just/GRAMMAR.md

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justfile grammar
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================
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Justfiles are processed by a mildly context-sensitive tokenizer
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and a recursive descent parser. The grammar is mostly LL(1),
although an extra token of lookahead is used to distinguish between
export assignments and recipes with parameters.
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tokens
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------
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```
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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)
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```
grammar
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-------
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```
justfile : item* EOF
item : recipe
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| alias
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| assignment
| export
| eol
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eol : NEWLINE
| COMMENT NEWLINE
assignment : NAME '=' expression eol
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alias : 'alias' NAME '=' NAME
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export : 'export' assignment
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expression : value '+' expression
| value
value : NAME '(' arguments? ')'
| STRING
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| RAW_STRING
| BACKTICK
| NAME
| '(' expression ')'
arguments : expression ',' arguments
| expression ','?
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recipe : '@'? NAME parameter* ('+' parameter)? ':' dependencies? body?
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parameter : NAME
| NAME '=' value
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dependencies : NAME+
body : INDENT line+ DEDENT
line : LINE (TEXT | interpolation)+ NEWLINE
| NEWLINE
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interpolation : '{{' expression '}}'
```