assign7 tweak

[lambda.git] / week9.mdwn

diff --git a/week9.mdwn b/week9.mdwn
index 2e80250..dac311c 100644 (file)
--- a/week9.mdwn
+++ b/week9.mdwn
@@ -326,7 +326,7 @@ Similarly:
 Let's consider how to interpet our new syntactic forms `newref`, `deref`, and `setref`:
 
 
 Let's consider how to interpet our new syntactic forms `newref`, `deref`, and `setref`:
 
 

-1.     \[[newref starting_val]] should allocate a new reference cell in the store and insert `starting_val` into that cell. It should return some "key" or "index" or "pointer" to the newly created reference cell, so that we can do things like:
+1.     When `expr` evaluates to `starting_val`, **newref expr** should allocate a new reference cell in the store and insert `starting_val` into that cell. It should return some "key" or "index" or "pointer" to the newly created reference cell, so that we can do things like:

 
                let ycell = newref 1
                in ...
 
                let ycell = newref 1
                in ...


@@ -351,7 +351,7 @@ Let's consider how to interpet our new syntactic forms `newref`, `deref`, and `s
                                in (Index new_index, s'')
                        ... 
 
                                in (Index new_index, s'')
                        ... 
 

-2.     When `expr` evaluates to a `store_index`, then `deref expr` should evaluate to whatever value is at that index in the current store. (If `expr` evaluates to a value of another type, `deref expr` is undefined.) In this operation, we don't change the store at all; we're just reading from it. So we'll return the same store back unchanged (assuming it wasn't changed during the evaluation of `expr`).
+2.     When `expr` evaluates to a `store_index`, then **deref expr** should evaluate to whatever value is at that index in the current store. (If `expr` evaluates to a value of another type, `deref expr` is undefined.) In this operation, we don't change the store at all; we're just reading from it. So we'll return the same store back unchanged (assuming it wasn't changed during the evaluation of `expr`).

 
                let rec eval expression g s =
                        match expression with
 
                let rec eval expression g s =
                        match expression with


@@ -362,7 +362,7 @@ Let's consider how to interpet our new syntactic forms `newref`, `deref`, and `s
                                in (List.nth s' n, s')
                        ...
 
                                in (List.nth s' n, s')
                        ...
 

-3.     When `expr1` evaluates to a `store_index` and `expr2` evaluates to an `int`, then `setref expr1 expr2` should have the effect of changing the store so that the reference cell at that index now contains that `int`. We have to make a decision about what value the `setref ...` call should itself evaluate to; OCaml makes this `()` but other choices are also possible. Here I'll just suppose we've got some appropriate value in the variable `dummy`.
+3.     When `expr1` evaluates to a `store_index` and `expr2` evaluates to an `int`, then **setref expr1 expr2** should have the effect of changing the store so that the reference cell at that index now contains that `int`. We have to make a decision about what value the `setref ...` call should itself evaluate to; OCaml makes this `()` but other choices are also possible. Here I'll just suppose we've got some appropriate value in the variable `dummy`.

 
                let rec eval expression g s =
                        match expression with
 
                let rec eval expression g s =
                        match expression with