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[Mark Hills <Mark.Hills AT cwi.nl>]

Hi Daniele,

In the parser we are using in our work on PHP, a string such as this gives us 
back a special form of string which is actually a list of string pieces, each 
of which is an individual expression. So, you would get back a list of a 
string literal "Hello ", an expression $x, and a string literal "!". If you 
do it this way, you also don't need to worry about the distinction between 
single-quoted and double-quoted strings inside the semantics, the parser can 
give you the right representation. The question would be whether you could 
define such syntax rules inside K (that I cannot answer).

Cheers,

Mark

----- Original Message -----
From: "Daniele Filaretti" 
<dfilaretti AT gmail.com>
To: 
k-user AT cs.uiuc.edu
Sent: Friday, February 1, 2013 2:25:18 PM
Subject: [K-user] resolving variable names inside double quoted strings (as   
  in PHP)

Hi all,

In PHP (the language I'm trying to define in K) when a variable name occurs 
in a string (variable names always start with $) the value of that variable 
is found in the environment and printed into the string. For example:

> $x = "Daniele";
> echo "Hello $x!"
> 
> out>> "Hello Daniele!"

Until now I ignored this in my definition - i.e., I'm using builtin strings 
that K offer, and I can achieve the same with (that is also legal in PHP):

> $x = "Daniele";
> echo "Hello " . $x . "!"
> 
> out>> "Hello Daniele!"

However, I noticed that the feature is heavily used (of course, as it's a 
very handy shortcut), so I decided to add it. 

I'm currently having a look at the C definition by Chucky Ellison, as I think 
something similar has to be done for C's 'printf". However, it seems that 
their solution is very low level (scanning a string character by character 
and defining some kind of state machine I guess), and perhaps I don't need 
that level of detail.

Ideally, all I need is just something like a string tokenizer. 
For example if my string is 

> "Hello $x!"

I would like to obtain a list (containing strings and variables) :

> ["Hello", $x, "!"]

with this list I could easily print the elements that are already strings, 
and evaluate the variable names before printing them as well (using my 
already defined printing function for strings -- sending to it the elements 
of my list one by one).

Any ideas? Comments? Suggestions?  

Thanks a lot to everyone!

Cheers, 
Daniele
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