Re: [Nix-dev] How to escape $'\t' in Nix multi-line string?

2017-04-30 Thread Layus 

On 30/04/17 20:04, Bjørn Forsman wrote:

On 30 April 2017 at 19:53, Profpatsch  wrote:

On 17-04-30 03:07pm, Bjørn Forsman wrote:

On 30 April 2017 at 15:01, Bjørn Forsman  wrote:

Hi all,

I'm stuck trying to pass $'\t' to bash via Nix multi-line strings:

nix-repl> ''cut -d $'\t' -f 1''
error: syntax error, unexpected $undefined, expecting IND_STR or
DOLLAR_CURLY or IND_STRING_CLOSE, at (string):1:10

Oh, it was only missing double single-quotes before the dollar sign.

What tripped me was that the documentation says ${ is special in
strings, not $'.

How should we improve the manual in this regard?

Sure. But I'm also quite interested in knowing why $' needs escaping,
especially when $ ' (space between) does not.
I guess the answer resides at 
https://github.com/NixOS/nix/blob/2f21d522c28b1e902bd7f0b5b9e7523975102d81/src/libexpr/lexer.l#L159-L162


To be efficient, we accept any $ followed by something that's not a 
opening curly brace ('{') as normal string content. But we cannot accept 
"$'", as the last single quote could be part of a double single-quote, 
thus ending the multiline-string.


The corner case of a single single-quote following a dollar requires a 
lookahead and has been left out (forgotten ? :-)) in the lexer.


For advanced usages of multiline-strings, I refer you to the tests in 
nix source code : 
https://github.com/NixOS/nix/blob/master/tests/lang/eval-okay-ind-string.nix


-- Layus.
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Re: [Nix-dev] How to escape $'\t' in Nix multi-line string?

2017-04-30 Thread Bjørn Forsman 
On 30 April 2017 at 19:53, Profpatsch  wrote:
> On 17-04-30 03:07pm, Bjørn Forsman wrote:
>> On 30 April 2017 at 15:01, Bjørn Forsman  wrote:
>> > Hi all,
>> >
>> > I'm stuck trying to pass $'\t' to bash via Nix multi-line strings:
>> >
>> > nix-repl> ''cut -d $'\t' -f 1''
>> > error: syntax error, unexpected $undefined, expecting IND_STR or
>> > DOLLAR_CURLY or IND_STRING_CLOSE, at (string):1:10
>>
>> Oh, it was only missing double single-quotes before the dollar sign.
>>
>> What tripped me was that the documentation says ${ is special in
>> strings, not $'.
>
> How should we improve the manual in this regard?

Sure. But I'm also quite interested in knowing why $' needs escaping,
especially when $ ' (space between) does not.

- Bjørn
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Re: [Nix-dev] How to escape $'\t' in Nix multi-line string?

2017-04-30 Thread Profpatsch 
On 17-04-30 03:07pm, Bjørn Forsman wrote:
> On 30 April 2017 at 15:01, Bjørn Forsman  wrote:
> > Hi all,
> >
> > I'm stuck trying to pass $'\t' to bash via Nix multi-line strings:
> >
> > nix-repl> ''cut -d $'\t' -f 1''
> > error: syntax error, unexpected $undefined, expecting IND_STR or
> > DOLLAR_CURLY or IND_STRING_CLOSE, at (string):1:10
> 
> Oh, it was only missing double single-quotes before the dollar sign.
> 
> What tripped me was that the documentation says ${ is special in
> strings, not $'.

How should we improve the manual in this regard?

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