tweak calc improvements

Signed-off-by: Jim Pryor <profjim@jimpryor.net>

diff --git a/code/calculator/calc1.ml b/code/calculator/calc1.ml
index 35b32ff..554ce7c 100644 (file)
--- a/code/calculator/calc1.ml
+++ b/code/calculator/calc1.ml
@@ -1,6 +1,6 @@
 (* Original calculator from Week7, enhanced with Booleans and Immutable Pairs *)
 
 (* Original calculator from Week7, enhanced with Booleans and Immutable Pairs *)
 

-       type term =
+    type term =

       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)
       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)


@@ -12,47 +12,47 @@
     | First of term
     ;;
 
     | First of term
     ;;
 

-       type expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value;;
-       type bound_value = expressed_value;;
-       type assignment = (char * bound_value) list;;
+    type expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value;;
+    type bound_value = expressed_value;;
+    type assignment = (char * bound_value) list;;

 
 

-       let rec eval (t : term) (g : assignment) = match t with
-         Intconstant x -> Int x
-       | Multiplication (t1, t2) ->
-               (* we don't handle cases where the subterms don't evaluate to Ints *)
-               let Int i1 = eval t1 g
-               in let Int i2 = eval t2 g
-               (* Multiplication (t1, t2) should evaluate to an Int *)
-               in Int (i1 * i2)
-       | Addition (t1, t2) ->
-               let Int i1 = eval t1 g
-               in let Int i2 = eval t2 g
-               in Int (i1 + i2)
-       | Variable (var) ->
-               (* we don't handle cases where g doesn't bind var to any value *)
-               List.assoc var g
-       | Let (var_to_bind, t2, t3) ->
-               (* evaluate t3 under a new assignment where var_to_bind has been bound to
-                  the result of evaluating t2 under the current assignment *)
-               let value2 = eval t2 g
-               in let g' = (var_to_bind, value2) :: g
-               in eval t3 g'
-       | Iszero (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to an Int *)
-               let Int i1 = eval t1 g
-               (* Iszero t1 should evaluate to a Bool *)
-               in Bool (i1 = 0)
-       | If (t1, t2, t3) ->
-               (* we don't handle cases where t1 doesn't evaluate to a boolean *)
-               let Bool b1 = eval t1 g
-               in if b1 then eval t2 g
-               else eval t3 g
-       | Makepair (t1, t2) ->
-               let value1 = eval t1 g
-               in let value2 = eval t2 g
-               in Pair (value1, value2)
-       | First (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Pair *)
-               let Pair (value1, value2) = eval t1 g
-               in value1
+    let rec eval (t : term) (g : assignment) = match t with
+      Intconstant x -> Int x
+    | Multiplication (t1, t2) ->
+        (* we don't handle cases where the subterms don't evaluate to Ints *)
+        let Int i1 = eval t1 g
+        in let Int i2 = eval t2 g
+        (* Multiplication (t1, t2) should evaluate to an Int *)
+        in Int (i1 * i2)
+    | Addition (t1, t2) ->
+        let Int i1 = eval t1 g
+        in let Int i2 = eval t2 g
+        in Int (i1 + i2)
+    | Variable (var) ->
+        (* we don't handle cases where g doesn't bind var to any value *)
+        List.assoc var g
+    | Let (var_to_bind, t2, t3) ->
+        (* evaluate t3 under a new assignment where var_to_bind has been bound to
+           the result of evaluating t2 under the current assignment *)
+        let value2 = eval t2 g
+        in let g' = (var_to_bind, value2) :: g
+        in eval t3 g'
+    | Iszero (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to an Int *)
+        let Int i1 = eval t1 g
+        (* Iszero t1 should evaluate to a Bool *)
+        in Bool (i1 = 0)
+    | If (t1, t2, t3) ->
+        (* we don't handle cases where t1 doesn't evaluate to a boolean *)
+        let Bool b1 = eval t1 g
+        in if b1 then eval t2 g
+        else eval t3 g
+    | Makepair (t1, t2) ->
+        let value1 = eval t1 g
+        in let value2 = eval t2 g
+        in Pair (value1, value2)
+    | First (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Pair *)
+        let Pair (value1, value2) = eval t1 g
+        in value1

     ;;
     ;;

diff --git a/code/calculator/calc2.ml b/code/calculator/calc2.ml
index 57a3342..ef4a37c 100644 (file)
--- a/code/calculator/calc2.ml
+++ b/code/calculator/calc2.ml
@@ -1,6 +1,6 @@
 (* calc1.ml, enhanced with Function Values *)
 
 (* calc1.ml, enhanced with Function Values *)
 

-       type term =
+    type term =

       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)
       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)


@@ -15,54 +15,54 @@
     ;;
 
     type bound_value = expressed_value
     ;;
 
     type bound_value = expressed_value

-       and assignment = (char * bound_value) list
+    and assignment = (char * bound_value) list

     and expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment;;
 
     and expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment;;
 

-       let rec eval (t : term) (g : assignment) = match t with
-         Intconstant x -> Int x
-       | Multiplication (t1, t2) ->
-               (* we don't handle cases where the subterms don't evaluate to Ints *)
-               let Int i1 = eval t1 g
-               in let Int i2 = eval t2 g
-               (* Multiplication (t1, t2) should evaluate to an Int *)
-               in Int (i1 * i2)
-       | Addition (t1, t2) ->
-               let Int i1 = eval t1 g
-               in let Int i2 = eval t2 g
-               in Int (i1 + i2)
-       | Variable (var) ->
-               (* we don't handle cases where g doesn't bind var to any value *)
-               List.assoc var g
-       | Let (var_to_bind, t2, t3) ->
-               (* evaluate t3 under a new assignment where var_to_bind has been bound to
-                  the result of evaluating t1 under the current assignment *)
-               let value2 = eval t2 g
-               in let g' = (var_to_bind, value2) :: g
-               in eval t3 g'
-       | Iszero (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to an Int *)
-               let Int i1 = eval t1 g
-               (* Iszero t1 should evaluate to a Bool *)
-               in Bool (i1 = 0)
-       | If (t1, t2, t3) ->
-               (* we don't handle cases where t1 doesn't evaluate to a boolean *)
-               let Bool b1 = eval t1 g
-               in if b1 then eval t2 g
-               else eval t3 g
-       | Makepair (t1, t2) ->
-               let value1 = eval t1 g
-               in let value2 = eval t2 g
-               in Pair (value1, value2)
-       | First (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Pair *)
-               let Pair (value1, value2) = eval t1 g
-               in value1
-       | Lambda (arg_var, t2) -> Closure (arg_var, t2, g)
-       | Apply (t1, t2) ->
-               (* we don't handle cases where t1 doesn't evaluate to a function value *)
-               let Closure (arg_var, body, savedg) = eval t1 g
-               in let value2 = eval t2 g
-               (* evaluate body under savedg, except with arg_var bound to value2 *)
-               in let savedg' = (arg_var, value2) :: savedg
-               in eval body savedg'
+    let rec eval (t : term) (g : assignment) = match t with
+      Intconstant x -> Int x
+    | Multiplication (t1, t2) ->
+        (* we don't handle cases where the subterms don't evaluate to Ints *)
+        let Int i1 = eval t1 g
+        in let Int i2 = eval t2 g
+        (* Multiplication (t1, t2) should evaluate to an Int *)
+        in Int (i1 * i2)
+    | Addition (t1, t2) ->
+        let Int i1 = eval t1 g
+        in let Int i2 = eval t2 g
+        in Int (i1 + i2)
+    | Variable (var) ->
+        (* we don't handle cases where g doesn't bind var to any value *)
+        List.assoc var g
+    | Let (var_to_bind, t2, t3) ->
+        (* evaluate t3 under a new assignment where var_to_bind has been bound to
+           the result of evaluating t1 under the current assignment *)
+        let value2 = eval t2 g
+        in let g' = (var_to_bind, value2) :: g
+        in eval t3 g'
+    | Iszero (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to an Int *)
+        let Int i1 = eval t1 g
+        (* Iszero t1 should evaluate to a Bool *)
+        in Bool (i1 = 0)
+    | If (t1, t2, t3) ->
+        (* we don't handle cases where t1 doesn't evaluate to a boolean *)
+        let Bool b1 = eval t1 g
+        in if b1 then eval t2 g
+        else eval t3 g
+    | Makepair (t1, t2) ->
+        let value1 = eval t1 g
+        in let value2 = eval t2 g
+        in Pair (value1, value2)
+    | First (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Pair *)
+        let Pair (value1, value2) = eval t1 g
+        in value1
+    | Lambda (arg_var, t2) -> Closure (arg_var, t2, g)
+    | Apply (t1, t2) ->
+        (* we don't handle cases where t1 doesn't evaluate to a function value *)
+        let Closure (arg_var, body, savedg) = eval t1 g
+        in let value2 = eval t2 g
+        (* evaluate body under savedg, except with arg_var bound to value2 *)
+        in let savedg' = (arg_var, value2) :: savedg
+        in eval body savedg'

     ;;
     ;;

diff --git a/code/calculator/calc3.ml b/code/calculator/calc3.ml
index 522ca28..65bf754 100644 (file)
--- a/code/calculator/calc3.ml
+++ b/code/calculator/calc3.ml
@@ -1,6 +1,6 @@
 (* calc2.ml, enhanced with Recursive Function Values *)
 
 (* calc2.ml, enhanced with Recursive Function Values *)
 

-       type term =
+    type term =

       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)
       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)


@@ -16,67 +16,67 @@
     ;;
 
     type bound_value = Nonrecursive of expressed_value | Recursive_Closure of char * char * term * assignment
     ;;
 
     type bound_value = Nonrecursive of expressed_value | Recursive_Closure of char * char * term * assignment

-       and assignment = (char * bound_value) list
+    and assignment = (char * bound_value) list

     and expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment;;
 
     and expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment;;
 

-       let rec eval (t : term) (g : assignment) = match t with
-         Intconstant x -> Int x
-       | Multiplication (t1, t2) ->
-               (* we don't handle cases where the subterms don't evaluate to Ints *)
-               let Int i1 = eval t1 g
-               in let Int i2 = eval t2 g
-               (* Multiplication (t1, t2) should evaluate to an Int *)
-               in Int (i1 * i2)
-       | Addition (t1, t2) ->
-               let Int i1 = eval t1 g
-               in let Int i2 = eval t2 g
-               in Int (i1 + i2)
-       | Variable (var) -> (
-               (* we don't handle cases where g doesn't bind var to any value *)
-               match List.assoc var g with
+    let rec eval (t : term) (g : assignment) = match t with
+      Intconstant x -> Int x
+    | Multiplication (t1, t2) ->
+        (* we don't handle cases where the subterms don't evaluate to Ints *)
+        let Int i1 = eval t1 g
+        in let Int i2 = eval t2 g
+        (* Multiplication (t1, t2) should evaluate to an Int *)
+        in Int (i1 * i2)
+    | Addition (t1, t2) ->
+        let Int i1 = eval t1 g
+        in let Int i2 = eval t2 g
+        in Int (i1 + i2)
+    | Variable (var) -> (
+        (* we don't handle cases where g doesn't bind var to any value *)
+        match List.assoc var g with

           | Nonrecursive value -> value
           | Recursive_Closure (self_var, arg_var, body, savedg) as rec_closure ->
           | Nonrecursive value -> value
           | Recursive_Closure (self_var, arg_var, body, savedg) as rec_closure ->

-                         (* we update savedg to bind self_var to rec_closure here *)
+              (* we update savedg to bind self_var to rec_closure here *)

               let savedg' = (self_var, rec_closure) :: savedg
               in Closure (arg_var, body, savedg')
         )
               let savedg' = (self_var, rec_closure) :: savedg
               in Closure (arg_var, body, savedg')
         )

-       | Let (var_to_bind, t2, t3) ->
-               (* evaluate t3 under a new assignment where var_to_bind has been bound to
+    | Let (var_to_bind, t2, t3) ->
+        (* evaluate t3 under a new assignment where var_to_bind has been bound to

            the result of evaluating t2 under the current assignment *)
            the result of evaluating t2 under the current assignment *)

-               let value2 = eval t2 g
-               (* we have to wrap value2 in Nonrecursive *)
-               in let g' = (var_to_bind, Nonrecursive value2) :: g
-               in eval t3 g'
-       | Iszero (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to an Int *)
-               let Int i1 = eval t1 g
-               (* Iszero t1 should evaluate to a Bool *)
-               in Bool (i1 = 0)
-       | If (t1, t2, t3) ->
-               (* we don't handle cases where t1 doesn't evaluate to a boolean *)
-               let Bool b1 = eval t1 g
-               in if b1 then eval t2 g
-               else eval t3 g
-       | Makepair (t1, t2) ->
-               let value1 = eval t1 g
-               in let value2 = eval t2 g
-               in Pair (value1, value2)
-       | First (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Pair *)
-               let Pair (value1, value2) = eval t1 g
-               in value1
-       | Lambda (arg_var, t2) -> Closure (arg_var, t2, g)
-       | Apply (t1, t2) ->
-               (* we don't handle cases where t1 doesn't evaluate to a function value *)
-               let Closure (arg_var, body, savedg) = eval t1 g
-               in let value2 = eval t2 g
-               (* evaluate body under savedg, except with arg_var bound to Nonrecursive value2 *)
-               in let savedg' = (arg_var, Nonrecursive value2) :: savedg
-               in eval body savedg'
-       | Letrec (var_to_bind, t2, t3) ->
-               (* we don't handle cases where t2 doesn't evaluate to a function value *)
-               let Closure (arg_var, body, savedg) = eval t2 g
+        let value2 = eval t2 g
+        (* we have to wrap value2 in Nonrecursive *)
+        in let g' = (var_to_bind, Nonrecursive value2) :: g
+        in eval t3 g'
+    | Iszero (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to an Int *)
+        let Int i1 = eval t1 g
+        (* Iszero t1 should evaluate to a Bool *)
+        in Bool (i1 = 0)
+    | If (t1, t2, t3) ->
+        (* we don't handle cases where t1 doesn't evaluate to a boolean *)
+        let Bool b1 = eval t1 g
+        in if b1 then eval t2 g
+        else eval t3 g
+    | Makepair (t1, t2) ->
+        let value1 = eval t1 g
+        in let value2 = eval t2 g
+        in Pair (value1, value2)
+    | First (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Pair *)
+        let Pair (value1, value2) = eval t1 g
+        in value1
+    | Lambda (arg_var, t2) -> Closure (arg_var, t2, g)
+    | Apply (t1, t2) ->
+        (* we don't handle cases where t1 doesn't evaluate to a function value *)
+        let Closure (arg_var, body, savedg) = eval t1 g
+        in let value2 = eval t2 g
+        (* evaluate body under savedg, except with arg_var bound to Nonrecursive value2 *)
+        in let savedg' = (arg_var, Nonrecursive value2) :: savedg
+        in eval body savedg'
+    | Letrec (var_to_bind, t2, t3) ->
+        (* we don't handle cases where t2 doesn't evaluate to a function value *)
+        let Closure (arg_var, body, savedg) = eval t2 g

         (* evaluate t3 under a new assignment where var_to_bind has been recursively bound to that function value *) 
         (* evaluate t3 under a new assignment where var_to_bind has been recursively bound to that function value *) 

-               in let g' = (var_to_bind, Recursive_Closure (var_to_bind, arg_var, body, savedg)) :: g
-               in eval t3 g'
+        in let g' = (var_to_bind, Recursive_Closure (var_to_bind, arg_var, body, savedg)) :: g
+        in eval t3 g'

     ;;
     ;;

diff --git a/code/calculator/calc4.ml b/code/calculator/calc4.ml
index 571d277..378e037 100644 (file)
--- a/code/calculator/calc4.ml
+++ b/code/calculator/calc4.ml
@@ -1,6 +1,6 @@
 (* calc3.ml, enhanced with Mutable Cells *)
 
 (* calc3.ml, enhanced with Mutable Cells *)
 

-       type term =
+    type term =

       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)
       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)


@@ -18,101 +18,101 @@
     | Setref of (term * term)
     ;;
 
     | Setref of (term * term)
     ;;
 

-       type index = int;;
+    type index = int;;

 
     type bound_value = Nonrecursive of expressed_value | Recursive_Closure of char * char * term * assignment
 
     type bound_value = Nonrecursive of expressed_value | Recursive_Closure of char * char * term * assignment

-       and assignment = (char * bound_value) list
+    and assignment = (char * bound_value) list

     and expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment | Mutcell of index;;
 
     and expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment | Mutcell of index;;
 

-       type store = expressed_value list;;
+    type store = expressed_value list;;

 
 

-       let rec eval (t : term) (g : assignment) (s : store) = match t with
-         Intconstant x -> (Int x, s)
-       | Multiplication (t1, t2) ->
-               (* we don't handle cases where the subterms don't evaluate to Ints *)
-               let (Int i1, s') = eval t1 g s
-               in let (Int i2, s'') = eval t2 g s'
-               (* Multiplication (t1, t2) should evaluate to an Int *)
-               in (Int (i1 * i2), s'')
-       | Addition (t1, t2) ->
-               let (Int i1, s') = eval t1 g s
-               in let (Int i2, s'') = eval t2 g s'
-               in (Int (i1 + i2), s'')
-       | Variable (var) -> (
-               (* we don't handle cases where g doesn't bind var to any value *)
-               match List.assoc var g with
+    let rec eval (t : term) (g : assignment) (s : store) = match t with
+      Intconstant x -> (Int x, s)
+    | Multiplication (t1, t2) ->
+        (* we don't handle cases where the subterms don't evaluate to Ints *)
+        let (Int i1, s') = eval t1 g s
+        in let (Int i2, s'') = eval t2 g s'
+        (* Multiplication (t1, t2) should evaluate to an Int *)
+        in (Int (i1 * i2), s'')
+    | Addition (t1, t2) ->
+        let (Int i1, s') = eval t1 g s
+        in let (Int i2, s'') = eval t2 g s'
+        in (Int (i1 + i2), s'')
+    | Variable (var) -> (
+        (* we don't handle cases where g doesn't bind var to any value *)
+        match List.assoc var g with

           | Nonrecursive value -> value
           | Recursive_Closure (self_var, arg_var, body, savedg) as rec_closure ->
           | Nonrecursive value -> value
           | Recursive_Closure (self_var, arg_var, body, savedg) as rec_closure ->

-                         (* we update savedg to bind self_var to rec_closure here *)
+              (* we update savedg to bind self_var to rec_closure here *)

               let savedg' = (self_var, rec_closure) :: savedg
               in Closure (arg_var, body, savedg')
         ), s
               let savedg' = (self_var, rec_closure) :: savedg
               in Closure (arg_var, body, savedg')
         ), s

-       | Let (var_to_bind, t2, t3) ->
-               (* evaluate t3 under a new assignment where var_to_bind has been bound to
+    | Let (var_to_bind, t2, t3) ->
+        (* evaluate t3 under a new assignment where var_to_bind has been bound to

            the result of evaluating t2 under the current assignment *)
            the result of evaluating t2 under the current assignment *)

-               let (value2, s') = eval t2 g s
-               (* we have to wrap value2 in Nonrecursive *)
-               in let g' = (var_to_bind, Nonrecursive value2) :: g
-               in eval t3 g' s'
-       | Iszero (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to an Int *)
-               let (Int i1, s') = eval t1 g s
-               (* Iszero t1 should evaluate to a Bool *)
-               in (Bool (i1 = 0), s')
-       | If (t1, t2, t3) ->
-               (* we don't handle cases where t1 doesn't evaluate to a boolean *)
-               let (Bool b1, s') = eval t1 g s
+        let (value2, s') = eval t2 g s
+        (* we have to wrap value2 in Nonrecursive *)
+        in let g' = (var_to_bind, Nonrecursive value2) :: g
+        in eval t3 g' s'
+    | Iszero (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to an Int *)
+        let (Int i1, s') = eval t1 g s
+        (* Iszero t1 should evaluate to a Bool *)
+        in (Bool (i1 = 0), s')
+    | If (t1, t2, t3) ->
+        (* we don't handle cases where t1 doesn't evaluate to a boolean *)
+        let (Bool b1, s') = eval t1 g s

         (* note we thread s' through only one of the then/else clauses *)
         (* note we thread s' through only one of the then/else clauses *)

-               in if b1 then eval t2 g s'
-               else eval t3 g s'
-       | Makepair (t1, t2) ->
-               let (value1, s') = eval t1 g s
-               in let (value2, s'') = eval t2 g s'
-               in (Pair (value1, value2), s'')
-       | First (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Pair *)
-               let (Pair (value1, value2), s') = eval t1 g s
-               in (value1, s')
-       | Lambda (arg_var, t2) -> (Closure (arg_var, t2, g), s)
-       | Apply (t1, t2) ->
-               (* we don't handle cases where t1 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t1 g s
-               in let (value2, s'') = eval t2 g s'
-               (* evaluate body under savedg, except with arg_var bound to Nonrecursive value2 *)
-               in let savedg' = (arg_var, Nonrecursive value2) :: savedg
-               in eval body savedg' s''
-       | Letrec (var_to_bind, t2, t3) ->
-               (* we don't handle cases where t2 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t2 g s
+        in if b1 then eval t2 g s'
+        else eval t3 g s'
+    | Makepair (t1, t2) ->
+        let (value1, s') = eval t1 g s
+        in let (value2, s'') = eval t2 g s'
+        in (Pair (value1, value2), s'')
+    | First (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Pair *)
+        let (Pair (value1, value2), s') = eval t1 g s
+        in (value1, s')
+    | Lambda (arg_var, t2) -> (Closure (arg_var, t2, g), s)
+    | Apply (t1, t2) ->
+        (* we don't handle cases where t1 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t1 g s
+        in let (value2, s'') = eval t2 g s'
+        (* evaluate body under savedg, except with arg_var bound to Nonrecursive value2 *)
+        in let savedg' = (arg_var, Nonrecursive value2) :: savedg
+        in eval body savedg' s''
+    | Letrec (var_to_bind, t2, t3) ->
+        (* we don't handle cases where t2 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t2 g s

         (* evaluate t3 under a new assignment where var_to_bind has been recursively bound to that function value *) 
         (* evaluate t3 under a new assignment where var_to_bind has been recursively bound to that function value *) 

-               in let g' = (var_to_bind, Recursive_Closure (var_to_bind, arg_var, body, savedg)) :: g
-               in eval t3 g' s'
-       | Newref (t1) ->
-               let (starting_val, s') = eval t1 g s
-               (* note that s' may be different from s, if t1 itself contained any mutation operations *)
-               (* now we want to retrieve the next free index in s' *)
-               in let new_index = List.length s'
-               (* now we want to insert starting_val there; the following is an easy but inefficient way to do it *)
-               in let s'' = List.append s' [starting_val]
-               (* now we return a pair of a wrapped new_index, and the new store *)
-               in (Mutcell new_index, s'')
-       | Deref (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Mutcell *)
-               let (Mutcell index1, s') = eval t1 g s
-               (* note that s' may be different from s, if t1 itself contained any mutation operations *)
-               in (List.nth s' index1, s')
-       | Setref (t1, t2) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Mutcell *)
-               let (Mutcell index1, s') = eval t1 g s
-               (* note that s' may be different from s, if t1 itself contained any mutation operations *)
-               in let (new_value, s'') = eval t2 g s'
-               (* now we create a list which is just like s'' except it has new_value in index1 *)
-               in let rec replace_nth lst m =
-                       match lst with
-                       | [] -> failwith "list too short"
-                       | x::xs when m = 0 -> new_value :: xs
-                       | x::xs -> x :: replace_nth xs (m - 1)
-               in let s''' = replace_nth s'' index1
-               (* we'll arbitrarily return Int 42 as the expressed_value of a Setref operation *)
-               in (Int 42, s''')
+        in let g' = (var_to_bind, Recursive_Closure (var_to_bind, arg_var, body, savedg)) :: g
+        in eval t3 g' s'
+    | Newref (t1) ->
+        let (starting_val, s') = eval t1 g s
+        (* note that s' may be different from s, if t1 itself contained any mutation operations *)
+        (* now we want to retrieve the next free index in s' *)
+        in let new_index = List.length s'
+        (* now we want to insert starting_val there; the following is an easy but inefficient way to do it *)
+        in let s'' = List.append s' [starting_val]
+        (* now we return a pair of a wrapped new_index, and the new store *)
+        in (Mutcell new_index, s'')
+    | Deref (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Mutcell *)
+        let (Mutcell index1, s') = eval t1 g s
+        (* note that s' may be different from s, if t1 itself contained any mutation operations *)
+        in (List.nth s' index1, s')
+    | Setref (t1, t2) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Mutcell *)
+        let (Mutcell index1, s') = eval t1 g s
+        (* note that s' may be different from s, if t1 itself contained any mutation operations *)
+        in let (new_value, s'') = eval t2 g s'
+        (* now we create a list which is just like s'' except it has new_value in index1 *)
+        in let rec replace_nth lst m =
+            match lst with
+            | [] -> failwith "list too short"
+            | x::xs when m = 0 -> new_value :: xs
+            | x::xs -> x :: replace_nth xs (m - 1)
+        in let s''' = replace_nth s'' index1
+        (* we'll arbitrarily return Int 42 as the expressed_value of a Setref operation *)
+        in (Int 42, s''')

     ;;
     ;;

diff --git a/code/calculator/calc5.ml b/code/calculator/calc5.ml
index bfc91d9..16e9200 100644 (file)
--- a/code/calculator/calc5.ml
+++ b/code/calculator/calc5.ml
@@ -1,6 +1,6 @@
 (* calc3,ml, enhanced with Mutable Pairs *)
 
 (* calc3,ml, enhanced with Mutable Pairs *)
 

-       type term =
+    type term =

       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)
       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)


@@ -16,80 +16,80 @@
     | Setfirst of (term * term)
     ;;
 
     | Setfirst of (term * term)
     ;;
 

-       type index = int;;
+    type index = int;;

 
     type bound_value = Nonrecursive of expressed_value | Recursive_Closure of char * char * term * assignment
 
     type bound_value = Nonrecursive of expressed_value | Recursive_Closure of char * char * term * assignment

-       and assignment = (char * bound_value) list
+    and assignment = (char * bound_value) list

     and expressed_value = Int of int | Bool of bool | Pair of index * index | Closure of char * term * assignment;;
 
     and expressed_value = Int of int | Bool of bool | Pair of index * index | Closure of char * term * assignment;;
 

-       type store = expressed_value list;;
+    type store = expressed_value list;;

 
 

-       let rec eval (t : term) (g : assignment) (s : store) = match t with
-         Intconstant x -> (Int x, s)
-       | Multiplication (t1, t2) ->
-               (* we don't handle cases where the subterms don't evaluate to Ints *)
-               let (Int i1, s') = eval t1 g s
-               in let (Int i2, s'') = eval t2 g s'
-               (* Multiplication (t1, t2) should evaluate to an Int *)
-               in (Int (i1 * i2), s'')
-       | Addition (t1, t2) ->
-               let (Int i1, s') = eval t1 g s
-               in let (Int i2, s'') = eval t2 g s'
-               in (Int (i1 + i2), s'')
-       | Variable (var) -> (
-               (* we don't handle cases where g doesn't bind var to any value *)
-               match List.assoc var g with
+    let rec eval (t : term) (g : assignment) (s : store) = match t with
+      Intconstant x -> (Int x, s)
+    | Multiplication (t1, t2) ->
+        (* we don't handle cases where the subterms don't evaluate to Ints *)
+        let (Int i1, s') = eval t1 g s
+        in let (Int i2, s'') = eval t2 g s'
+        (* Multiplication (t1, t2) should evaluate to an Int *)
+        in (Int (i1 * i2), s'')
+    | Addition (t1, t2) ->
+        let (Int i1, s') = eval t1 g s
+        in let (Int i2, s'') = eval t2 g s'
+        in (Int (i1 + i2), s'')
+    | Variable (var) -> (
+        (* we don't handle cases where g doesn't bind var to any value *)
+        match List.assoc var g with

           | Nonrecursive value -> value
           | Recursive_Closure (self_var, arg_var, body, savedg) as rec_closure ->
           | Nonrecursive value -> value
           | Recursive_Closure (self_var, arg_var, body, savedg) as rec_closure ->

-                         (* we update savedg to bind self_var to rec_closure here *)
+              (* we update savedg to bind self_var to rec_closure here *)

               let savedg' = (self_var, rec_closure) :: savedg
               in Closure (arg_var, body, savedg')
         ), s
               let savedg' = (self_var, rec_closure) :: savedg
               in Closure (arg_var, body, savedg')
         ), s

-       | Let (var_to_bind, t2, t3) ->
-               (* evaluate t3 under a new assignment where var_to_bind has been bound to
+    | Let (var_to_bind, t2, t3) ->
+        (* evaluate t3 under a new assignment where var_to_bind has been bound to

            the result of evaluating t2 under the current assignment *)
            the result of evaluating t2 under the current assignment *)

-               let (value2, s') = eval t2 g s
-               (* we have to wrap value2 in Nonrecursive *)
-               in let g' = (var_to_bind, Nonrecursive value2) :: g
-               in eval t3 g' s'
-       | Iszero (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to an Int *)
-               let (Int i1, s') = eval t1 g s
-               (* Iszero t1 should evaluate to a Bool *)
-               in (Bool (i1 = 0), s')
-       | If (t1, t2, t3) ->
-               (* we don't handle cases where t1 doesn't evaluate to a boolean *)
-               let (Bool b1, s') = eval t1 g s
+        let (value2, s') = eval t2 g s
+        (* we have to wrap value2 in Nonrecursive *)
+        in let g' = (var_to_bind, Nonrecursive value2) :: g
+        in eval t3 g' s'
+    | Iszero (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to an Int *)
+        let (Int i1, s') = eval t1 g s
+        (* Iszero t1 should evaluate to a Bool *)
+        in (Bool (i1 = 0), s')
+    | If (t1, t2, t3) ->
+        (* we don't handle cases where t1 doesn't evaluate to a boolean *)
+        let (Bool b1, s') = eval t1 g s

         (* note we thread s' through only one of the then/else clauses *)
         (* note we thread s' through only one of the then/else clauses *)

-               in if b1 then eval t2 g s'
-               else eval t3 g s'
-       | Makepair (t1, t2) ->
-               let (value1, s') = eval t1 g s
-               in let (value2, s'') = eval t2 g s'
+        in if b1 then eval t2 g s'
+        else eval t3 g s'
+    | Makepair (t1, t2) ->
+        let (value1, s') = eval t1 g s
+        in let (value2, s'') = eval t2 g s'

         (* now we want to retrieve the next free index in s'' *)
         in let new_index = List.length s''
         (* now we want to insert value1 and value2 there; the following is an easy but inefficient way to do it *)
         in let s''' = List.append s'' [value1; value2]
         (* now we want to retrieve the next free index in s'' *)
         in let new_index = List.length s''
         (* now we want to insert value1 and value2 there; the following is an easy but inefficient way to do it *)
         in let s''' = List.append s'' [value1; value2]

-               in (Pair (new_index, new_index + 1), s''')
-       | First (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Pair *)
-               let (Pair (index1, index2), s') = eval t1 g s
+        in (Pair (new_index, new_index + 1), s''')
+    | First (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Pair *)
+        let (Pair (index1, index2), s') = eval t1 g s

         (* note that s' may be different from s, if t1 itself contained any mutation operations *)
         in (List.nth s' index1, s')
         (* note that s' may be different from s, if t1 itself contained any mutation operations *)
         in (List.nth s' index1, s')

-       | Lambda (arg_var, t2) -> (Closure (arg_var, t2, g), s)
-       | Apply (t1, t2) ->
-               (* we don't handle cases where t1 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t1 g s
-               in let (value2, s'') = eval t2 g s'
-               (* evaluate body under savedg, except with arg_var bound to Nonrecursive value2 *)
-               in let savedg' = (arg_var, Nonrecursive value2) :: savedg
-               in eval body savedg' s''
-       | Letrec (var_to_bind, t2, t3) ->
-               (* we don't handle cases where t2 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t2 g s
+    | Lambda (arg_var, t2) -> (Closure (arg_var, t2, g), s)
+    | Apply (t1, t2) ->
+        (* we don't handle cases where t1 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t1 g s
+        in let (value2, s'') = eval t2 g s'
+        (* evaluate body under savedg, except with arg_var bound to Nonrecursive value2 *)
+        in let savedg' = (arg_var, Nonrecursive value2) :: savedg
+        in eval body savedg' s''
+    | Letrec (var_to_bind, t2, t3) ->
+        (* we don't handle cases where t2 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t2 g s

         (* evaluate t3 under a new assignment where var_to_bind has been recursively bound to that function value *) 
         (* evaluate t3 under a new assignment where var_to_bind has been recursively bound to that function value *) 

-               in let g' = (var_to_bind, Recursive_Closure (var_to_bind, arg_var, body, savedg)) :: g
-               in eval t3 g' s'
+        in let g' = (var_to_bind, Recursive_Closure (var_to_bind, arg_var, body, savedg)) :: g
+        in eval t3 g' s'

     | Setfirst (t1, t2) ->
         (* we don't handle cases where t1 doesn't evaluate to a Pair *)
         let (Pair (index1, index2), s') = eval t1 g s
     | Setfirst (t1, t2) ->
         (* we don't handle cases where t1 doesn't evaluate to a Pair *)
         let (Pair (index1, index2), s') = eval t1 g s

diff --git a/code/calculator/calc6.ml b/code/calculator/calc6.ml
index 381e543..fa3f183 100644 (file)
--- a/code/calculator/calc6.ml
+++ b/code/calculator/calc6.ml
@@ -1,6 +1,6 @@
 (* calc3.ml, enhanced with Mutable Variables *)
 
 (* calc3.ml, enhanced with Mutable Variables *)
 

-       type term =
+    type term =

       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)
       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)


@@ -16,91 +16,91 @@
     | Change of (char * term * term)
     ;;
 
     | Change of (char * term * term)
     ;;
 

-       type index = int;;
+    type index = int;;

 
     type bound_value = index;;
     type assignment = (char * bound_value) list;;
 
     type bound_value = index;;
     type assignment = (char * bound_value) list;;

-       type expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment;;
+    type expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment;;

 
 

-       type store = expressed_value list;;
+    type store = expressed_value list;;

 
 

-       let rec eval (t : term) (g : assignment) (s : store) = match t with
-         Intconstant x -> (Int x, s)
-       | Multiplication (t1, t2) ->
-               (* we don't handle cases where the subterms don't evaluate to Ints *)
-               let (Int i1, s') = eval t1 g s
-               in let (Int i2, s'') = eval t2 g s'
-               (* Multiplication (t1, t2) should evaluate to an Int *)
-               in (Int (i1 * i2), s'')
-       | Addition (t1, t2) ->
-               let (Int i1, s') = eval t1 g s
-               in let (Int i2, s'') = eval t2 g s'
-               in (Int (i1 + i2), s'')
-       | Variable (var) ->
-               (* we don't handle cases where g doesn't bind var to any value *)
+    let rec eval (t : term) (g : assignment) (s : store) = match t with
+      Intconstant x -> (Int x, s)
+    | Multiplication (t1, t2) ->
+        (* we don't handle cases where the subterms don't evaluate to Ints *)
+        let (Int i1, s') = eval t1 g s
+        in let (Int i2, s'') = eval t2 g s'
+        (* Multiplication (t1, t2) should evaluate to an Int *)
+        in (Int (i1 * i2), s'')
+    | Addition (t1, t2) ->
+        let (Int i1, s') = eval t1 g s
+        in let (Int i2, s'') = eval t2 g s'
+        in (Int (i1 + i2), s'')
+    | Variable (var) ->
+        (* we don't handle cases where g doesn't bind var to any value *)

         let index = List.assoc var g
         (* get value stored at location index in s *)
         in let value = List.nth s index
         in (value, s)
         let index = List.assoc var g
         (* get value stored at location index in s *)
         in let value = List.nth s index
         in (value, s)

-       | Let (var_to_bind, t2, t3) ->
-               let (value2, s') = eval t2 g s
-               (* note that s' may be different from s, if t2 itself contained any mutation operations *)
+    | Let (var_to_bind, t2, t3) ->
+        let (value2, s') = eval t2 g s
+        (* note that s' may be different from s, if t2 itself contained any mutation operations *)

         (* get next free index in s' *)
         (* get next free index in s' *)

-               in let new_index = List.length s'
-               (* now we want to insert value2 there; the following is an easy but inefficient way to do it *)
-               in let s'' = List.append s' [value2]
+        in let new_index = List.length s'
+        (* now we want to insert value2 there; the following is an easy but inefficient way to do it *)
+        in let s'' = List.append s' [value2]

         (* bind var_to_bind to location new_index in the store *)
         in let g' = ((var_to_bind, new_index) :: g)
         in eval t3 g' s''
         (* bind var_to_bind to location new_index in the store *)
         in let g' = ((var_to_bind, new_index) :: g)
         in eval t3 g' s''

-       | Iszero (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to an Int *)
-               let (Int i1, s') = eval t1 g s
-               (* Iszero t1 should evaluate to a Bool *)
-               in (Bool (i1 = 0), s')
-       | If (t1, t2, t3) ->
-               (* we don't handle cases where t1 doesn't evaluate to a boolean *)
-               let (Bool b1, s') = eval t1 g s
+    | Iszero (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to an Int *)
+        let (Int i1, s') = eval t1 g s
+        (* Iszero t1 should evaluate to a Bool *)
+        in (Bool (i1 = 0), s')
+    | If (t1, t2, t3) ->
+        (* we don't handle cases where t1 doesn't evaluate to a boolean *)
+        let (Bool b1, s') = eval t1 g s

         (* note we thread s' through only one of the then/else clauses *)
         (* note we thread s' through only one of the then/else clauses *)

-               in if b1 then eval t2 g s'
-               else eval t3 g s'
-       | Makepair (t1, t2) ->
-               let (value1, s') = eval t1 g s
-               in let (value2, s'') = eval t2 g s'
-               in (Pair (value1, value2), s'')
-       | First (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Pair *)
-               let (Pair (value1, value2), s') = eval t1 g s
-               in (value1, s')
-       | Lambda (arg_var, t2) -> (Closure (arg_var, t2, g), s)
-       | Apply (t1, t2) ->
-               (* we don't handle cases where t1 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t1 g s
-               in let (value2, s'') = eval t2 g s'
-               (* evaluate body under savedg, except with arg_var bound to a new location containing value2 *)
+        in if b1 then eval t2 g s'
+        else eval t3 g s'
+    | Makepair (t1, t2) ->
+        let (value1, s') = eval t1 g s
+        in let (value2, s'') = eval t2 g s'
+        in (Pair (value1, value2), s'')
+    | First (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Pair *)
+        let (Pair (value1, value2), s') = eval t1 g s
+        in (value1, s')
+    | Lambda (arg_var, t2) -> (Closure (arg_var, t2, g), s)
+    | Apply (t1, t2) ->
+        (* we don't handle cases where t1 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t1 g s
+        in let (value2, s'') = eval t2 g s'
+        (* evaluate body under savedg, except with arg_var bound to a new location containing value2 *)

         in let new_index = List.length s''
         in let s''' = List.append s'' [value2]
         in let new_index = List.length s''
         in let s''' = List.append s'' [value2]

-               in let savedg' = (arg_var, new_index) :: savedg
-               in eval body savedg' s'''
-       | Letrec (var_to_bind, t2, t3) ->
-               (* we don't handle cases where t2 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t2 g s
+        in let savedg' = (arg_var, new_index) :: savedg
+        in eval body savedg' s'''
+    | Letrec (var_to_bind, t2, t3) ->
+        (* we don't handle cases where t2 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t2 g s

         in let new_index = List.length s'
         in let savedg' = (var_to_bind, new_index) :: savedg
         in let new_closure = Closure (arg_var, body, savedg')
         in let s'' = List.append s' [new_closure]
         in let g' = (var_to_bind, new_index) :: g
         in eval t3 g' s''
         in let new_index = List.length s'
         in let savedg' = (var_to_bind, new_index) :: savedg
         in let new_closure = Closure (arg_var, body, savedg')
         in let s'' = List.append s' [new_closure]
         in let g' = (var_to_bind, new_index) :: g
         in eval t3 g' s''

-       | Change (var, t2, t3) ->
-               (* we don't handle cases where g doesn't bind var to any value *)
+    | Change (var, t2, t3) ->
+        (* we don't handle cases where g doesn't bind var to any value *)

         let index = List.assoc var g
         in let (value2, s') = eval t2 g s
         let index = List.assoc var g
         in let (value2, s') = eval t2 g s

-               (* note that s' may be different from s, if t2 itself contained any mutation operations *)
-               (* now we create a list which is just like s' except it has value2 at index *)
-               in let rec replace_nth lst m =
-                       match lst with
-                       | [] -> failwith "list too short"
-                       | x::xs when m = 0 -> value2 :: xs
-                       | x::xs -> x :: replace_nth xs (m - 1)
+        (* note that s' may be different from s, if t2 itself contained any mutation operations *)
+        (* now we create a list which is just like s' except it has value2 at index *)
+        in let rec replace_nth lst m =
+            match lst with
+            | [] -> failwith "list too short"
+            | x::xs when m = 0 -> value2 :: xs
+            | x::xs -> x :: replace_nth xs (m - 1)

         in let s'' = replace_nth s' index
         (* evaluate t3 using original assignment function and new store *)
         in eval t3 g s''
         in let s'' = replace_nth s' index
         (* evaluate t3 using original assignment function and new store *)
         in eval t3 g s''

diff --git a/code/calculator/calc7.ml b/code/calculator/calc7.ml
index 5bfba38..6fc6338 100644 (file)
--- a/code/calculator/calc7.ml
+++ b/code/calculator/calc7.ml
@@ -1,6 +1,6 @@
 (* calc6.ml, enhanced with Aliases and Passing by Reference *)
 
 (* calc6.ml, enhanced with Aliases and Passing by Reference *)
 

-       type term =
+    type term =

       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)
       Intconstant of int
     | Multiplication of (term * term)
     | Addition of (term * term)


@@ -18,107 +18,107 @@
     | Applyalias of (term * char)
     ;;
 
     | Applyalias of (term * char)
     ;;
 

-       type index = int;;
+    type index = int;;

 
     type bound_value = index;;
     type assignment = (char * bound_value) list;;
 
     type bound_value = index;;
     type assignment = (char * bound_value) list;;

-       type expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment;;
+    type expressed_value = Int of int | Bool of bool | Pair of expressed_value * expressed_value | Closure of char * term * assignment;;

 
 

-       type store = expressed_value list;;
+    type store = expressed_value list;;

 
 

-       let rec eval (t : term) (g : assignment) (s : store) = match t with
-         Intconstant x -> (Int x, s)
-       | Multiplication (t1, t2) ->
-               (* we don't handle cases where the subterms don't evaluate to Ints *)
-               let (Int i1, s') = eval t1 g s
-               in let (Int i2, s'') = eval t2 g s'
-               (* Multiplication (t1, t2) should evaluate to an Int *)
-               in (Int (i1 * i2), s'')
-       | Addition (t1, t2) ->
-               let (Int i1, s') = eval t1 g s
-               in let (Int i2, s'') = eval t2 g s'
-               in (Int (i1 + i2), s'')
-       | Variable (var) ->
-               (* we don't handle cases where g doesn't bind var to any value *)
+    let rec eval (t : term) (g : assignment) (s : store) = match t with
+      Intconstant x -> (Int x, s)
+    | Multiplication (t1, t2) ->
+        (* we don't handle cases where the subterms don't evaluate to Ints *)
+        let (Int i1, s') = eval t1 g s
+        in let (Int i2, s'') = eval t2 g s'
+        (* Multiplication (t1, t2) should evaluate to an Int *)
+        in (Int (i1 * i2), s'')
+    | Addition (t1, t2) ->
+        let (Int i1, s') = eval t1 g s
+        in let (Int i2, s'') = eval t2 g s'
+        in (Int (i1 + i2), s'')
+    | Variable (var) ->
+        (* we don't handle cases where g doesn't bind var to any value *)

         let index = List.assoc var g
         (* get value stored at location index in s *)
         in let value = List.nth s index
         in (value, s)
         let index = List.assoc var g
         (* get value stored at location index in s *)
         in let value = List.nth s index
         in (value, s)

-       | Let (var_to_bind, t2, t3) ->
-               let (value2, s') = eval t2 g s
-               (* note that s' may be different from s, if t2 itself contained any mutation operations *)
+    | Let (var_to_bind, t2, t3) ->
+        let (value2, s') = eval t2 g s
+        (* note that s' may be different from s, if t2 itself contained any mutation operations *)

         (* get next free index in s' *)
         (* get next free index in s' *)

-               in let new_index = List.length s'
-               (* now we want to insert value2 there; the following is an easy but inefficient way to do it *)
-               in let s'' = List.append s' [value2]
+        in let new_index = List.length s'
+        (* now we want to insert value2 there; the following is an easy but inefficient way to do it *)
+        in let s'' = List.append s' [value2]

         (* bind var_to_bind to location new_index in the store *)
         in let g' = ((var_to_bind, new_index) :: g)
         in eval t3 g' s''
         (* bind var_to_bind to location new_index in the store *)
         in let g' = ((var_to_bind, new_index) :: g)
         in eval t3 g' s''

-       | Iszero (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to an Int *)
-               let (Int i1, s') = eval t1 g s
-               (* Iszero t1 should evaluate to a Bool *)
-               in (Bool (i1 = 0), s')
-       | If (t1, t2, t3) ->
-               (* we don't handle cases where t1 doesn't evaluate to a boolean *)
-               let (Bool b1, s') = eval t1 g s
+    | Iszero (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to an Int *)
+        let (Int i1, s') = eval t1 g s
+        (* Iszero t1 should evaluate to a Bool *)
+        in (Bool (i1 = 0), s')
+    | If (t1, t2, t3) ->
+        (* we don't handle cases where t1 doesn't evaluate to a boolean *)
+        let (Bool b1, s') = eval t1 g s

         (* note we thread s' through only one of the then/else clauses *)
         (* note we thread s' through only one of the then/else clauses *)

-               in if b1 then eval t2 g s'
-               else eval t3 g s'
-       | Makepair (t1, t2) ->
-               let (value1, s') = eval t1 g s
-               in let (value2, s'') = eval t2 g s'
-               in (Pair (value1, value2), s'')
-       | First (t1) ->
-               (* we don't handle cases where t1 doesn't evaluate to a Pair *)
-               let (Pair (value1, value2), s') = eval t1 g s
-               in (value1, s')
-       | Lambda (arg_var, t2) -> (Closure (arg_var, t2, g), s)
-       | Apply (t1, t2) ->
-               (* we don't handle cases where t1 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t1 g s
-               in let (value2, s'') = eval t2 g s'
-               (* evaluate body under savedg, except with arg_var bound to a new location containing value2 *)
+        in if b1 then eval t2 g s'
+        else eval t3 g s'
+    | Makepair (t1, t2) ->
+        let (value1, s') = eval t1 g s
+        in let (value2, s'') = eval t2 g s'
+        in (Pair (value1, value2), s'')
+    | First (t1) ->
+        (* we don't handle cases where t1 doesn't evaluate to a Pair *)
+        let (Pair (value1, value2), s') = eval t1 g s
+        in (value1, s')
+    | Lambda (arg_var, t2) -> (Closure (arg_var, t2, g), s)
+    | Apply (t1, t2) ->
+        (* we don't handle cases where t1 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t1 g s
+        in let (value2, s'') = eval t2 g s'
+        (* evaluate body under savedg, except with arg_var bound to a new location containing value2 *)

         in let new_index = List.length s''
         in let s''' = List.append s'' [value2]
         in let new_index = List.length s''
         in let s''' = List.append s'' [value2]

-               in let savedg' = (arg_var, new_index) :: savedg
-               in eval body savedg' s'''
-       | Letrec (var_to_bind, t2, t3) ->
-               (* we don't handle cases where t2 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t2 g s
+        in let savedg' = (arg_var, new_index) :: savedg
+        in eval body savedg' s'''
+    | Letrec (var_to_bind, t2, t3) ->
+        (* we don't handle cases where t2 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t2 g s

         in let new_index = List.length s'
         in let savedg' = (var_to_bind, new_index) :: savedg
         in let new_closure = Closure (arg_var, body, savedg')
         in let s'' = List.append s' [new_closure]
         in let g' = (var_to_bind, new_index) :: g
         in eval t3 g' s''
         in let new_index = List.length s'
         in let savedg' = (var_to_bind, new_index) :: savedg
         in let new_closure = Closure (arg_var, body, savedg')
         in let s'' = List.append s' [new_closure]
         in let g' = (var_to_bind, new_index) :: g
         in eval t3 g' s''

-       | Change (var, t2, t3) ->
-               (* we don't handle cases where g doesn't bind var to any value *)
+    | Change (var, t2, t3) ->
+        (* we don't handle cases where g doesn't bind var to any value *)

         let index = List.assoc var g
         in let (value2, s') = eval t2 g s
         let index = List.assoc var g
         in let (value2, s') = eval t2 g s

-               (* note that s' may be different from s, if t2 itself contained any mutation operations *)
-               (* now we create a list which is just like s' except it has value2 at index *)
-               in let rec replace_nth lst m =
-                       match lst with
-                       | [] -> failwith "list too short"
-                       | x::xs when m = 0 -> value2 :: xs
-                       | x::xs -> x :: replace_nth xs (m - 1)
+        (* note that s' may be different from s, if t2 itself contained any mutation operations *)
+        (* now we create a list which is just like s' except it has value2 at index *)
+        in let rec replace_nth lst m =
+            match lst with
+            | [] -> failwith "list too short"
+            | x::xs when m = 0 -> value2 :: xs
+            | x::xs -> x :: replace_nth xs (m - 1)

         in let s'' = replace_nth s' index
         (* evaluate t3 using original assignment function and new store *)
         in eval t3 g s''
         in let s'' = replace_nth s' index
         (* evaluate t3 using original assignment function and new store *)
         in eval t3 g s''

-       | Alias (var_to_bind, orig_var, t3) ->
-               (* we don't handle cases where g doesn't bind orig_var to any value *)
+    | Alias (var_to_bind, orig_var, t3) ->
+        (* we don't handle cases where g doesn't bind orig_var to any value *)

         let index = List.assoc orig_var g
         (* bind var_to_bind to the same index in the store *)
         in let g' = ((var_to_bind, index) :: g)
         in eval t3 g' s
         let index = List.assoc orig_var g
         (* bind var_to_bind to the same index in the store *)
         in let g' = ((var_to_bind, index) :: g)
         in eval t3 g' s

-       | Applyalias (t1, var) ->
-               (* we don't handle cases where t1 doesn't evaluate to a function value *)
-               let (Closure (arg_var, body, savedg), s') = eval t1 g s
-               (* we don't handle cases where g doesn't bind var to any value *)
+    | Applyalias (t1, var) ->
+        (* we don't handle cases where t1 doesn't evaluate to a function value *)
+        let (Closure (arg_var, body, savedg), s') = eval t1 g s
+        (* we don't handle cases where g doesn't bind var to any value *)

         in let index = List.assoc var g
         in let index = List.assoc var g

-               (* evaluate body under savedg, except with arg_var bound to existing index *)
-               in let savedg' = (arg_var, index) :: savedg
-               in eval body savedg' s'
+        (* evaluate body under savedg, except with arg_var bound to existing index *)
+        in let savedg' = (arg_var, index) :: savedg
+        in eval body savedg' s'

     ;;
 
     ;;