Tidy up

docs/lectures/compilers/09_variable_enviroments.md

@@ -26,7 +26,7 @@ var z;
 var w := x * y - 2
 ```
 
-The parser will turn this into a list of AST for declarations
+The parser will turn this into a list of ASTs for declarations
 
 Then we have to use this to build a variable environment, and generate TAM code to write the values of the variables onto the stack.
 
@@ -91,7 +91,7 @@ command ::= identifier := expr
 			| begin commands end
 ```
 
-Here: `:=`, `if`, `then`, `else`, `while`, `do`, `getint`, `printint`, `begin`, `end`, `(`, `)` are terminal
+Here: `:=`, `if`, `then`, `else`, `while`, `do`, `getint`, `printint`, `begin`, `end`, `(`, `)` are terminals
 
 ```haskell
 data Command = 
@@ -134,7 +134,7 @@ func :: a -> b
 
 Note file name must start with a capital
 
-When you import a module, can can use functions defined in the module
+When you import a module, you can use functions defined in the module
 
 ```haskell
 data FileType = EXP | TAM
@@ -143,7 +143,7 @@ data Option = Trace | Run | Evaluate
 main :: IO () --input output monad
 ```
 
-this is the entry point, to compile
+This is the entry point; to compile:
 
 ```shell
 $ ghc Main.hs -o aec
@@ -161,4 +161,3 @@ stGet = S (\s -> (s,s))
 stRevise :: (st -> st) -> ST st ()
 stRevise f = stGet >>= stUpdate . f
 ```
-