Fix issues in typesafe interpreter article.

content/blog/typesafe_interpreter_tuples.md

@@ -30,7 +30,7 @@ impossible to manually test every possible case in our typechecker,
 but our approach of returning `Dec (a = b)` will work just fine.
 
 ### Extending The Syntax
-First, let's extend our existing language with expressions fpr
+First, let's extend our existing language with expressions for
 tuples. For simplicity, let's use pairs `(a,b)` instead of general
 `n`-element tuples. This would make typechecking less cumbersome while still
 having the interesting effect of making the number of types in our language
@@ -46,7 +46,7 @@ Our `Expr` data type, which allows ill-typed expressions, ends up as follows:
 I've highlighted the new lines. The additions consist of the `Pair` constructor, which
 represents the tuple expression `(a, b)`, and the `Fst` and `Snd` constructors,
 which represent the `fst e` and `snd e` expressions, respectively. In
-a similar vein, we extend our `SafeExpr` GADT:
+a similar manner, we extend our `SafeExpr` GADT:
 
 {{< codelines "Idris" "typesafe-interpreter/TypesafeIntrV3.idr" 41 49 "hl_lines=7 8 9" >}}
 
@@ -93,7 +93,7 @@ Lines 14 through 16 are pretty simple; in this case, we can tell at a glance
 that the two types are equal, and Idris can infer an equality proof in
 the form of `Refl`. We return this proof by writing it in a `Just`.
 Line 23 is the catch-all case for any combination of types we didn't handle.
-Any combination of types we don't handle is false, and thus, this case
+Any combination of types we don't handle is invalid, and thus, this case
 returns `Nothing`.
 
 What about lines 17 through 22? This is the case for handling the equality
@@ -131,7 +131,7 @@ we want to substitute? After all, of the following are possible:
 
 ```Idris
 PairType rt1 lt2 = PairType lt1 lt2 -- First lt1 replaced
-PairType lt1 lt2 = PairType rt1 lt2 -- Second lt2 replaced
+PairType lt1 lt2 = PairType rt1 lt2 -- Second lt1 replaced
 PairType rt1 lt2 = PairType rt1 lt2 -- Both replaced
 ```
 
@@ -147,7 +147,7 @@ t1 => PairType lt1 lt2 = PairType t1 lt2
 t1 => PairType t1 lt2 = PairType t1 lt2
 ```
 
-The highlighted function is the one we'll need to use to attain
+The second function (highlighted) is the one we'll need to use to attain
 the desired result. Since `P` is an implicit argument to `replace`,
 we can explicitly provide it with `{P=...}`, leading to the following
 line: