Define an operator for FileNameJoin

Question

When I join file names, it's inconvenient to use FileNameJoin. The workaround is to use <> instead, however <> is not exactly like FileNameJoin.

I tried to define an operator . It just doesn't work. If I can define it, I can use it to construct file name like this, "dir1" "dir2" <> "file".

In:

x_ < /> y_ := FileNameJoin[{x, y}]

Out:

Syntax::sntxf: "x_<" cannot be followed by "/>y_".

This is what I do, however I got an error. How can I fix it?

it's possible to define new operators using the Notations` package (see other answers for details). But in your case maybe you just want an alias, say FNJ and then you can use x~FNJ~y?The notations all work from box forms, which can cause issues if you embed them in a package. — b3m2a1, May 31 '17 at 16:27
@MB1965, I prefer </>, because it's like <>, but it can add /(path separator) automatically. Thanks, I will try it with Notations`. — webcpu, May 31 '17 at 16:50
Perhaps you could choose an operator without built-in meanings from the tutorial Operators without Built-in Meanings — Carl Woll, May 31 '17 at 17:40
E.g., TildeTilde = FileNameJoin@*List: http://i.stack.imgur.com/XT6Jg.png — Michael E2, May 31 '17 at 17:43

m_goldberg · Accepted Answer · 2017-05-31T23:09:26.697

5

Suppose you were to choose TildeTilde as Michael E2 suggests. Then you don't need the Symbol Package since ≈ has interpretation as an operator already built-in.

TildeTilde[names___] := FileNameJoin[{names}]

Then

TildeTilde[$HomeDirectory, "Desktop", "my_file.dat"]

gives me

"/Users/oldmg/Desktop/my_file.dat"

and more to the point,

$HomeDirectory ≈ "Desktop" ≈ "my_file.dat"

"/Users/oldmg/Desktop/my_file.dat"

There is an input alias for ≈. You can type Esc+~+~+Esc to get ≈. Input aliases seem be defined for most (maybe all?) of the operators with no built-in meaning.

edited May 31 '17 at 23:09

answered May 31 '17 at 22:01

m_goldberg

107,779
16
103
257

1

No need to add an alias for \[TildeTilde], it already works. – Carl Woll May 31 '17 at 22:10
@CarlWoll. +1 I should have checked the docs. It looks like all the unassigned operator symbols have input aliases. I'll update my answer. – m_goldberg May 31 '17 at 22:32
2

Note that you can use WolframLanguageData (or EntityValue) to find out what the keyboard shortcuts are, e.g., WolframLanguageData["TildeTilde", "KeyboardShortcuts"] – Carl Woll May 31 '17 at 23:06
@CarlWoll. That seems like more trouble than consulting the Documentation Center. – m_goldberg May 31 '17 at 23:11
However, if you wanted to verify that all operators in a list have an input alias, it would be a lot easier to use WolframLanguageData than the Documentation Center. – Carl Woll May 31 '17 at 23:15

Mr.Wizard · Answer 2 · 2017-06-01T19:58:33.580

3

I favor the method m_goldberg shows but an alternative is Rojo's SubscriptBox method from Is it possible to define custom compound assignment operators like ⊕= similar to built-ins +=, *= etc?

MakeExpression[
  RowBox[arg : {_, PatternSequence[SubscriptBox["<>", "/"], _] ..}], 
  StandardForm
] := 
  MakeExpression @ RowBox[{"FileNameJoin", "[", "{", ##, "}", "]"}] & @@ 
    Riffle[arg[[;; ;; 2]], ","]

Now:

To enter this operator in Windows type < > (Ctrl+-) / →

edited Jun 01 '17 at 19:58

answered Jun 01 '17 at 00:10

Mr.Wizard

271,378
34
587
1,371

How to type <>/ ? I tried to use the result of SubscriptBox["<>", "/"] // InputForm, however it doesn't work. – webcpu Jun 01 '17 at 08:01
1

@UnchartedWorks I added the exact key presses needed in Windows. – Mr.Wizard Jun 01 '17 at 19:59

Define an operator for FileNameJoin

2 Answers2