+++ /dev/null
-(* calc1.ml: original calculator from Week7, enhanced with Booleans and Immutable Pairs *)
-
- type term =
- Intconstant of int
- | Multiplication of (term * term)
- | Addition of (term * term)
- | Variable of char
- | Let of (char * term * term)
- | Iszero of term
- | If of (term * term * term)
- | Makepair of (term * 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;;
-
- 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
- ;;