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Today's Topics:

   1.  It needs a binder? (Alexander Chen)
   2. Re:  It needs a binder? (Dániel Arató)


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Message: 1
Date: Tue, 28 Apr 2020 21:21:16 +0200 (CEST)
From: Alexander Chen <alexan...@chenjia.nl>
To: beginners@haskell.org
Subject: [Haskell-beginners] It needs a binder?
Message-ID: <349773461.111559.1588101675...@ichabod.co-bxl>
Content-Type: text/plain; charset="utf-8"

Hi,

binder.hs

i:: Num a => a

prelude>:l binder.hs
typed_checked.hs:1:1: error:
    The type signature for ‘i’ lacks an accompanying binding
  |
1 | i:: Num a=> a   | ^

binder.hs

i:: Num a => a
i = 2

prelude>:l binder.hs

[1 of 1] Compiling Main             
Ok, one module loaded.

Why does it need a binder to make it work?
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Message: 2
Date: Wed, 29 Apr 2020 10:46:13 +0200
From: Dániel Arató <exitcons...@gmail.com>
To: Alexander Chen <alexan...@chenjia.nl>,  The Haskell-Beginners
        Mailing List - Discussion of primarily beginner-level topics related
        to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] It needs a binder?
Message-ID:
        <cahvkd2+qk3yo_papekgjoto+jvldwhfbpfeexbzucfqugzm...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Using classic C/C++/Java terms what you're doing in the first version is
analogous to _declaring_ a function but not _defining_ it, e.g.

// binding_incorrect.c
int i();
// No definition leads to an error

// binding_correct.c
int i() {
    return 0;
}

The error message says that you have declared the type of i to be Num a =>
a, but no corresponding definition was found. That's the reason your second
version compiles fine

On Tue, 28 Apr 2020 at 21:22, Alexander Chen <alexan...@chenjia.nl> wrote:

> Hi,
>
> binder.hs
>
> i:: Num a => a
>
> *prelude>*:l binder.hs
> typed_checked.hs:1:1: error:
>     The type signature for ‘i’ lacks an accompanying binding
>   |
> 1 | i:: Num a=> a   | ^
>
>
> binder.hs
>
> i:: Num a => a
> i = 2
>
> *prelude>*:l binder.hs
> [1 of 1] Compiling Main
> Ok, one module loaded.
>
>
> Why does it need a binder to make it work?
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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