address review comments

Author: PartiallyUntyped

book/src/development/trait_checking.md

@@ -102,10 +102,23 @@ we can implement `Borrow<[u8]>` for a hypothetical type `Foo`. Let's suppose
 that we would like to find whether our type actually implements `Borrow<[u8]>`.
 
 To do so, we can use the same `implements_trait` function as above, and supply
-a parameter type that represents `[u8]`. Since `[u8]` is a specialization of
+a type parameter that represents `[u8]`. Since `[u8]` is a specialization of
 `[T]`, we can use the  [`Ty::new_slice`][new_slice] method to create a type
-that represents `[T]` and supply `u8` as a type parameter. The following code
-demonstrates how to do this:
+that represents `[T]` and supply `u8` as a type parameter.
+To create a `ty::Ty` programmatically, we rely on `Ty::new_*` methods. These
+methods create a `TyKind` and then wrap it in a `Ty` struct. This means we
+have access to all the primitive types, such as `Ty::new_char`,
+`Ty::new_bool`, `Ty::new_int`, etc. We can also create more complex types,
+such as slices, tuples, and references out of these basic building blocks.
+
+For trait checking, it is not enough to create the types, we need to convert
+them into [GenericArg]. In rustc, a generic is an entity that the compiler
+understands and has three kinds, type, const and lifetime. By calling
+`.into()` on a constructed [Ty], we wrap the type into a generic which can
+then be used by the query system to decide whether the specialized trait
+is implemented.
+
+The following code demonstrates how to do this:
 
 ```rust
 
@@ -115,14 +128,14 @@ use rustc_span::symbol::sym;
 
 let ty = todo!("Get the `Foo` type to check for a trait implementation");
 let borrow_id = cx.tcx.get_diagnostic_item(sym::Borrow).unwrap(); // avoid unwrap in real code
-let slice_bytes = Ty::new_slice(cx.tcx, cx.tcx.types.u8);
-let generic_param = slice_bytes.into();
+let slice_of_bytes_t = Ty::new_slice(cx.tcx, cx.tcx.types.u8);
+let generic_param = slice_of_bytes_t.into();
 if implements_trait(cx, ty, borrow_id, &[generic_param]) {
     todo!("Rest of lint implementation")
 }
 ```
 
-In essence, the [`Ty`] struct allows us to create types programmatically in a
+In essence, the [Ty] struct allows us to create types programmatically in a
 representation that can be used by the compiler and the query engine. We then
 use the `rustc_middle::Ty` of the type we are interested in, and query the
 compiler to see if it indeed implements the trait we are interested in.
@@ -136,6 +149,7 @@ compiler to see if it indeed implements the trait we are interested in.
 [symbol]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/symbol/struct.Symbol.html
 [symbol_index]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_span/symbol/sym/index.html
 [TyCtxt]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html
-[`Ty`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html
+[Ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html
 [rust]: https://github.com/rust-lang/rust
 [new_slice]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html#method.new_slice
+[GenericArg]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.GenericArg.html

book/src/development/type_checking.md

@@ -125,15 +125,8 @@ the [`TypeckResults::node_type()`][node_type] method inside of bodies.
 
 ## Creating Types programmatically
 
-A common usecase for creating types programmatically is when we want to check if a type implements a trait. We have
-a section on this in the [Trait Checking](trait_checking.md) chapter, but given the importance of this topic, we will
-also cover it a bit here.
-
-When we refer to "type" in this context, we refer to `ty::Ty`. To create a `ty::Ty` programmatically, we rely on
-`Ty::new_*` methods. These methods create a `TyKind` and then wrap it in a `Ty` struct.
-
-This means we have access to all the primitive types, such as `Ty::new_char`, `Ty::new_bool`, `Ty::new_int`, etc.
-We can also create more complex types, such as slices, tuples, and references.
+A common usecase for creating types programmatically is when we want to check if a type implements a trait (see
+[Trait Checking](trait_checking.md)).
 
 Here's an example of how to create a `Ty` for a slice of `u8`, i.e. `[u8]`
 
@@ -143,6 +136,9 @@ use rustc_middle::ty::Ty;
 let ty = Ty::new_slice(cx.tcx, Ty::new_u8());
 ```
 
+In general, we rely on `Ty::new_*` methods. These methods define the basic building-blocks that the
+type-system and trait-system use to define and understand the written code.
+
 ## Useful Links
 
 Below are some useful links to further explore the concepts covered