Re: [nant-dev] SUMMARY: Expression Syntax

Ian MacLean Sun, 07 Dec 2003 09:25:41 -0800

This is one of the more compelling arguments for me. I'm leaning towards option A with {} used everywhere - for clarity and consistency.- and ease of syntax highlighting.

Ian
Jaroslaw Kowalski wrote:

One more thing which I forgot:

Q1 there's a problem where:
B: ${$propertyname} and ${propertyname}
C: ${${propertyname}} and ${propertyname}
both are legal forms to express a property. Variant A has no such problem.

Jarek

----- Original Message ----- From: "Jaroslaw Kowalski" <[EMAIL PROTECTED]> To: "Scott Hernandez" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Saturday, December 06, 2003 11:40 AM Subject: [nant-dev] SUMMARY: Expression Syntax
Hi Scott,

As you requested, here's a summary of expression evaluator discussion:
Ian, Gert, Martin - can you please correct me if I'm wrong anywhere in the
summary.
========================================================
There are 2 questions:
QUESTION 1:
How should expressions be written?
A) <echo message="aaa" if="${length(propertyname)=3}" />
B) <echo message="aaa" if="${length($propertyname)=3}" />
C) <echo message="aaa" if="${length(${propertyname})=3}" />
Variant A - is clean and compatible with current approach to accessing
properties. Properties can still be accessed as ${propertyname}.
This may have the following problems:

- it may be hard to distinguish between property and function names
because

they only differ by () (Java, C#, C++ also have this problem). - we may no be able to access some properties (like nant.task.cvs-checkout.location) because they contain dashes which cannot

be

distinguished from "minus" operator. "a-b" could either be "a" MINUS "b"

or

a property named "a-b". Fortunately there are only 6 such properties in

NAnt
(so this could be quite easily resolved):
nant.tasks.cvs-update
nant.tasks.cvs-checkout
nant.tasks.delay-sign
nant.tasks.cvs-update.location
nant.tasks.cvs-checkout.location
nant.tasks.delay-sign.location
There was a suggestion to disallow such property names and formally define
them as:
property name => identifier { DOT identifier } *
identifier => [a-zA-Z_][a-zA-Z0-9_]*
In English:
"property name" is a sequence of "identifiers" separated by dots
"identifier" starts with a latin letter or an underscore and contains only
letters, digits underscores (like in C#, C++, Java, VB, JavaScript...)
- we may not be compatible with property names which are numeric. I was
told

that currently a property can be named "1234". There seems to be an agreement that this should be disallowed asap. I suggest that we disallow properties containing dashes in their names at the same time. - one could always use use propertyvalue('propertyname') function to

access

weird-names properties

Variant B - prefix properties with '$' - similar to PERL

- is still quite clean, yet there are some dollars starting to appear - this solves the first problem (the properties can be distinguished

because
they are prefixed with $)
- accessing properties with dashes can still be tricky:
$property-name-with-dashes  // access property
$property-name-with-dashes(1) // $property-name-with MINUS dashes(1)
Variant C - enclose properties in ${...}
- it's difficult to read, especially when using proportional font,
- it's unambiguous
- no problem accessing any property
Opinions on Q1:
Jarek: A
Martin: A
Ian: A or B
Gert: B or C
QUESTION 2: Should we always require ${} (or anything else we use for quoting) to be written around expressions, or should we allow unquoted expressions in
some
places?

Variant A (quote all expressions)
<if test="${length(someproperty)=3}">
   ...
</if>
<echo message="test" if ="${length(someproperty)=3}" />
<echo message="test" unless ="${length(someproperty)=3}" />
- it's simple - you ALWAYS use quotes around expressions (both embedded in strings and stand-alone) - you can easily spot the expressions in your build file - this may allow for easy implementation of syntax highlighting (actually
I
already did this for VIM)
Variant B: allow for unquoted expressions in some places where non-string
values are expected:
Like "<if test="..." /> <... if="..." /> <... unless="..." />
<if test="length(someproperty)=3">
   ...
</if>
<echo message="test" if="length(someproperty)=3" />
<echo message="test" unless="length(someproperty)=3" />
- this is somewhat more readable (less dollars)
- it may be hard to find expressions in the build file.
- it may not be clear when to use quotes and when not to use them
Variant C: skip quotes for <if test="..." /> - keep for everything else

- this is implemented in "test1"

Opinions on Q2:
Jarek: A
Martin: A
CURRENT STATUS:
1. Expression evaluator is in CVS in branch "EE-patches"
2. It implements variants: Q1:A and Q2:C
A binary release of this is available at

http://jaak.sav.net/nant-ee/nant-ee-test1.zip

It contains some test cases written as a build file.

Jarek
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-- Ian MacLean, Developer, ActiveState, a division of Sophos http://www.ActiveState.com


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Re: [nant-dev] SUMMARY: Expression Syntax

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