[racket-dev] more general typed/scheme bafflement...
I see that map works on multiple lists in at least one circumstance, e.g. (map + (list 3 4) (list 4 5)). I couldn't get it to work with "list", though, even when I specialized list to a two-argument function: #lang typed/racket (: list2 (All (T) (T T -> (List T T (define (list2 a b) (list a b)) (map list2 '(3 4 5) '(10 11 12)) ==> Type Checker: Polymorphic function map could not be applied to arguments: Domains: (a -> c) (Pairof a (Listof a)) (a b ... b -> c) (Listof a) (Listof b) ... b Arguments: (All (T) (T T -> (List T T))) (List Positive-Byte Positive-Byte Positive-Byte) (List Positive-Byte Positive-Byte Positive-Byte) in: (map list2 (quote (3 4 5)) (quote (10 11 12))) Is there some easy fix here? Also, I am deeply confused by the second of those domains, that makes it appear that I'm supposed apply map to a bunch of lists and then to a bare "b". John smime.p7s Description: S/MIME cryptographic signature _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] more general typed/scheme bafflement...
John, You had an easy time with + because it is monomorphic. You are having trouble applying one polymorphic function (map) to another (list or list2). Instantiate one or both functions explicitly, and Typed Racket won't get confused by the guesswork. Also, T ... i in a type does not mean T ... followed by i. It means T ... *indexed* by i. It's clarifying what the ... ranges over. Carl Eastlund On Tue, Jun 7, 2011 at 7:16 PM, John Clements wrote: > I see that map works on multiple lists in at least one circumstance, e.g. > (map + (list 3 4) (list 4 5)). I couldn't get it to work with "list", > though, even when I specialized list to a two-argument function: > > #lang typed/racket > > (: list2 (All (T) (T T -> (List T T > (define (list2 a b) (list a b)) > > (map list2 '(3 4 5) '(10 11 12)) > > ==> Type Checker: Polymorphic function map could not be applied to arguments: > Domains: (a -> c) (Pairof a (Listof a)) > (a b ... b -> c) (Listof a) (Listof b) ... b > Arguments: (All (T) (T T -> (List T T))) (List Positive-Byte Positive-Byte > Positive-Byte) (List Positive-Byte Positive-Byte Positive-Byte) > in: (map list2 (quote (3 4 5)) (quote (10 11 12))) > > Is there some easy fix here? > > Also, I am deeply confused by the second of those domains, that makes it > appear that I'm supposed apply map to a bunch of lists and then to a bare "b". > > John > > > _ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/dev > _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] more general typed/scheme bafflement...
On Jun 7, 2011, at 4:26 PM, Carl Eastlund wrote: > John, > > You had an easy time with + because it is monomorphic. You are having > trouble applying one polymorphic function (map) to another (list or > list2). Instantiate one or both functions explicitly, and Typed > Racket won't get confused by the guesswork. > > Also, T ... i in a type does not mean T ... followed by i. It means T > ... *indexed* by i. It's clarifying what the ... ranges over. Awesome! Many thanks. Next question. I'm reading sexps from a file, so typed/racket insists that I check their shape before using them. That's fine, but I find myself unable to define the "(Pairof Any (Pairof Any Null)) predicate the way I'd expect it to be defined: (: listoflength2? (Any -> Boolean : (Pairof Any (Pairof Any Null (define (listoflength2? a) (and (pair? a) (pair? (cdr a)) (null? (cddr a => Type Checker: Expected result with filter (((List Any Any) @ a) | (! (List Any Any) @ a)), got filter ((AndFilter (Null @ (cdr cdr) a) ((Pairof Any Any) @ (cdr) a) ((Pairof Any Any) @ a)) | (OrFilter (! Null @ (cdr cdr) a) (! (Pairof Any Any) @ (cdr) a) (! (Pairof Any Any) @ a))) in: (and (pair? a) (pair? (cdr a)) (null? (cddr a))) > This is curious, because the text '(AndFilter (Null @ (cdr cdr) a) ((Pairof Any Any) @ (cdr) a) ((Pairof Any Any) @ a)) ' looks like it's saying exactly what '(Pairof Any (Pairof Any Null))' does. Again, any help appreciated. This typed racket stuff is *way* more fun than the actual grading that the script is supposed to be helping me with... :). John smime.p7s Description: S/MIME cryptographic signature _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] more general typed/scheme bafflement...
On Tue, Jun 7, 2011 at 4:57 PM, John Clements wrote: > > On Jun 7, 2011, at 4:26 PM, Carl Eastlund wrote: > >> John, >> >> You had an easy time with + because it is monomorphic. You are having >> trouble applying one polymorphic function (map) to another (list or >> list2). Instantiate one or both functions explicitly, and Typed >> Racket won't get confused by the guesswork. >> >> Also, T ... i in a type does not mean T ... followed by i. It means T >> ... *indexed* by i. It's clarifying what the ... ranges over. > > Awesome! Many thanks. Next question. I'm reading sexps from a file, so > typed/racket insists that I check their shape before using them. That's > fine, but I find myself unable to define the "(Pairof Any (Pairof Any Null)) > predicate the way I'd expect it to be defined: What you actually want to use here is `define-predicate', which will automatically define the predicate you want given the type. > > (: listoflength2? (Any -> Boolean : (Pairof Any (Pairof Any Null > (define (listoflength2? a) > (and (pair? a) (pair? (cdr a)) (null? (cddr a This definition will eventually typecheck, but not yet. :) -- sam th sa...@ccs.neu.edu _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
