F# Active Pattern List.filter or equivalent
- by akaphenom
I have a records of types
type tradeLeg = {
id : int ;
tradeId : int ;
legActivity : LegActivityType ;
actedOn : DateTime ;
estimates : legComponents ;
entryType : ShareOrDollarBased ;
confirmedPrice: DollarsPerShare option;
actuals : legComponents option ;
type trade = {
id : int ;
securityId : int ;
ricCode : string ;
tradeActivity : TradeType ;
enteredOn : DateTime ;
closedOn : DateTime ;
tradeLegs : tradeLeg list ;
}
Obviously the tradeLegs are a type off of a trade. A leg may be settled or unsettled (or unsettled but price confirmed) - thus I have defined the active pattern:
let (|LegIsSettled|LegIsConfirmed|LegIsUnsettled|) (l: tradeLeg) =
if Helper.exists l.actuals then LegIsSettled
elif Helper.exists l.confirmedPrice then LegIsConfirmed
else LegIsUnsettled
and then to determine if a trade is settled (based on all legs matching LegIsSettled pattern:
let (|TradeIsSettled|TradeIsUnsettled|) (t: trade) =
if List.exists (
fun l ->
match l with
| LegIsSettled -> false
| _ -> true) t.tradeLegs then TradeIsSettled
else TradeIsUnsettled
I can see some advantages of this use of active patterns, however i would think there is a more efficient way to see if any item of a list either matches (or doesn't) an actie pattern without having to write a lambda expression specifically for it, and using List.exist.
Question is two fold:
is there a more concise way to express this?
is there a way to abstract the functionality / expression
(fun l -
match l with
| LegIsSettled - false
| _ - true)
Such that
let itemMatchesPattern pattern item =
match item with
| pattern -> true
| _ -> false
such I could write (as I am reusing this design-pattern):
let curriedItemMatchesPattern = itemMatchesPattern LegIsSettled
if List.exists curriedItemMatchesPattern t.tradeLegs then TradeIsSettled
else TradeIsUnsettled
Thoughts?
