function - Int and Num type of haskell -


i have below code take args set offset time.

setoffsettime :: (ord a, num b)=>[a] -> b setoffsettime [] = 200 setoffsettime (x:xs) = read x::int

but compiler says "could not deduce (b ~ int) context (ord a, num b) bound type signature setoffsettime :: (ord a, num b) => [a] -> b

also found not use 200.0 if want float default value. compilers says "could not deduce (fractional b) arising literal `200.0'"

could 1 show me code function (not in prelude) takes arg store variable can use in other function? can in main = do, hope use elegant function achieve this. there global constant stuff in hasekll? googled it, seems not.

i wanna use haskell replace of python script although not easy.

i think type signature doesn't quite mean think does:

setoffsettime :: (ord a, num b)=>[a] -> b

what says "if give me value of type [a], type a you choose member of ord type class, give value of type b, type b you choose member of num type class". caller gets pick particular types a , b used each time setoffsettime called.

so trying return value of type int (or float, or particular type) doesn't make sense. int indeed member of type class num, it's not any member of type class num. according type signature, should able make brand new instance of num you've never seen before, import setoffsettime module, , call value of new type.

to come acceptable return value, can only use functions likewise return arbitrary num. can't use functions of particular concrete types.

existential types mechanism allowing callee choose value type variable (and caller has written work regardless of type is), that's not want getting while you're still learning.


Comments

Post a Comment

Popular posts from this blog

Why does Ruby on Rails generate add a blank line to the end of a file? -

running rails generate controller foo home results in: class foocontroller < application controller def home end end (there's nothing on line in actual file, blank line) is there purpose blank line? it's common use newline indicate end of line, last line. many editors (like vi, use) add in newline silently. consensus text files (especially in unix world) should end in newline, , there have been problems historically if wasn't present. why should text files end newline? the tool used count lines in file "wc" counts newlines in file, without trailing newline show 3 instead of 4. it improves readability of templates used in generator. consider: https://github.com/rails/rails/blob/master/railties/lib/rails/generators/rails/controller/templates/controller.rb to remove trailing newline, template have last line of: end<% end -%> instead of: end <% end -%> that seems less readable me. the discussion below refers ...
Read more

keyboard - Smiles and long press feature in Android -

i've created android keyboard. how add features inserting smilies, , using long keypresses display symbols? to create long-press behavior allows select several options pop-up menu, follow guide (specifically pop-up menu section): http://developer.android.com/guide/topics/ui/menus.html smileys (also known emoticons) combination of keys, understood programs , parsed same way. have do, when clicks smiley face on keyboard, simulate pressing of key combination matching emoticon. example, when clicks smiley, should simulate key presses ':' , ')' :). here's list of emoticons: http://en.wikipedia.org/wiki/list_of_emoticons
Read more

node.js - Bad Request - node js ajax post -

i'm using express 3.0 , node v0.11.0. have button submits form , i'm using ajax post data json object node server. client code is: $('#contact').submit(function(e) { console.log('submit called'); var formdata = json.stringify($('form').serializeobject()); console.log(formdata); $.ajax({ url: "http://localhost:3000/savedata/", type: "post", datatype: 'json', data: {objectdata: formdata}, contenttype: "application/json", complete: function() { console.log('process complete'); }, success: function(data) { console.log('process sucess'); }, error: function() { console.log('process error'); }, }); return false; }); then on server: var express = require('express'); var app = express(); app.set('views', __dirname + '/views'); app.set('view engine', 'jade'); app.use(express.bodyparser());...
Read more