New: Expression blocks in Calcpad

[Proektsoftbg]

Dear friends,

I added the next big feature in Calcpad - expression blocks. You use them to embed a short algorithmic procedures with local variables in function definitions, inline loops and other expressions. There are two types of expression blocks: $block{expressions} and $inline{expressions}. The difference is only in the way they are rendered - multiline of inline. The expressions are separated by semicolons ";". Of course, you can write everything in one line of code, but you can also split it into several lines for readability by using line continuation symbol " _". If your line finishes with ";" and "}" you can skip adding " _".

Here is an example for two functions:

1. quadRoots returns a two-element vector with the roots of quadratic equations defined by three coefficients a, b, c.
2. fib is a functions that computes the n-th Fibonacci number.

'Multiline code block - quadratic equation roots
quadRoots(a; b; c) = _
$block{
    D = b^2 - 4*a*c; 
    x_1 = (-b - sqrt(D))/(2*a); 
    x_2 = (-b + sqrt(D))/(2*a); 
    [x_1; x_2]; 
}
quadRoots(2; 3; -5)
'Inline code block - quadratic equation roots
quadRoots(a; b; c) = $inline{D = b^2 - 4*a*c; x_1 = (-b - sqrt(D))/(2*a); x_2 = (-b + sqrt(D))/(2*a); [x_1; x_2]}
quadRoots(2; 3; -5)
'Iterative code block - Fibonacci numbers
fib(n) = if(n ≡ 1; 1; $block{a = 0; b = 1; $repeat{c = a + b; a = b; b = c @ k = 1 : n - 1}})
[fib(2); fib(3); fib(4); fib(5); 
fib(6); fib(7); fib(8); fib(9)]

[sononicola]

Hi Ned
If I understood correctly: block$s are basically macro$s that can return some values (as a vector) and with a local scope (Like functions in Python, for example) ?

Are there any disadvantages of just start using new block$s instead of old macro$s?

---

Just for reference, this is the Python equivalent:

[Proektsoftbg]

Hi! Not at all. They are completely different and have nothing in common.
Macros just preprocess the code and does nothing than text rewriting to produces the actually code to be executed. This is even before the actual calculations have started.

$Block and $Inline operate inside expressions during calculations. They are of the same family as $Integral, $Sum, $Product and $Repeat. The difference is that the dollar symbol is in front while for macros it is behind the name.

[Proektsoftbg]

Yes, $block inside function will be the equivalent of this Python multiline function.
Macros ar equivalent to C macros:
https://www.geeksforgeeks.org/c/macros-and-its-types-in-c-cpp/
They are just text rewriting.

[sononicola]

@Proektsoftbg Thankyou I understand better now. I will definitely start using $block since I'm used to Python syntax and I like how I can choose what returning and what must remain a local variable

[javila]

Hi, @Proektsoftbg!

I was playing around with the new $Block feature and I was getting some weird responses while trying to implement a function. Then I decided to try your example and I found out that the block variables are not really local (and that was the reason I was getting unexpected results too).

[Proektsoftbg]

Hi! I think I fixed it. You can use global variables in expression blocks but locally created variables are not visible outside and do not affect global variables' values. Please note that $repeat{} still creates global variables as before. I did not change that for compatibility, otherwise many worksheets will stop working. If you do not want it to affect global variables, just put it in a block as in the Fibonacci example:
https://github.com/Proektsoftbg/Calcpad/blob/main/Examples/Demos/Multiline%20functions/Fibonacci%20numbers.cpd

$repeat{} is just like the multiline loops #repeat, #for and #while which also create global variables inside. Only $block{} and $inline{} can create local variables.

I updated the source code for now. Please, give it a try and if everything is OK, next week I will release it next week as v.7.5.1.

[javila]

Hi, @Proektsoftbg!

It seems the variables are local now. I'll do some extra tests anyway. I'm still trying to figure out the best way to write some functions (like the ones I mentioned here)...

[javila]

Hi, @Proektsoftbg!

I did some extra tests and discovered another problem...

I think the local variables may be really fixed. I learnt that a nested block can use its "parent" block variables but it cannot use its "sibling" block ones. I think this is good.

Then I decided to try to change the test a bit to include some vectors inside blocks. The results were completely wrong:

Finally I decided to investigate the problem and I found out that switch functions doesn't work well with vectors while nested if ones does:

Then I could switch the switch (pun intended) function to nested if ones and the results were as expected:

So... Using nested iffunctions I could finally attempt to solve my problem (of course, I wasn't expecting that the "complex" function could be rendered prettily - I didn't plan to show it at all, though):

Note: vectors and vectorized operations are not being correctly "rendered" inside block!

[javila]

Just a complement to my previous answer... I suspect there is something wrong with vectors/matrices created inside blocks. Maybe that's why they aren't being rendered as expected.

[Proektsoftbg]

Hi! Thank you for your feedback.

Actually vectors and matrices are not rendered at all. Like normal variables, their content is not substituted. What you see inside the block is the square bracket operator [] that creates them and that you normally see outside blocks.

What actually happen is that in your case, the function gets too long in this way, does not fit in the line and elements gets displaced.
Currently, I do not know how to solve it, but I will do some more research. But about creating and assigning to vector/matrix elements results look really strange. I will check them out.

It is also interesting about switch() function. Maybe it has always been like that and no one has noticed it before. I will make it now compatible with vectors and matrices.

[Proektsoftbg]

Hi!

I made quite and advancement in fixing these things.

Please, check the latest commit.

[Proektsoftbg]

Hi! Yes _ is for line continuation and it was several versions ago, but now maybe a bug appeared. I will check it out.

[Proektsoftbg]

Ready! It is fixed now.

[javila]

Hi, @Proektsoftbg!

That's wonderful! It's working again.

I have another suggestion, though... 😁Since (, { e ; are already making _ unnecessary in the end of a line, why not making | work the same way? It would would make matrices rows typing even easier/nicer...

[Proektsoftbg]

That is a great idea! I wonder why it didn't occur to me. Actually, there is no reason to add all delimiter chars and opening brackets. How about this:

[javila]

Perfect, @Proektsoftbg!

[Asg1109]

Can't use #for loop inside $block

[Proektsoftbg]

No, you can't. You must use its inline equivalent: $Repeat{...; ...; ... @ i = 1 : n}. But but now you can put multiple expressions inside, just like in a $Block. Check this Fibonacci numbers example:
https://github.com/Proektsoftbg/Calcpad/blob/main/Examples/Demos/Multiline%20functions/Fibonacci%20numbers.cpd

Why is that?. Calcpad has three different types of objects that operate on different levels and are processed at different stages:

1. Modules and macros: #include, #local, #global and #def. They are preprocessed by a text rewriting engine that composes the actual (unwrapped) code. This is performed by the Macro Parser module. Nothing is calculated and this stage. This is the outermost layer that wraps the other.

2. Worksheet level keywords/blocks like: #show, #hide, #val, #equ and also #for, #while, #repeat, #if, #else, #end if, and any other starting with '#' They are located in an outer layer and are processed before inline objects like expressions and functions. You can put multiple expressions in a worksheet level object but you cannot put a worksheet level object inside an inline one even with a $block {}. Worksheet level objects can affect the content of the report, to determine whether the expressions inside will execute or show and how they will look. This layer is processed by the Expression Parser module. It wraps the inline objects layer.

3. "Inline" objects like math expressions, functions, $...{} commands and blocks. They are located in an inner layer and processed after the worksheet level elements. $block{} and $inline{} operate in this layer. They are used to pack other inline expressions inside an outer one. So, you can put there only elements from the same layer. All inline elements are processed at the final "calculation" step by the Math Parser module. Plots commands are sent to Plot Parser.

When I have some more time, I will draw some schemes and provide more detailed explanations about this object hierarchy and how Calcpad works internally.

[javila]

I really appreciated this explanation. This helps a lot to understand how Calcpad works "under the hood"...

[Asg1109]

$repeat worked for me

[andrewjrcass]

hi
I'm having a weird behavior on calcpad's block.
Can someone help me to understand it. Thanks

[javila]

Hi, @andrewjrcass!

I suppose it may work if you change your code to:

$Plot{f(xx) & x.1|y1 & x.2|y2 @ xx = -3 : 3 }

[andrewjrcass]

Now it works

[Asg1109]

how to wrap/split large equations in $block{}. tried using #split and #wrap command.

[Proektsoftbg]

Hi! Put it in a div with class .wrap and add max-width css. For example:

'<style>.wrap .block{max-width:200pt;}</style>
'<div class="wrap">
f(x) = $Block{
    a = (sin(x) + cos(x))/2 + _
    (sin(2*x) + cos(2*x))/2 + _
    (sin(3*x) + cos(3*x))/2 _
 }
'</div>

If you want this to apply only for internal block inside another block, use this instead:

'<style>.wrap .block .block{max-width:200pt;}</style>

Or simply assign different terms to local variables first and then sum the variables.