On 2017-05-17 23:43, Mark Wieder via use-livecode wrote:
Yes. In fact it's the areas where they differ that make for a
difficult learning curve. There are features in LCB that I wish were
backported to LCS. I appreciate the team's reticence to make syntax
changes to the core xtalk language, but even as a long-time C
programmer,
put tHexNumber converted from base 16 into tDecimalNumber
seems so much more readable than
put format("%02x", tHexNumber) into tDecimalNumber
I wouldn't say we have a 'reticence' to make syntax changes but it
requires
a great deal more care than in LCB for several reasons:
- The current implementation of LCS has no notion of versioning for
its
syntax or semantics - so every change to syntax / addition has to
be done
in a way which will not break user scripts.
- All the syntax in the engine is done using hand-coded parsing - it
is very
easy to introduce unintended ambiguities and syntactic forms which
we did
not intend.
- It is quite labour intensive to add / change syntax which means
experimenting
with it (which you need to do to get it 'just right') is hugely
costly.
In contrast, all of LCB's syntax (beyond the core control structures and
definiton
structures) is defined in LCB itself, and binds direct to handlers which
implement
that syntax (in contrast, in LCS, you have to write C++ code both to
parse a piece
of syntax, and to dispatch it to the implementation). For example, the
syntax you
mention above is defined like this:
syntax BaseConvert is left binary operator with conversion precedence
<Operand: Expression> "converted" "from" "base" <Source: Expression>
"to" "base" <Target: Expression>
begin
MCMathEvalConvertBase(Operand, Source, Target, output)
end syntax
With 'MCMathEvalConvertBase' being a (foreign) handler implemented in
C++ which performs
the action of the syntax.
The main limitation with LCB's syntax right now is that it has to be
compiled into
a parser spec ahead of time - i.e. at creation of the lc-compile tool -
but even with
that restriction, 'playing' with syntax is possible by just a tweak to a
code file and a click of
a button (albeit in a native code IDE), rather than spending many hours
hand modifying
some rather old (and in some places very complex) C++ code.
Of course, one valid retort here would be - then why don't you just make
it easier to
do this by changing how the engine works in this regard? And the simple
answer is that
we are - in order to do that we need an architecture and method of doing
so, and LCB is
that architecture.
Warmest Regards,
Mark.
--
Mark Waddingham ~ m...@livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps
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