Type of an expression in haskell -


i'm new haskell , i'm having little bit of trouble understanding of concepts of language.

i have following expression:

\f x → (f x,f 1)

and understanding, can that:

  • at first, can't f because have no information, can anything.

    then judging application of (f x) can it's function of type a->b x::a

    then judging application of (f 1) can of type integer, therefore x same type

then don't understand why whole expression of type:

(integer → b) → integer → (b, b)

i have little guess , i'm going that:

(integer → b) type of function f, receives , integer , returns type b

integer type of x

(b b) type of 2 functions called?

can point me in right direction please? thank you

you correct.

since f applied 1 :: integer, f :: integer -> b.

and since f applied x, x :: integer.

and since result of lambda tuple of applications of f, result type (b, b).

so type of lambda function takes of type of f function takes integer tuple of (b, b).

edit

c b = b

assume b :: t1.

since a applied b, can a :: t1 -> t.

since c takes of type of b (t1) of type of a (t1 -> t) result of application of a b (t), can c :: t1 -> (t1 -> t) -> t.


Comments

Post a Comment

Popular posts from this blog

c# - Update a combobox from a presenter (MVP) -

i using mvp in project, new in mvp. have 2 comboboxes. when select option in combobox, combobox should filled new data. this action in presenter. view 'view1' in presenter, , introduced combobox1 , combobox2 properties in 'view1', because need 'datasource', 'displaymember', 'valuemember' , 'refresh()' in method below. but, when using pattern, enough send property like public string combobox2 { { return combobox1.selectedvalue.tosstring(); } } into presenter not whole combobox. how can solve problem? public void onselectedindexchangedcombobox1() { if (view1.combobox1.selectedindex == -1) { return; } datatable dt = tools.getdatatable("a path"); var query = (from o in dt.asenumerable() o.field<string>("afield") == farmerview.combobox1.selectedvalue.tostring() orderby o.field<string>("anotherfield") select...
Read more

android - Unable to generate FCM token from dynamically instantiated Firebase -

our business logic requires instantiate firebase during runtime. fetch firebase credentials (app id, api key etc.) default firebase location after knowing user's public key , create firebase instance using credentials. this means there 2 firebase instances used within app: the default "index" firebase gives credentials second the actual firebase intend use point forward the second firebase initialised this: firebaseapp app = firebaseapp.initializeapp(<context>, <options>, <app_label>); our problem traditional method of retrieving fcm token using firebaseinstanceidservice , ontokenrefresh() fails since ontokenrefresh() method called first firebase instance. directly calling string token = firebaseinstanceid.getinstance(app).gettoken(); returns null never ready when called. have tried polling test if token generated @ point. no luck. how can generate fcm token reliably firebase instance instantiated during runtime? i...
Read more

How to put a lock and transaction on table using spring 4 or above using jdbcTemplate and annotations like @Transactional? -

i trying put lock on table while writing on table , if happened in between roll-back . trying convert below code lock table test_g1 read; lock table test_g write; -- begin; start transaction; insert test_g1 values(143); insert test_g values(145); select * test_g1; select * test_g; rollback; select * test_g; unlock tables; how convert above code @transactional spring jdbctemplate code? @transactional(rollbackfor={dataaccessexception.class}) public void test(){ jdbctemplate.execute("insert test1 (id, nam) values (4, 'a')"); throw new dataaccessexception("error") { }; } here trying throw error, insert statement should rollback it's not happening . thanks edit-1 attaching code , doing in jdbcdaoimpl.java , mentioned problem comment above test() . app.java package com.cgiri.javabrains.spring4; import org.springframework.beans.factory.annotation.autowired; import org.springframework.context.applic...
Read more