justfile grammar
================
Justfiles are processed by a mildly context-sensitive tokenizer
and a recursive descent parser. The grammar is LL(k), for an
unknown but hopefully reasonable value of k.
tokens
------
```
BACKTICK = `[^`\n\r]*`
COMMENT = #([^!].*)?$
DEDENT = emitted when indentation decreases
EOF = emitted at the end of the file
INDENT = emitted when indentation increases
LINE = emitted before a recipe line
NAME = [a-zA-Z_][a-zA-Z0-9_-]*
NEWLINE = \n|\r\n
RAW_STRING = '[^'\r\n]*'
STRING = "[^"]*" # also processes \n \r \t \" \\ escapes
TEXT = recipe text, only matches in a recipe body
```
grammar syntax
--------------
```
| alternation
() grouping
_? option (0 or 1 times)
_* repetition (0 or more times)
_+ repetition (1 or more times)
```
grammar
-------
```
justfile : item* EOF
item : recipe
| alias
| assignment
| export
| setting
| eol
eol : NEWLINE
| COMMENT NEWLINE
alias : 'alias' NAME ':=' NAME
assignment : NAME ':=' expression eol
export : 'export' assignment
setting : 'set' 'shell' ':=' '[' string (',' string)* ','? ']'
expression : value '+' expression
| value
value : NAME '(' sequence? ')'
| STRING
| RAW_STRING
| BACKTICK
| NAME
| '(' expression ')'
string : STRING
| RAW_STRING
sequence : expression ',' sequence
| expression ','?
recipe : '@'? NAME parameter* variadic? ':' dependency* body?
parameter : NAME
| NAME '=' value
variadic : '*' parameter
| '+' parameter
dependency : NAME
| '(' NAME expression* ')
body : INDENT line+ DEDENT
interpolation : '{{' expression '}}'
```