scala - SBT Output for Kind Type -

-

with respect type theory, field of mathematics , computer science both tend use same notation kinds , kinds construction, namely symbols:

  1. *
  2. ->

haskell adopts notation:

prelude> :k maybe maybe :: * -> *

but in sbt, get:

scala> :k option scala.option's kind f[+a]

the haskell way easier understand directly matches literature on type theory. why did sbt not use * , -> notation? information can see being imparted sbt way type variance.

try verbose flag (-v)

scala> :k -v option scala.option's kind f[+a] * -(+)-> * type constructor: 1st-order-kinded type.

some more info:

http://docs.scala-lang.org/scala/2.11/ (ctrl+f :kind)

https://github.com/scala/scala/pull/2340


Comments

Post a Comment

Popular posts from this blog

Java 3D LWJGL collision -

-
i making 3d java game lwjgl library, , wondering how add collision detection, player not go through models. i using obj models. here objloader class, loads models: package renderengine; import java.io.bufferedreader; import java.io.file; import java.io.filenotfoundexception; import java.io.filereader; import java.util.arraylist; import java.util.list; import models.rawmodel; import org.lwjgl.util.vector.vector2f; import org.lwjgl.util.vector.vector3f; public class objloader { public static rawmodel loadobjmodel(string filename, loader loader){ filereader fr = null; try { fr = new filereader(new file("res/"+filename+".obj")); } catch (filenotfoundexception e) { system.err.println("couldn't load file!"); e.printstacktrace(); } bufferedreader reader = new bufferedreader(fr); string line; list<vector3f> vertices = new arraylist<vector3f...
Read more

spring - SubProtocolWebSocketHandler - No handlers -

-
i have ugly error during deploying spring app on jboss. 18:11:16,025 error [org.apache.catalina.core.containerbase.[jboss.web].[default-host].[/consumer]] (msc service thread 1-7) exception sending context initialized event listener instance of class org.springframework.web.context.contextloaderlistener: org.springframework.context.applicationcontextexception: failed start bean 'subprotocolwebsockethandler'; nested exception java.lang.illegalargumentexception: no handlers @ org.springframework.context.support.defaultlifecycleprocessor.dostart(defaultlifecycleprocessor.java:176) [spring-context-4.1.3.release.jar:4.1.3.release] @ org.springframework.context.support.defaultlifecycleprocessor.access$200(defaultlifecycleprocessor.java:51) [spring-context-4.1.3.release.jar:4.1.3.release] @ org.springframework.context.support.defaultlifecycleprocessor$lifecyclegroup.start(defaultlifecycleprocessor.java:346) [spring-context-4.1.3.release.jar:4.1.3.release] @ org.s...
Read more

methods - python can't use function in submodule -

-
my folder structure this: pythonstuff/ program.py modulea/ __init__.py foo.py bar.py here's code bar.py : def hello(): print("hello, world!") here's code program.py : #!/usr/bin/env python3 modulea import bar bar.hello() i run $ python3 program.py somehow error: file "program.py", line 3, in <module> bar.hello() attributeerror: 'module' object has no attribute 'hello' edit: __init__.py file empty. edit2: after trying realized had bar.py in root directory contained hello() method. bar.py in modulea/ directory empty. add it import os __all__ = [] module in os.listdir(os.path.dirname(__file__)): if module != '__init__.py' , module[-3:] == '.py': __all__.append(module[:-3]) the init .py files required make python treat directories containing packages; done prevent directories common name, such string, unintentionally hiding v...
Read more