let makeStream this state next $=$

$(($this$,$ state$),$ next$)$ ;;

$(*$ FIRST. Return the first element of a stream. $*)$

let first $(($this$,$ state$),$ next$)=$

this ;;

$(*$ REST. Return a stream with its first element removed. $*)$

let rest $(($this$,$ state$),$ next$)=$

$($next this state, next$)$ ;;

$(*$ TAKE. Return a list of the first COUNT elements TAKEn from STREAM. $*)$

let rec take count stream $=$

match count

with $0->[]|$

$\_->($first stream$)$ :: take $($count $-1)($rest stream$)$ ;;

$(*$ NATURALS. A infinite stream of $0,1,2,3,4,5,6,7,8,9...$ We don't use

STATE here, so we let it be the dummy unit object $().*)$

let naturals $=$

makeStream $0()($fun this state $->($this $+1,()))$ ;;

let odds $=$

let rec generate$\_$odd n $=$ makeStream n $($n $+2)($fun this state $->($this $+$ state, state $+2))$ in

generate$\_$odd $1$ ;;

let rec trim count stream $=$

match count with

$|0->$ stream

$|\_->$ trim $($count $-1)($rest stream$)$ ;;

let rec scale factor stream $=$

let newThis $=$ first stream $*$ factor in

let newState $=($factor$,$ rest stream$)$ in

makeStream newThis newState $($fun $(\_,$ restState$)->$ scale factor restState$)$

let rec sum left right $=$

let combine $($stream$1,$ stream$2)=($first stream$1+$ first stream$2,($rest stream$1,$ rest stream$2))$ in

makeStream $($combine $($left$,$ right$))($combine$)($fun $\_\_->$ sum $($rest left$)($rest right$))$ ;;

My error is a type mismatch error at:

let rec scale factor stream $=$

let newThis $=$ first stream $*$ factor in

let newState $=($factor$,$ rest stream$)$ in

makeStream newThis newState $($fun $(\_,$ restState$)->$ scale factor restState$)$

$55$

makeStream newThis newState $($fun $($

expression has type$($int $*($int $*(\text{'}$a $*($int $->\text{'}$b $->\text{'}$a$))))*(\text{'}$c $*(($int $*\text{'}$b$)*($int $->>\text{'}$b $->>\text{'}$a$))->$d$)$

but an expression was expected of type $\text{'}$d

The type variable $\text{'}$d occurs inside

$($int $*($int $*(\text{'}$a $*($int $->\text{'}$b $->\text{'}$a$))))*(\text{'}$c $*(($int $*\text{'}$b$)*($int $->>\text{'}$b $->>\text{'}$a$))->$d$)$