Re: [racket-users] how to use union types
. . . all of which suggests that perhaps we should support blazingly fast list chaperones eventually :) -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
On 2/28/19, Brian Craft wrote: > So, when working with large data that is internal to an app, where schema > is guaranteed by serialization, there's no way to load that without another > O(N) pass to satisfy the type checker? Right. This is how the type checker helps find & prevent bugs. There's no way to safely turn a JSExpr into a (Listof String) without proving that the data really is a list that really contains Strings and nothing else. If you know more about the schema and this O(N) pass is too slow, then you may want to write a function that parses a list from an input port and simultaneously checks the type of its elements. That will save 1 traversal. You can also delay the validation by writing functions that accept JSExpr data and perform pair? and string? checks as needed. This may or may not save time overall --- it depends on the program. Anything else is unsafe. (Wrapping in a struct helps if the (Listof String) needs to visit typed and untyped code.) -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
There is, but it's called "wrap your data in a struct". The type checker doesn't know that serialization guarantees your schema, and you haven't proved that *only* previously-serialized data will be constructed. In order to represent this knowledge with types, you can create a struct wrapper in a module that exports functions that guarantee the property is checked exactly once, when the struct is constructed. This doesn't remove the O(N) pass, but it does prevent you from having *multiple* O(N) passes as you hand off data between functions. With the struct wrapper, constructing instances requires the O(N) check but passing instances between functions that accept the struct type is a constant-time struct predicate test. On Thursday, February 28, 2019 at 2:43:32 PM UTC-8, Brian Craft wrote: > > So, when working with large data that is internal to an app, where schema > is guaranteed by serialization, there's no way to load that without another > O(N) pass to satisfy the type checker? > > > On Thursday, February 28, 2019 at 1:03:48 PM UTC-8, Sam Tobin-Hochstadt > wrote: >> >> Yes, a cast to a List type checks all the elements of the list. >> There's no way to tell if every element of list is a string in less >> than O(N) time -- that information just isn't available anywhere. >> >> Sam >> >> On Thu, Feb 28, 2019 at 3:52 PM Brian Craft wrote: >> > >> > Really? A cast is also O(N)? >> > >> > On Thursday, February 28, 2019 at 11:11:01 AM UTC-8, Sam >> Tobin-Hochstadt wrote: >> >> >> >> Any of these solutions need a O(N) traversal of the data. That's >> >> because we need to do a full traversal to be sure we got an actual >> >> (Listof String) from read-json -- there's no way around it. >> >> >> >> Sam >> >> >> >> On Thu, Feb 28, 2019 at 2:04 PM Brian Craft >> wrote: >> >> > >> >> > I would think there'd be a large performance issue, as well, due to >> needing an O(N) walk of the data. I'm having type checker issues with >> (time), so haven't tested it, but maybe (cast) will get me past those. >> >> > >> >> > Thanks! >> >> > >> >> > On Monday, February 25, 2019 at 4:26:52 PM UTC-8, Philip McGrath >> wrote: >> >> >> >> >> >> An alternative to figuring out how to satisfy the type checker is >> to use `cast`, e.g.: >> >> >> #lang typed/racket >> >> >> (require typed/json) >> >> >> (string-join >> >> >> (cast >> >> >> (string->jsexpr >> >> >>"[\"The\",\"quick\",\"brown\",\"fox\",\"...\"]") >> >> >> (Listof String))) >> >> >> >> >> >> Obviously this has pros and cons, the main pro being that it runs. >> The biggest con, in my view, is that you effectively are dropping into >> untyped world. If you figure out how to satisfy the type checker, you get >> assurance that your code is well-typed, which is presumably what you want >> if your using Typed Racket in the first place. Using `cast` means that you >> are responsible for making sure that expression has the type you say it >> does, without help from Typed Racket, or you will get a runtime error. For >> example, I often forget that `read-json` might return `eof` rather than a >> `JSExpr`. Also, `cast` uses the contract machinery, which can carry >> performance costs. >> >> >> >> >> >> But the fact that it runs is not a small benefit, especially if it >> lets you fill in other parts of your program and come back to remove the >> `cast` later. It also lets you take advantage of Typed Racket to generate >> any complicated runtime checks. >> >> >> >> >> >> -Philip >> >> >> >> >> >> >> >> >> On Mon, Feb 25, 2019 at 6:49 PM wrote: >> >> >>> >> >> >>> A JSExpr is one of a couple of things: >> >> >>> >> >> >>> - A list >> >> >>> - A hash with symbol keys >> >> >>> - A number >> >> >>> - A string >> >> >>> - A boolean >> >> >>> - Null >> >> >>> >> >> >>> The (andmap string?) approach implicitly assumes you're giving it >> a list. But it might be something else instead, so you want this: (and >> (list? js) (andmap string? js)) >> >> >>> >> >> >>> On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft >> wrote: >> >> >> >> So, that also gives me a type error: >> >> >> >> Type Checker: Polymorphic function `andmap' could not be applied >> to arguments: >> >> Domains: (-> a b ... b c) (Listof a) (Listof b) ... b >> >> (-> a c : d) (Listof a) >> >> Arguments: (-> Any Boolean : String) (U EOF JSExpr) >> >> >> >> in: (andmap string? s) >> >> >> >> >> >> On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam >> Tobin-Hochstadt wrote: >> >> > >> >> > I think (andmap string? ...) is probably the easiest way to >> check that. >> >> > >> >> > Sam >> >> > >> >> > On Mon, Feb 25, 2019, 6:20 PM Brian Craft >> wrote: >> >> >> >> >> >> In typed racket, parsing a string list gives me a JSExpr, which >> is a union. I need to pass it to functions that operate on str
Re: [racket-users] how to use union types
So, when working with large data that is internal to an app, where schema is guaranteed by serialization, there's no way to load that without another O(N) pass to satisfy the type checker? On Thursday, February 28, 2019 at 1:03:48 PM UTC-8, Sam Tobin-Hochstadt wrote: > > Yes, a cast to a List type checks all the elements of the list. > There's no way to tell if every element of list is a string in less > than O(N) time -- that information just isn't available anywhere. > > Sam > > On Thu, Feb 28, 2019 at 3:52 PM Brian Craft > wrote: > > > > Really? A cast is also O(N)? > > > > On Thursday, February 28, 2019 at 11:11:01 AM UTC-8, Sam Tobin-Hochstadt > wrote: > >> > >> Any of these solutions need a O(N) traversal of the data. That's > >> because we need to do a full traversal to be sure we got an actual > >> (Listof String) from read-json -- there's no way around it. > >> > >> Sam > >> > >> On Thu, Feb 28, 2019 at 2:04 PM Brian Craft > wrote: > >> > > >> > I would think there'd be a large performance issue, as well, due to > needing an O(N) walk of the data. I'm having type checker issues with > (time), so haven't tested it, but maybe (cast) will get me past those. > >> > > >> > Thanks! > >> > > >> > On Monday, February 25, 2019 at 4:26:52 PM UTC-8, Philip McGrath > wrote: > >> >> > >> >> An alternative to figuring out how to satisfy the type checker is to > use `cast`, e.g.: > >> >> #lang typed/racket > >> >> (require typed/json) > >> >> (string-join > >> >> (cast > >> >> (string->jsexpr > >> >>"[\"The\",\"quick\",\"brown\",\"fox\",\"...\"]") > >> >> (Listof String))) > >> >> > >> >> Obviously this has pros and cons, the main pro being that it runs. > The biggest con, in my view, is that you effectively are dropping into > untyped world. If you figure out how to satisfy the type checker, you get > assurance that your code is well-typed, which is presumably what you want > if your using Typed Racket in the first place. Using `cast` means that you > are responsible for making sure that expression has the type you say it > does, without help from Typed Racket, or you will get a runtime error. For > example, I often forget that `read-json` might return `eof` rather than a > `JSExpr`. Also, `cast` uses the contract machinery, which can carry > performance costs. > >> >> > >> >> But the fact that it runs is not a small benefit, especially if it > lets you fill in other parts of your program and come back to remove the > `cast` later. It also lets you take advantage of Typed Racket to generate > any complicated runtime checks. > >> >> > >> >> -Philip > >> >> > >> >> > >> >> On Mon, Feb 25, 2019 at 6:49 PM wrote: > >> >>> > >> >>> A JSExpr is one of a couple of things: > >> >>> > >> >>> - A list > >> >>> - A hash with symbol keys > >> >>> - A number > >> >>> - A string > >> >>> - A boolean > >> >>> - Null > >> >>> > >> >>> The (andmap string?) approach implicitly assumes you're giving it a > list. But it might be something else instead, so you want this: (and (list? > js) (andmap string? js)) > >> >>> > >> >>> On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft > wrote: > >> > >> So, that also gives me a type error: > >> > >> Type Checker: Polymorphic function `andmap' could not be applied > to arguments: > >> Domains: (-> a b ... b c) (Listof a) (Listof b) ... b > >> (-> a c : d) (Listof a) > >> Arguments: (-> Any Boolean : String) (U EOF JSExpr) > >> > >> in: (andmap string? s) > >> > >> > >> On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam > Tobin-Hochstadt wrote: > >> > > >> > I think (andmap string? ...) is probably the easiest way to check > that. > >> > > >> > Sam > >> > > >> > On Mon, Feb 25, 2019, 6:20 PM Brian Craft > wrote: > >> >> > >> >> In typed racket, parsing a string list gives me a JSExpr, which > is a union. I need to pass it to functions that operate on string lists, > but can't figure out how to please the type checker. Maybe with occurrence > typing? But I don't know how to assert "this is a list of strings". > >> >> > >> >> -- > >> >> You received this message because you are subscribed to the > Google Groups "Racket Users" group. > >> >> To unsubscribe from this group and stop receiving emails from > it, send an email to racket-users...@googlegroups.com. > >> >> For more options, visit https://groups.google.com/d/optout. > >> >>> > >> >>> -- > >> >>> You received this message because you are subscribed to the Google > Groups "Racket Users" group. > >> >>> To unsubscribe from this group and stop receiving emails from it, > send an email to racket-users...@googlegroups.com. > >> >>> For more options, visit https://groups.google.com/d/optout. > >> > > >> > -- > >> > You received this message because you are subscribed to the
Re: [racket-users] how to use union types
Yes, a cast to a List type checks all the elements of the list. There's no way to tell if every element of list is a string in less than O(N) time -- that information just isn't available anywhere. Sam On Thu, Feb 28, 2019 at 3:52 PM Brian Craft wrote: > > Really? A cast is also O(N)? > > On Thursday, February 28, 2019 at 11:11:01 AM UTC-8, Sam Tobin-Hochstadt > wrote: >> >> Any of these solutions need a O(N) traversal of the data. That's >> because we need to do a full traversal to be sure we got an actual >> (Listof String) from read-json -- there's no way around it. >> >> Sam >> >> On Thu, Feb 28, 2019 at 2:04 PM Brian Craft wrote: >> > >> > I would think there'd be a large performance issue, as well, due to >> > needing an O(N) walk of the data. I'm having type checker issues with >> > (time), so haven't tested it, but maybe (cast) will get me past those. >> > >> > Thanks! >> > >> > On Monday, February 25, 2019 at 4:26:52 PM UTC-8, Philip McGrath wrote: >> >> >> >> An alternative to figuring out how to satisfy the type checker is to use >> >> `cast`, e.g.: >> >> #lang typed/racket >> >> (require typed/json) >> >> (string-join >> >> (cast >> >> (string->jsexpr >> >>"[\"The\",\"quick\",\"brown\",\"fox\",\"...\"]") >> >> (Listof String))) >> >> >> >> Obviously this has pros and cons, the main pro being that it runs. The >> >> biggest con, in my view, is that you effectively are dropping into >> >> untyped world. If you figure out how to satisfy the type checker, you get >> >> assurance that your code is well-typed, which is presumably what you want >> >> if your using Typed Racket in the first place. Using `cast` means that >> >> you are responsible for making sure that expression has the type you say >> >> it does, without help from Typed Racket, or you will get a runtime error. >> >> For example, I often forget that `read-json` might return `eof` rather >> >> than a `JSExpr`. Also, `cast` uses the contract machinery, which can >> >> carry performance costs. >> >> >> >> But the fact that it runs is not a small benefit, especially if it lets >> >> you fill in other parts of your program and come back to remove the >> >> `cast` later. It also lets you take advantage of Typed Racket to generate >> >> any complicated runtime checks. >> >> >> >> -Philip >> >> >> >> >> >> On Mon, Feb 25, 2019 at 6:49 PM wrote: >> >>> >> >>> A JSExpr is one of a couple of things: >> >>> >> >>> - A list >> >>> - A hash with symbol keys >> >>> - A number >> >>> - A string >> >>> - A boolean >> >>> - Null >> >>> >> >>> The (andmap string?) approach implicitly assumes you're giving it a >> >>> list. But it might be something else instead, so you want this: (and >> >>> (list? js) (andmap string? js)) >> >>> >> >>> On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft wrote: >> >> So, that also gives me a type error: >> >> Type Checker: Polymorphic function `andmap' could not be applied to >> arguments: >> Domains: (-> a b ... b c) (Listof a) (Listof b) ... b >> (-> a c : d) (Listof a) >> Arguments: (-> Any Boolean : String) (U EOF JSExpr) >> >> in: (andmap string? s) >> >> >> On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt >> wrote: >> > >> > I think (andmap string? ...) is probably the easiest way to check that. >> > >> > Sam >> > >> > On Mon, Feb 25, 2019, 6:20 PM Brian Craft wrote: >> >> >> >> In typed racket, parsing a string list gives me a JSExpr, which is a >> >> union. I need to pass it to functions that operate on string lists, >> >> but can't figure out how to please the type checker. Maybe with >> >> occurrence typing? But I don't know how to assert "this is a list of >> >> strings". >> >> >> >> -- >> >> You received this message because you are subscribed to the Google >> >> Groups "Racket Users" group. >> >> To unsubscribe from this group and stop receiving emails from it, >> >> send an email to racket-users...@googlegroups.com. >> >> For more options, visit https://groups.google.com/d/optout. >> >>> >> >>> -- >> >>> You received this message because you are subscribed to the Google >> >>> Groups "Racket Users" group. >> >>> To unsubscribe from this group and stop receiving emails from it, send >> >>> an email to racket-users...@googlegroups.com. >> >>> For more options, visit https://groups.google.com/d/optout. >> > >> > -- >> > You received this message because you are subscribed to the Google Groups >> > "Racket Users" group. >> > To unsubscribe from this group and stop receiving emails from it, send an >> > email to racket-users...@googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, s
Re: [racket-users] how to use union types
Really? A cast is also O(N)? On Thursday, February 28, 2019 at 11:11:01 AM UTC-8, Sam Tobin-Hochstadt wrote: > > Any of these solutions need a O(N) traversal of the data. That's > because we need to do a full traversal to be sure we got an actual > (Listof String) from read-json -- there's no way around it. > > Sam > > On Thu, Feb 28, 2019 at 2:04 PM Brian Craft > wrote: > > > > I would think there'd be a large performance issue, as well, due to > needing an O(N) walk of the data. I'm having type checker issues with > (time), so haven't tested it, but maybe (cast) will get me past those. > > > > Thanks! > > > > On Monday, February 25, 2019 at 4:26:52 PM UTC-8, Philip McGrath wrote: > >> > >> An alternative to figuring out how to satisfy the type checker is to > use `cast`, e.g.: > >> #lang typed/racket > >> (require typed/json) > >> (string-join > >> (cast > >> (string->jsexpr > >>"[\"The\",\"quick\",\"brown\",\"fox\",\"...\"]") > >> (Listof String))) > >> > >> Obviously this has pros and cons, the main pro being that it runs. The > biggest con, in my view, is that you effectively are dropping into untyped > world. If you figure out how to satisfy the type checker, you get assurance > that your code is well-typed, which is presumably what you want if your > using Typed Racket in the first place. Using `cast` means that you are > responsible for making sure that expression has the type you say it does, > without help from Typed Racket, or you will get a runtime error. For > example, I often forget that `read-json` might return `eof` rather than a > `JSExpr`. Also, `cast` uses the contract machinery, which can carry > performance costs. > >> > >> But the fact that it runs is not a small benefit, especially if it lets > you fill in other parts of your program and come back to remove the `cast` > later. It also lets you take advantage of Typed Racket to generate any > complicated runtime checks. > >> > >> -Philip > >> > >> > >> On Mon, Feb 25, 2019 at 6:49 PM wrote: > >>> > >>> A JSExpr is one of a couple of things: > >>> > >>> - A list > >>> - A hash with symbol keys > >>> - A number > >>> - A string > >>> - A boolean > >>> - Null > >>> > >>> The (andmap string?) approach implicitly assumes you're giving it a > list. But it might be something else instead, so you want this: (and (list? > js) (andmap string? js)) > >>> > >>> On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft wrote: > > So, that also gives me a type error: > > Type Checker: Polymorphic function `andmap' could not be applied to > arguments: > Domains: (-> a b ... b c) (Listof a) (Listof b) ... b > (-> a c : d) (Listof a) > Arguments: (-> Any Boolean : String) (U EOF JSExpr) > > in: (andmap string? s) > > > On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt > wrote: > > > > I think (andmap string? ...) is probably the easiest way to check > that. > > > > Sam > > > > On Mon, Feb 25, 2019, 6:20 PM Brian Craft > wrote: > >> > >> In typed racket, parsing a string list gives me a JSExpr, which is > a union. I need to pass it to functions that operate on string lists, but > can't figure out how to please the type checker. Maybe with occurrence > typing? But I don't know how to assert "this is a list of strings". > >> > >> -- > >> You received this message because you are subscribed to the Google > Groups "Racket Users" group. > >> To unsubscribe from this group and stop receiving emails from it, > send an email to racket-users...@googlegroups.com. > >> For more options, visit https://groups.google.com/d/optout. > >>> > >>> -- > >>> You received this message because you are subscribed to the Google > Groups "Racket Users" group. > >>> To unsubscribe from this group and stop receiving emails from it, send > an email to racket-users...@googlegroups.com. > >>> For more options, visit https://groups.google.com/d/optout. > > > > -- > > You received this message because you are subscribed to the Google > Groups "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to racket-users...@googlegroups.com . > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
Any of these solutions need a O(N) traversal of the data. That's because we need to do a full traversal to be sure we got an actual (Listof String) from read-json -- there's no way around it. Sam On Thu, Feb 28, 2019 at 2:04 PM Brian Craft wrote: > > I would think there'd be a large performance issue, as well, due to needing > an O(N) walk of the data. I'm having type checker issues with (time), so > haven't tested it, but maybe (cast) will get me past those. > > Thanks! > > On Monday, February 25, 2019 at 4:26:52 PM UTC-8, Philip McGrath wrote: >> >> An alternative to figuring out how to satisfy the type checker is to use >> `cast`, e.g.: >> #lang typed/racket >> (require typed/json) >> (string-join >> (cast >> (string->jsexpr >>"[\"The\",\"quick\",\"brown\",\"fox\",\"...\"]") >> (Listof String))) >> >> Obviously this has pros and cons, the main pro being that it runs. The >> biggest con, in my view, is that you effectively are dropping into untyped >> world. If you figure out how to satisfy the type checker, you get assurance >> that your code is well-typed, which is presumably what you want if your >> using Typed Racket in the first place. Using `cast` means that you are >> responsible for making sure that expression has the type you say it does, >> without help from Typed Racket, or you will get a runtime error. For >> example, I often forget that `read-json` might return `eof` rather than a >> `JSExpr`. Also, `cast` uses the contract machinery, which can carry >> performance costs. >> >> But the fact that it runs is not a small benefit, especially if it lets you >> fill in other parts of your program and come back to remove the `cast` >> later. It also lets you take advantage of Typed Racket to generate any >> complicated runtime checks. >> >> -Philip >> >> >> On Mon, Feb 25, 2019 at 6:49 PM wrote: >>> >>> A JSExpr is one of a couple of things: >>> >>> - A list >>> - A hash with symbol keys >>> - A number >>> - A string >>> - A boolean >>> - Null >>> >>> The (andmap string?) approach implicitly assumes you're giving it a list. >>> But it might be something else instead, so you want this: (and (list? js) >>> (andmap string? js)) >>> >>> On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft wrote: So, that also gives me a type error: Type Checker: Polymorphic function `andmap' could not be applied to arguments: Domains: (-> a b ... b c) (Listof a) (Listof b) ... b (-> a c : d) (Listof a) Arguments: (-> Any Boolean : String) (U EOF JSExpr) in: (andmap string? s) On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt wrote: > > I think (andmap string? ...) is probably the easiest way to check that. > > Sam > > On Mon, Feb 25, 2019, 6:20 PM Brian Craft wrote: >> >> In typed racket, parsing a string list gives me a JSExpr, which is a >> union. I need to pass it to functions that operate on string lists, but >> can't figure out how to please the type checker. Maybe with occurrence >> typing? But I don't know how to assert "this is a list of strings". >> >> -- >> You received this message because you are subscribed to the Google >> Groups "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send >> an email to racket-users...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "Racket Users" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to racket-users...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
I would think there'd be a large performance issue, as well, due to needing an O(N) walk of the data. I'm having type checker issues with (time), so haven't tested it, but maybe (cast) will get me past those. Thanks! On Monday, February 25, 2019 at 4:26:52 PM UTC-8, Philip McGrath wrote: > > An alternative to figuring out how to satisfy the type checker is to use > `cast`, e.g.: > #lang typed/racket > (require typed/json) > (string-join > (cast > (string->jsexpr >"[\"The\",\"quick\",\"brown\",\"fox\",\"...\"]") > (Listof String))) > > Obviously this has pros and cons, the main pro being that it runs. The > biggest con, in my view, is that you effectively are dropping into untyped > world. If you figure out how to satisfy the type checker, you get assurance > that your code is well-typed, which is presumably what you want if your > using Typed Racket in the first place. Using `cast` means that you are > responsible for making sure that expression has the type you say it does, > without help from Typed Racket, or you will get a runtime error. For > example, I often forget that `read-json` might return `eof` rather than a > `JSExpr`. Also, `cast` uses the contract machinery, which can carry > performance costs. > > But the fact that it runs is not a small benefit, especially if it lets > you fill in other parts of your program and come back to remove the `cast` > later. It also lets you take advantage of Typed Racket to generate any > complicated runtime checks. > > -Philip > > > On Mon, Feb 25, 2019 at 6:49 PM > wrote: > >> A JSExpr is one of a couple of things: >> >> - A list >> - A hash with symbol keys >> - A number >> - A string >> - A boolean >> - Null >> >> The (andmap string?) approach implicitly assumes you're giving it a list. >> But it might be something else instead, so you want this: (and (list? js) >> (andmap string? js)) >> >> On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft wrote: >>> >>> So, that also gives me a type error: >>> >>> Type Checker: Polymorphic function `andmap' could not be applied to >>> arguments: >>> Domains: (-> a b ... b c) (Listof a) (Listof b) ... b >>> (-> a c : d) (Listof a) >>> Arguments: (-> Any Boolean : String) (U EOF JSExpr) >>> >>> in: (andmap string? s) >>> >>> >>> On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt >>> wrote: I think (andmap string? ...) is probably the easiest way to check that. Sam On Mon, Feb 25, 2019, 6:20 PM Brian Craft wrote: > In typed racket, parsing a string list gives me a JSExpr, which is a > union. I need to pass it to functions that operate on string lists, but > can't figure out how to please the type checker. Maybe with occurrence > typing? But I don't know how to assert "this is a list of strings". > > -- > You received this message because you are subscribed to the Google > Groups "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send > an email to racket-users...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to racket-users...@googlegroups.com . >> For more options, visit https://groups.google.com/d/optout. >> > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
An alternative to figuring out how to satisfy the type checker is to use `cast`, e.g.: #lang typed/racket (require typed/json) (string-join (cast (string->jsexpr "[\"The\",\"quick\",\"brown\",\"fox\",\"...\"]") (Listof String))) Obviously this has pros and cons, the main pro being that it runs. The biggest con, in my view, is that you effectively are dropping into untyped world. If you figure out how to satisfy the type checker, you get assurance that your code is well-typed, which is presumably what you want if your using Typed Racket in the first place. Using `cast` means that you are responsible for making sure that expression has the type you say it does, without help from Typed Racket, or you will get a runtime error. For example, I often forget that `read-json` might return `eof` rather than a `JSExpr`. Also, `cast` uses the contract machinery, which can carry performance costs. But the fact that it runs is not a small benefit, especially if it lets you fill in other parts of your program and come back to remove the `cast` later. It also lets you take advantage of Typed Racket to generate any complicated runtime checks. -Philip On Mon, Feb 25, 2019 at 6:49 PM wrote: > A JSExpr is one of a couple of things: > > - A list > - A hash with symbol keys > - A number > - A string > - A boolean > - Null > > The (andmap string?) approach implicitly assumes you're giving it a list. > But it might be something else instead, so you want this: (and (list? js) > (andmap string? js)) > > On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft wrote: >> >> So, that also gives me a type error: >> >> Type Checker: Polymorphic function `andmap' could not be applied to >> arguments: >> Domains: (-> a b ... b c) (Listof a) (Listof b) ... b >> (-> a c : d) (Listof a) >> Arguments: (-> Any Boolean : String) (U EOF JSExpr) >> >> in: (andmap string? s) >> >> >> On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt >> wrote: >>> >>> I think (andmap string? ...) is probably the easiest way to check that. >>> >>> Sam >>> >>> On Mon, Feb 25, 2019, 6:20 PM Brian Craft wrote: >>> In typed racket, parsing a string list gives me a JSExpr, which is a union. I need to pass it to functions that operate on string lists, but can't figure out how to please the type checker. Maybe with occurrence typing? But I don't know how to assert "this is a list of strings". -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users...@googlegroups.com. For more options, visit https://groups.google.com/d/optout. >>> -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
A JSExpr is one of a couple of things: - A list - A hash with symbol keys - A number - A string - A boolean - Null The (andmap string?) approach implicitly assumes you're giving it a list. But it might be something else instead, so you want this: (and (list? js) (andmap string? js)) On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft wrote: > > So, that also gives me a type error: > > Type Checker: Polymorphic function `andmap' could not be applied to > arguments: > Domains: (-> a b ... b c) (Listof a) (Listof b) ... b > (-> a c : d) (Listof a) > Arguments: (-> Any Boolean : String) (U EOF JSExpr) > > in: (andmap string? s) > > > On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt > wrote: >> >> I think (andmap string? ...) is probably the easiest way to check that. >> >> Sam >> >> On Mon, Feb 25, 2019, 6:20 PM Brian Craft wrote: >> >>> In typed racket, parsing a string list gives me a JSExpr, which is a >>> union. I need to pass it to functions that operate on string lists, but >>> can't figure out how to please the type checker. Maybe with occurrence >>> typing? But I don't know how to assert "this is a list of strings". >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Racket Users" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to racket-users...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
That's because you don't necessarily have a list there, so you need to combine it with a list? check. Sam On Mon, Feb 25, 2019, 6:44 PM Brian Craft wrote: > So, that also gives me a type error: > > Type Checker: Polymorphic function `andmap' could not be applied to > arguments: > Domains: (-> a b ... b c) (Listof a) (Listof b) ... b > (-> a c : d) (Listof a) > Arguments: (-> Any Boolean : String) (U EOF JSExpr) > > in: (andmap string? s) > > > On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt > wrote: >> >> I think (andmap string? ...) is probably the easiest way to check that. >> >> Sam >> >> On Mon, Feb 25, 2019, 6:20 PM Brian Craft wrote: >> >>> In typed racket, parsing a string list gives me a JSExpr, which is a >>> union. I need to pass it to functions that operate on string lists, but >>> can't figure out how to please the type checker. Maybe with occurrence >>> typing? But I don't know how to assert "this is a list of strings". >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Racket Users" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to racket-users...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
So, that also gives me a type error: Type Checker: Polymorphic function `andmap' could not be applied to arguments: Domains: (-> a b ... b c) (Listof a) (Listof b) ... b (-> a c : d) (Listof a) Arguments: (-> Any Boolean : String) (U EOF JSExpr) in: (andmap string? s) On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt wrote: > > I think (andmap string? ...) is probably the easiest way to check that. > > Sam > > On Mon, Feb 25, 2019, 6:20 PM Brian Craft > wrote: > >> In typed racket, parsing a string list gives me a JSExpr, which is a >> union. I need to pass it to functions that operate on string lists, but >> can't figure out how to please the type checker. Maybe with occurrence >> typing? But I don't know how to assert "this is a list of strings". >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to racket-users...@googlegroups.com . >> For more options, visit https://groups.google.com/d/optout. >> > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] how to use union types
I think (andmap string? ...) is probably the easiest way to check that. Sam On Mon, Feb 25, 2019, 6:20 PM Brian Craft wrote: > In typed racket, parsing a string list gives me a JSExpr, which is a > union. I need to pass it to functions that operate on string lists, but > can't figure out how to please the type checker. Maybe with occurrence > typing? But I don't know how to assert "this is a list of strings". > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] how to use union types
In typed racket, parsing a string list gives me a JSExpr, which is a union. I need to pass it to functions that operate on string lists, but can't figure out how to please the type checker. Maybe with occurrence typing? But I don't know how to assert "this is a list of strings". -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
