2.1 Why does the syntax change?

Often, syntax changes are made to make the input simpler to both read and write, but occasionally the changes are made to accommodate new features or enhancements to existing functions.

To illustrate this here is a real example:

All \paper and \layout property names were supposed to be written in the form first-second-third. However, in LilyPond version 2.11.60, it was noticed that the printallheaders property did not follow this convention. Should this property be left alone (confusing new users with an inconsistent format)? Or should it be changed (annoying old users with existing LilyPond input files)?

The decision was made to change the name of the property to print-all-headers, and by using the convert-ly command the old users had a way to automatically update their existing input files.

However, the convert-ly command cannot always be used to manage all syntax changes. In versions of LilyPond before 2.4.2, accents and non-English characters were entered using standard LaTeX notation. For example the French word for ‘Christmas’ was entered as No\"el. But in LilyPond 2.6 onwards, the special ë must be entered directly as a UTF-8 character. The convert-ly command cannot change LaTeX special characters into UTF-8 characters, so older LilyPond input files have to edited manually.

The conversion rules of the convert-ly command work using text pattern-matching and replacement (rather than ‘understanding’ the context of what it is changing within a given input file). This has several consequences:

• The reliability of the conversion depends on the quality of each applied rule set and on the complexity of the respective change. Sometimes conversions may require additional, manual fixes, so the original input files should be kept for comparison just in case.
• Only conversions to newer syntax changes are possible: there are no rule sets to go back to older versions of LilyPond. So the input file should only be upgraded when older versions of LilyPond are no longer being maintained. Again, the original input files should be kept just in case; perhaps using version control systems (i.e. Git) to help with maintaining multiple versions of your input files.
• LilyPond is quite robust when processing ‘creatively’ placed or omitted whitespace, but the rules used by convert-ly often make some stylistic assumptions. Therefore following the input style as used in the LilyPond manuals is advised for painless upgrades, particularly as the examples in the manuals themselves are all upgraded using the convert-ly command.

This document was generated by gub on July 13, 2020 using texi2html 1.82.

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