taskwarrior/doc/misc/parser/README
Paul Beckingham 235fb9f054 Command Line Grammar
- Updated documentation.
2013-07-22 20:31:09 -04:00

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The main focus of the 2.4.0 release is a new command line parser that has more
capabilities with fewer quirks and bugs.
Improvements needed:
- Assorted quoting issues. If this command is issued, then the quoting should
be obeyed:
task add one project:'Bob\'s Project'
task add "one 'two' three"
task add 'one "two" three'
task add 'one \'two\' three'
task add "one \"two\" three"
- The process of splitting and rejoining tokens causes this kind of problem:
"one (two) three" --> "one ( two) three"
- Any formatting in the input that makes it past the shell should be preserved.
- The '--' token should faithfully cause no further parsing - lexing only.
- The ability to perform simple math:
task add one due:eoy wait:due-2wks scheduled:wait-1wk
When processed left to right, this command has referential integrity.
- An attribute value must be a single argument, but can be presented in several
equivalent ways:
wait:due-2wks
wait:'due-2wks'
wait:"due-2wks'
wait:"due -2wks'
wait:"due - 2wks'
wait:due\ -\ 2wks
Grammar:
To achieve the above, a formal grammar will be developed, otherwise a hand-
crafted parser is going to be unmaintainable. See the grammar.txt file for the
formal definition.
This grammar.txt will be embedded into task as a single-string document, then
itself parsed and used. This has several advantages:
- It allows the grammar to be discussed in its purest form, with an
authoritative document as a definition.
- It allows the grammar to be tweaked at a high level without code changes.
- It allows a developer to experiment with grammar.
Expressions:
The expression evaluator will be capable of applying any supported filter.
The expression evaluator will also be capable of evaluating fragments of output
from the parser, yielding a single value. As an example, the command line:
task add one due:eoy wait:due-2wks
Is to be parsed as:
raw | add one due:eoy wait:due-2wks
type | command string attr attr
subtype | read
attr | desc due wait
value | eval 'eoy' eval 'due-2wks'
The eval needs of this command are:
'eoy' == date literal
'due-2wks' == <dom> - <duration>