT, ir::INT] }
     /// bid_init = 0
@@ -638,6 +650,7 @@ impl IrgenFunc<'_> {
     ///     %b0:i0:unit = store %b0:p0:i32 %l0:i32*
     ///     %b0:i1:unit = store %b0:p1:i32 %l1:i32*
     ///     %b0:i2:unit = store %b0:p2:i32 %l2:i32*
+    ///   ...
     /// ```
     ///
     /// In particular, note that it is added to the local allocation list and store them to the
@@ -649,12 +662,12 @@ impl IrgenFunc<'_> {
     /// [foo]: https://github.com/kaist-cp/kecc-public/blob/main/examples/c/foo.c
     fn translate_parameter_decl(
         &mut self,
-        _signature: &ir::FunctionSignature,
-        _bid_init: ir::BlockId,
-        _name_of_params: &[String],
-        _context: &mut Context,
+        signature: &ir::FunctionSignature,
+        bid_init: ir::BlockId,
+        name_of_params: &[String],
+        context: &mut Context,
     ) -> Result<(), IrgenErrorMessage> {
-        todo!("Homework: IR Generation")
+        todo!()
     }
 }
 
diff --git a/src/lib.rs b/src/lib.rs
index 74979dc..68fec8b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,45 +5,50 @@
 #![deny(warnings)]
 // Tries to deny all rustc allow lints.
 // <https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html>
-#![deny(absolute_paths_not_starting_with_crate)]
-// Old, historical lint
-// #![deny(box_pointers)]
-#![deny(elided_lifetimes_in_paths)]
-#![deny(explicit_outlives_requirements)]
-#![deny(keyword_idents)]
-#![deny(let_underscore_drop)]
-#![deny(macro_use_extern_crate)]
-#![deny(meta_variable_misuse)]
-#![deny(missing_abi)]
-#![deny(missing_copy_implementations)]
-#![deny(missing_debug_implementations)]
-// TODO
-// #![deny(missing_docs)]
-#![deny(non_ascii_idents)]
-#![deny(noop_method_call)]
-#![deny(rust_2021_incompatible_closure_captures)]
-#![deny(rust_2021_incompatible_or_patterns)]
-#![deny(rust_2021_prefixes_incompatible_syntax)]
-#![deny(rust_2021_prelude_collisions)]
-// Necessary for skeleton code.
-// #![deny(single_use_lifetimes)]
-#![deny(trivial_casts)]
-#![deny(trivial_numeric_casts)]
-// Necessary for skeleton code.
-// #![deny(unreachable_pub)]
-#![deny(unsafe_code)]
-#![deny(unsafe_op_in_unsafe_fn)]
-#![deny(unstable_features)]
-// Necessary for `build-bin` trick.
-// #![deny(unused_crate_dependencies)]
-#![deny(unused_extern_crates)]
-#![deny(unused_import_braces)]
-#![deny(unused_lifetimes)]
-#![deny(unused_macro_rules)]
-#![deny(unused_qualifications)]
-#![deny(unused_results)]
-// Allowed for more flexible variants.
-// #![deny(variant_size_differences)]
+#![deny(
+    absolute_paths_not_starting_with_crate,
+    // Old, historical lint
+    // box_pointers,
+    elided_lifetimes_in_paths,
+    explicit_outlives_requirements,
+    keyword_idents,
+    let_underscore_drop,
+    macro_use_extern_crate,
+    meta_variable_misuse,
+    missing_abi,
+    // Most stuff are reasonably not copy.
+    // missing_copy_implementations,
+    missing_debug_implementations,
+    // TODO
+    // missing_docs
+    non_ascii_idents,
+    noop_method_call,
+    rust_2021_incompatible_closure_captures,
+    rust_2021_incompatible_or_patterns,
+    rust_2021_prefixes_incompatible_syntax,
+    rust_2021_prelude_collisions,
+    // Necessary for skeleton code.
+    // single_use_lifetimes,
+    trivial_casts,
+    trivial_numeric_casts,
+    // Necessary for skeleton code.
+    // unreachable_pub,
+    unsafe_code,
+    unsafe_op_in_unsafe_fn,
+    unstable_features,
+    // Necessary for `build-bin` trick.
+    // unused_crate_dependencies,
+    unused_extern_crates,
+    unused_import_braces,
+    unused_lifetimes,
+    unused_macro_rules,
+    unused_qualifications,
+    unused_results,
+    // Allowed for more flexible variants.
+    // variant_size_differences,
+)]
+// For skeleton code.
+#![allow(unused)]
 
 mod tests;
 mod utils;
@@ -57,17 +62,14 @@ mod asmgen;
 mod irgen;
 mod opt;
 
-pub use tests::*;
-pub use utils::*;
-pub use write_base::write;
-
-pub use c::Parse;
-pub use ir::Parse as IrParse;
-pub use ir::Visualizer as IrVisualizer;
-
 pub use asmgen::Asmgen;
+pub use c::Parse;
+pub use ir::{Parse as IrParse, Visualizer as IrVisualizer};
 pub use irgen::Irgen;
 pub use opt::{
     Deadcode, FunctionPass, Gvn, Mem2reg, Optimize, Repeat, SimplifyCfg, SimplifyCfgConstProp,
     SimplifyCfgEmpty, SimplifyCfgMerge, SimplifyCfgReach, O0, O1,
 };
+pub use tests::*;
+pub use utils::*;
+pub use write_base::write;
diff --git a/src/opt/deadcode.rs b/src/opt/deadcode.rs
index fbe4b3f..75b99f2 100644
--- a/src/opt/deadcode.rs
+++ b/src/opt/deadcode.rs
@@ -1,6 +1,9 @@
+use core::ops::Deref;
+use std::collections::{HashMap, HashSet};
+
 use crate::ir::*;
-use crate::opt::FunctionPass;
-use crate::*;
+use crate::opt::opt_utils::*;
+use crate::opt::*;
 
 pub type Deadcode = FunctionPass<Repeat<DeadcodeInner>>;
 
@@ -8,7 +11,7 @@ pub type Deadcode = FunctionPass<Repeat<DeadcodeInner>>;
 pub struct DeadcodeInner {}
 
 impl Optimize<FunctionDefinition> for DeadcodeInner {
-    fn optimize(&mut self, _code: &mut FunctionDefinition) -> bool {
-        todo!("Homework: Deadcode Elimination")
+    fn optimize(&mut self, code: &mut FunctionDefinition) -> bool {
+        todo!()
     }
 }
diff --git a/src/opt/gvn.rs b/src/opt/gvn.rs
index 24bbf2e..bf95e4a 100644
--- a/src/opt/gvn.rs
+++ b/src/opt/gvn.rs
@@ -1,13 +1,20 @@
-use crate::opt::FunctionPass;
-use crate::*;
+use core::ops::Deref;
+use std::collections::HashMap;
+
+use itertools::izip;
+use lang_c::ast;
+
+use crate::ir::*;
+use crate::opt::opt_utils::*;
+use crate::opt::*;
 
 pub type Gvn = FunctionPass<GvnInner>;
 
 #[derive(Default, Clone, Copy, Debug)]
 pub struct GvnInner {}
 
-impl Optimize<ir::FunctionDefinition> for GvnInner {
-    fn optimize(&mut self, _code: &mut ir::FunctionDefinition) -> bool {
-        todo!("Homework: Global Variable Numbering")
+impl Optimize<FunctionDefinition> for GvnInner {
+    fn optimize(&mut self, code: &mut FunctionDefinition) -> bool {
+        todo!()
     }
 }
diff --git a/src/opt/mem2reg.rs b/src/opt/mem2reg.rs
index 6be8097..eda5bb8 100644
--- a/src/opt/mem2reg.rs
+++ b/src/opt/mem2reg.rs
@@ -1,6 +1,9 @@
+use core::ops::{Deref, DerefMut};
+use std::collections::{BTreeMap, HashMap, HashSet};
+
 use crate::ir::*;
-use crate::opt::FunctionPass;
-use crate::*;
+use crate::opt::opt_utils::*;
+use crate::opt::*;
 
 pub type Mem2reg = FunctionPass<Mem2regInner>;
 
@@ -8,7 +11,7 @@ pub type Mem2reg = FunctionPass<Mem2regInner>;
 pub struct Mem2regInner {}
 
 impl Optimize<FunctionDefinition> for Mem2regInner {
-    fn optimize(&mut self, _code: &mut FunctionDefinition) -> bool {
-        todo!("Homework: Register Promotion")
+    fn optimize(&mut self, code: &mut FunctionDefinition) -> bool {
+        todo!()
     }
 }
diff --git a/src/opt/opt_utils.rs b/src/opt/opt_utils.rs
index 30cc45d..fd0dc2d 100644
--- a/src/opt/opt_utils.rs
+++ b/src/opt/opt_utils.rs
@@ -1,5 +1,5 @@
 //! Utilities for implementing optimizations.
 //!
-//! You can add here utilities commonly used in the implementation of multiple optimizations.
+//! You can freely add utilities commonly used in the implementation of multiple optimizations here.
 
 #![allow(dead_code)]
diff --git a/src/opt/simplify_cfg.rs b/src/opt/simplify_cfg.rs
index 9be7c10..d1c41f9 100644
--- a/src/opt/simplify_cfg.rs
+++ b/src/opt/simplify_cfg.rs
@@ -1,6 +1,11 @@
+use std::collections::{HashMap, HashSet};
+use std::ops::Deref;
+
+use itertools::izip;
+
 use crate::ir::*;
-use crate::opt::FunctionPass;
-use crate::*;
+use crate::opt::opt_utils::*;
+use crate::opt::*;
 
 pub type SimplifyCfg = FunctionPass<
     Repeat<(
@@ -26,25 +31,25 @@ pub struct SimplifyCfgMerge {}
 pub struct SimplifyCfgEmpty {}
 
 impl Optimize<FunctionDefinition> for SimplifyCfgConstProp {
-    fn optimize(&mut self, _code: &mut FunctionDefinition) -> bool {
-        todo!("Homework: Simplify CFG")
+    fn optimize(&mut self, code: &mut FunctionDefinition) -> bool {
+        todo!()
     }
 }
 
 impl Optimize<FunctionDefinition> for SimplifyCfgReach {
-    fn optimize(&mut self, _code: &mut FunctionDefinition) -> bool {
-        todo!("Homework: Simplify CFG")
+    fn optimize(&mut self, code: &mut FunctionDefinition) -> bool {
+        todo!()
     }
 }
 
 impl Optimize<FunctionDefinition> for SimplifyCfgMerge {
-    fn optimize(&mut self, _code: &mut FunctionDefinition) -> bool {
-        todo!("Homework: Simplify CFG")
+    fn optimize(&mut self, code: &mut FunctionDefinition) -> bool {
+        todo!()
     }
 }
 
 impl Optimize<FunctionDefinition> for SimplifyCfgEmpty {
-    fn optimize(&mut self, _code: &mut FunctionDefinition) -> bool {
-        todo!("Homework: Simplify CFG")
+    fn optimize(&mut self, code: &mut FunctionDefinition) -> bool {
+        todo!()
     }
 }
diff --git a/src/tests.rs b/src/tests.rs
index c849ca5..d4b2b84 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -1,9 +1,10 @@
-use lang_c::*;
-use rand::Rng;
 use std::fs::{self, File};
 use std::io::{stderr, Read, Write};
 use std::path::Path;
 use std::process::{Command, Stdio};
+
+use lang_c::*;
+use rand::Rng;
 use tempfile::tempdir;
 use wait_timeout::ChildExt;
 
diff --git a/src/utils.rs b/src/utils.rs
index ca9422e..4088ad2 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -1,11 +1,7 @@
-use itertools::izip;
-
-use core::ops::Deref;
-
 #[macro_export]
 /// Ok or executing the given expression.
 macro_rules! ok_or {
-    ($e:expr, $err:expr) => {{
+    ($e:expr_2021, $err:expr_2021) => {{
         match $e {
             Ok(r) => r,
             Err(_) => $err,
@@ -16,7 +12,7 @@ macro_rules! ok_or {
 #[macro_export]
 /// Some or executing the given expression.
 macro_rules! some_or {
-    ($e:expr, $err:expr) => {{
+    ($e:expr_2021, $err:expr_2021) => {{
         match $e {
             Some(r) => r,
             None => $err,
@@ -27,7 +23,7 @@ macro_rules! some_or {
 #[macro_export]
 /// Ok or exiting the process.
 macro_rules! ok_or_exit {
-    ($e:expr, $code:expr) => {{
+    ($e:expr_2021, $code:expr_2021) => {{
         match $e {
             Ok(r) => r,
             Err(e) => {
@@ -41,7 +37,7 @@ macro_rules! ok_or_exit {
 #[macro_export]
 /// Ok or exiting the process.
 macro_rules! some_or_exit {
-    ($e:expr, $code:expr) => {{
+    ($e:expr_2021, $code:expr_2021) => {{
         match $e {
             Some(r) => r,
             None => ::std::process::exit($code),
@@ -49,33 +45,41 @@ macro_rules! some_or_exit {
     }};
 }
 
-/// TODO(document)
+/// Translates `S` to [`Translate::Target`].
+// TODO: Should this be in utils?
 pub trait Translate<S> {
-    /// TODO(document)
+    /// The type to translate to.
     type Target;
 
-    /// TODO(document)
+    /// The error type.
     type Error;
 
-    /// TODO(document)
+    /// Translate `source` to `Self::Target`.
     fn translate(&mut self, source: &S) -> Result<Self::Target, Self::Error>;
 }
 
-/// TODO(document)
+/// Trait to check if a type can be translated.
 pub trait AssertSupported {
-    /// TODO(document)
+    /// Assert that the type can be translated.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the type can't be translated.
+    // TODO: should return a boolean.
     fn assert_supported(&self);
 }
 
-/// TODO(document)
+/// Essentially the same as [`PartialEq`].
+///
+/// Exists to check equaility on some foreign types.
 pub trait IsEquiv {
-    /// TODO(document)
+    /// See [`PartialEq::eq`].
     fn is_equiv(&self, other: &Self) -> bool;
 }
 
 impl<T: IsEquiv> IsEquiv for Box<T> {
     fn is_equiv(&self, other: &Self) -> bool {
-        self.deref().is_equiv(other.deref())
+        (**self).is_equiv(&**other)
     }
 }
 
@@ -97,6 +101,6 @@ impl<T: IsEquiv> IsEquiv for Option<T> {
 
 impl<T: IsEquiv> IsEquiv for Vec<T> {
     fn is_equiv(&self, other: &Self) -> bool {
-        self.len() == other.len() && izip!(self, other).all(|(lhs, rhs)| lhs.is_equiv(rhs))
+        self.len() == other.len() && self.iter().zip(other).all(|(lhs, rhs)| lhs.is_equiv(rhs))
     }
 }
diff --git a/src/write_base.rs b/src/write_base.rs
index 704b25a..3d87f57 100644
--- a/src/write_base.rs
+++ b/src/write_base.rs
@@ -1,7 +1,6 @@
 use std::io::{Result, Write};
 
 /// Write `indent` number of double spaces to `write`.
-#[inline]
 pub fn write_indent(indent: usize, write: &mut dyn Write) -> Result<()> {
     write!(write, "{}", "  ".repeat(indent))
 }
@@ -9,24 +8,21 @@ pub fn write_indent(indent: usize, write: &mut dyn Write) -> Result<()> {
 /// A trait for writing a type to a `Write` stream with a new line.
 pub trait WriteLine {
     /// Write `self` to `write`, starting at `indent` number of double spaces, with a newline at the
-    /// ned.
+    /// end.
     fn write_line(&self, indent: usize, write: &mut dyn Write) -> Result<()>;
 }
 
-/// Format types to a String.
+/// Essentially the same as [`ToString`].
 ///
-/// Most cases, `fmt::Display` is used to format a type to a string. However, in some cases, we
-/// can't implement `fmt::Display` for a type as it is defined in another crate. In such cases, we
-/// can implement this trait to format the type to a string.
+/// Exists to make some foreign types into a string.
 pub trait WriteString {
-    /// Change a type into a String.
+    /// See [`ToString::to_string`].
     fn write_string(&self) -> String;
 }
 
 impl<T: WriteString> WriteString for Box<T> {
     fn write_string(&self) -> String {
-        use core::ops::Deref;
-        self.deref().write_string()
+        (**self).write_string()
     }
 }
 
@@ -36,6 +32,7 @@ impl<T: WriteString> WriteString for &T {
     }
 }
 
+// Might be useful for debugging.
 impl<T: WriteString> WriteString for Option<T> {
     fn write_string(&self) -> String {
         if let Some(this) = self {