Template language changes

[un_pogaz]

Nothing, that'll teach me not to read the whole doc

Spoiler:

Cool, but why merge the value and type into 1 element?
Wouldn't it be easier to separate them into 2 like date_arithmetic(date, value, type, fmt*)
is much more understandable, right?

EDIT: crap, I thought that as the function was not yet officially implemented, I thought we had time to "debate" it.
But the question remains.

[chaley]

Originally Posted by un_pogaz

Nothing, that'll teach me not to read the whole doc

For completeness, the reason for the string is that you can specify several operations in one call, for example adding 3 days, 12 hours, and 30 minutes (3d12h30m).

[ownedbycats]

Originally Posted by chaley

And yes, the 'months' specifier is missing, because the number of days in a month depend on both the source date month and year. This is also why a year is fixed at 365 days.

Curious: is there any handling for leap years?

[chaley]

Originally Posted by ownedbycats

Curious: is there any handling for leap years?

Nope.

[ownedbycats]

I hope it doesn't break if a date is set to February 29, 2020. I'm testing it myself but still working out how the syntax works.

[chaley]

Originally Posted by ownedbycats

I hope it doesn't break if a date is set to February 29, 2020. I'm testing it myself but still working out how the syntax works.

It won't break if the date ends up being on 29 Feb of a leap year. For example, 28 Feb 2020 + (1 day) will produce 29 Feb 2020. The date 28 Feb 2021 + (1 day) will produce 1 Mar 2021

By not supporting leap year I mean that with the exception of years, no calculation requires knowledge of whether 29 Feb (EDIT: or any other day of the month) matters. That is why there is no "month" calculation specifier, because the calculation can change when going over a leap February (EDIT: or if the current day doesn't exist in the target month). The problem is finessed for "years" by defining a year as 365 days, which given a valid date can never generate an invalid date, but the result might be a day short.

The syntax is straightforward: pairs of (numbers followed by a letter). The order is not important. Examples:

• -10w: subtract 10 weeks.
• 3d-1y: add 3 days and subtract 1 year.
• -1y3d-10w: subtract one year, add 3 days, then subtract 10 weeks.

[chaley]

Bug in calibre versions V5.23 - V5.28: Composite column templates that use Template Program Mode and reference other composite columns can sometimes generate list index error exceptions. Using General Program Mode instead of Template Program Mode avoids the error.

EDIT: Fixed in V5.29

[chaley]

Bug in calibre versions 5.13 - 5.29: the assign() function wouldn't parse. The fix will be in the next calibre release.

Thanks to David Tardon for finding and fixing this bug.

[ownedbycats]

You have a different kitty!

[theducks]

Originally Posted by ownedbycats

You have a different kitty!

I wonder how many MR members have cats in their Avatars?
(I know a whole lot have feline helpers at home)

[chaley]

Originally Posted by ownedbycats

You have a different kitty!

Originally Posted by theducks

I wonder how many MR members have cats in their Avatars?
(I know a whole lot have feline helpers at home)

We have three, 2 ginger brothers and one calico. She was my previous avatar and is still feral. I must use welder's leather arm gloves to pick her up. One brother (the current avatar) insists on helping with everything and everyone; plumbers in particular appreciate him jumping on their backs to inspect their work. The other brother is nervous and shy but is the most skillful at hunting down cat treats.

[chaley]

31 October 2021 (In calibre 5.31.1)

• Bug fix: the binary arithmetic operators (+ - * /) failed if either value was undefined e.g., if $$#myint doesn't have a value for the book. The fix: make them work like the comparison operators: assume undefined is zero.

[chaley]

10 November 2021 (In calibre source)

• Add the function current_virtual_library_name(). The documentation:
  

  Return the name of the current virtual library if there is one, otherwise the empty string. Library name case is preserved. Example:
  

  program: current_virtual_library_name()

  This function can be used only in the GUI.

[chaley]

11 November 2021 (in calibre source)

• Fix: fix failure to inline the functions first_non_empty() and test().
• New: inline the strcat() function

[chaley]

27 March 2022 (In calibre version 5.40)

• The ability to define local functions. For example, the following example computes an approximate duration in years, months, days from a number of days. It uses the defined local function to_plural() to format the numbers for output.
  

  program:
  	days = 2112;
  	years = floor(days/360);
  	months = floor(mod(days, 360)/30);
  	days = days - ((years*360) + (months * 30));
  
  	def to_plural(v, str):
  		if v == 0 then return '' fi;
  		return v & ' ' & (if v == 1 then str else str & 's' fi) & ' '
  	fed;
  
  	to_plural(years, 'year') & to_plural(months, 'month') & to_plural(days, 'day')

  Notes:
  • The grammar for defining a function is
    

    function ::= 'def' function_name '(' argument_expr [',' argument_expr]* ')' ':' 
                  expression_list 'fed'
    argument_expr ::= identifier | identifier '=' expression

  • Functions must be defined before they are used.
  • The outer scope local variables are not visible inside a function.
  • The parameters in the definition can have default values.
  • You can call a function with fewer arguments than defined parameters. Parameters matched to 'missing' arguments are given their default value or the empty string if there isn't a default value.
• A 'concatenate strings' operator '&'. The expression
  

  'aaa' & 'bbb' & 'ccc'

  is equivalent to
  

  strcat('aaa', 'bbb', 'ccc')