- 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