I'm trying to implement something similar to a hash table in ML, but i want to use lists as keys. I think I could use the ORD_MAP structure, but I want to provide my own structure for the ORD_KEY signature, so that I can use lists as ord_keys, but I cant find a way to do it. How could it be done?
ORD_MAP and ORD_KEY are signatures. If you want to be able to use a map, you'll need a specific implementation. For example:
structure Key =
struct
type ord_key = int
val compare = Int.compare
end
structure Map = RedBlackMapFn (Key)
Then, you can do:
- Map.singleton (1, "foo");
val it = - : string map
- Map.find (it, 1);
val it = SOME "foo" : string option
-
Hope that helps! The documentation on these interfaces is:
http://www.smlnj.org/doc/smlnj-lib/Manual/toc.html
An example that I think answers your question lies at cornell's university lecture here:
Cornell's Lecture
Related
I have a hash map which acts as store of objects - where key is class name & value is object
store = {} of String => Type
store["Animal"]= Animal.new
store["Book"]= Book.new
store["Car"]= Car.new
Here class is unknown to me, which means i can't use union type. Please tell me how to solve this problem ?
I am trying to create a wrapper around hash map for storage of objects, which will save object & return object by key.
Update 1
Classes will be passed as a parameter - like this
add_in_store(Animal)
add_in_store(Person)
Update 2
Crystal play link of what i am trying to do - https://play.crystal-lang.org/#/r/8lwx
Solution of problem doesn't have to be in same way as what i m doing. It can be with any other approach like using proc or macro etc.
Hash is a generic type, to wrap it in a way where you cannot or don't want to restrict the possible types of the generic arguments, you should make your wrapper itself generic.
class Store(V)
#store = {} of String => V
def add(name, value : V)
#store[name] = value
end
end
Then the consumer of your wrapper has to give the possible types.
I am trying to use a string ('npcName') as a variable name. So far I have tried casting dialogMap into a DynamicAccess object, but it gives me the error 'Invalid array access' when I try this:
var npcName:String = 'TestNPC';
var casted = (cast Registry.dialogMap:haxe.DynamicAccess<Dynamic>);
var tempname = casted[root.npcName[0].message];
trace(tempname);
'dialogMap' is an empty map which I want to fill like so:
Registry.dialogMap['message'] = root.npcName[0].message;
How can I use npcName, a string, in the above line of code? Is there a way to transform the string into something usable? Any help would be appreciated.
The haxe.DynamicAccess doesn't have array access (like map[key]), but is an abstract type for working with anonymous structures that are intended to hold collections of objects by the string key. It is designed to work with map.get(key) and map.set(key). It is basically a nicer wrapper around Reflect.field and Reflect.setField and does some safety checks with Reflect.hasField.
var variable = "my_key";
var value = 123;
var dynamicMap = new haxe.DynamicAccess<Dynamic>();
dynamicMap.set(variable, value);
I'm noticing you are doing very much cast and dynamic, so untyped code, which is a bit of contradiction in a typed language. What is the actual type of dialogMap?
Not sure you are aware of it but, Haxe has its own maps, which are fully typed, so you don't need casts.
var map = new Map<String, Int>();
map[variable] = value;
I think this article helps understanding how to work with dynamic (untyped) objects.
Tip; for testing such small functionalities you can doodle around on the try.haxe site : http://try.haxe.org/#4B84E
Hope this helps, otherwise here is some relevant documentation:
http://api.haxe.org/haxe/DynamicAccess.html
https://haxe.org/manual/std-reflection.html
https://haxe.org/manual/types-dynamic.html
http://code.haxe.org/category/beginner/string-variable-reflection.html
I know I'm missing something obvious here. I'm trying to extract values from TitanDB using Gremlin in order to compare them within Groovy.
graph = TinkerFactory.createModern()
g = graph.traversal(standard())
markoCount = g.V().has('name','marko').outE('knows').count()
lopCount = g.V().has('name','lop').outE('knows').count()
if(markoCount > lopCount){
// Do something
}
But apparently what I'm actually (incorrectly) doing here is comparing traversal steps which obviously won't work:
Cannot compare org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.DefaultGraphTraversal with value '[TinkerGraphStep(vertex,[name.eq(marko)]), VertexStep(OUT,[knows],edge), CountGlobalStep]' and org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.DefaultGraphTraversal with value '[TinkerGraphStep(vertex,[name.eq(lop)]), VertexStep(OUT,[knows],edge), CountGlobalStep]'
I'm having the same issue extracting values from properties for use in Groovy as well. I didn't see anything in the docs indicating how to set raw values like this.
What is needed to return actual values from Gremlin that I can use later in my Groovy code?
Figured it out, I needed next():
graph = TinkerFactory.createModern()
g = graph.traversal(standard())
markoCount = g.V().has('name','marko').outE('knows').count().next()
lopCount = g.V().has('name','lop').outE('knows').count().next()
if(markoCount > lopCount){
// Do something
}
I have a cache that looks like this:
Key: UUID
Value: Array[Long]
I want to get the key corresponding to a specific value. How does the where-part look like?
I have tried "value = ?" and "_value = ?" but these obviously doesnt work.
Yo!
What do you mean by Array[Long]? Is it just long[] or may be you are using Scala?
The simplest (but not the most effective) way would be using a scan query with predicate (docs here).
To achieve the best performance it is preferable to have your value indexed, so I'd recommend to have a special wrapper class for your array like this:
class MyArray implements Comparable<MyArray>, Serializable {
private long[] arr;
// implement compareTo,hashCode,equals
#GridCacheQuerySqlField(index = true)
public MyArray indexedArray() {
return this;
}
}
then the query will look like
"indexedArray = ?"
where as parameter you have to pass MyArray instance. It is a bit dirty way to index value but this is the only way right now.
By the way column names for cache key and value in SQL are _key and _val but not _value and you can write queries like
"_val = ? and _key > ?"
of course you have to make sure that your key and value at least implement hashCode and equals correctly, implementing Comparable is preferable.
I have a list AllIDs:
List<IAddress> AllIDs = new List<IAddress>();
I want to do substring operation on a member field AddressId based on a character "_".
I am using below LINQ query but getting compilation error:
AllIDs= AllIDs.Where(s => s.AddressId.Length >= s.AddressId.IndexOf("_"))
.Select(s => s.AddressId.Substring(s.AddressId.IndexOf("_")))
.ToList();
Error:
Cannot implicitly convert type 'System.Collections.Generic.List<string>' to 'System.Collections.Generic.List<MyCompany.Common.Users.IAddress>'
AllIDs is a list of IAddress but you are selecting a string. The compiler is complaining it cannot convert a List<string> to a List<IAddress>. Did you mean the following instead?
var substrings = AllIDs.Where(...).Select(...).ToList();
If you want to put them back into Address objects (assuming you have an Address class in addition to your IAddress interface), you can do something like this (assuming the constructor for Address is in place):
AllIDs = AllIDs.Where(...).Select(new Address(s.AddressID.Substring(s.AddressID.IndexOf("_")))).ToList();
You should also look at using query syntax for LINQ instead of method syntax, it can clean up and improve the readability of a lot of queries like this. Your original (unmodified) query is roughly equivalent to this:
var substrings = from a in AllIDs
let id = a.AddressId
let idx = id.IndexOf("_")
where id.Length >= idx
select id.Substring(idx);
Though this is really just a style thing, and this compiles to the same thing as the original. One slight difference is that you only have to call String.IndexOf() one per entry, instead of twice per entry. let is your friend.
Maybe this?
var boundable =
from s id in AllIDs
where s.AddressId.Length >= s.AddressId.IndexOf("_")
select new { AddressId = s.AddressId.Substring(s.AddressId.IndexOf("_")) };
boundable = boundable.ToList();