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Document rule precedence + slight clarification for error recovery

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Robin Jadoul 2017-01-30 20:57:18 +01:00
parent 25e346b8cd
commit 9136756c04
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README.md
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@ -104,7 +104,7 @@ Furthermore, Parsodus uses a couple of key-value associations, including
- start: a variable to use as the start symbol
- grammar: a list of rules (see below)
A grammar rule is a variable followed by `::=` followed by a `|`-separated list of rule tails ended with a semicolon. A rule tail is a list of variables and terminals followed by an optional rule name of the form `[name]`.
A grammar rule is a variable followed by `::=` followed by a `|`-separated list of rule tails ended with a semicolon. A rule tail is a list of variables and terminals followed by an optional rule name of the form `[name]`. These annotations can additionally contain a specific precedence for this rule (a common example for this is the unary minus in mathematical expressions) in the form of a precedence specifier (`left`, `right` or `nonassoc`) followed by a non-negative integer. This integer specifies the precedence level for that rule (higher means higher precedence). Otherwise, the precedence for a rule is determined by the precedence of its last terminal. The lowest precedence in the *precedence* section of the file has precedence level 0.
parser: lalr(1)
terminals:
@ -130,6 +130,8 @@ In general, there should be some way to run the parser, along with user defined
If you provide a rule with `<error>` somewhere inside the body, this can be used to recover from errors. The generated parser will discard states until it encounters somewhere it can use such a rule. Afterwards, it will start discarding tokens until it can proceed in parsing. If it's impossible to recover from the error (cannot find a recovery rule or cannot find a synchronizing token before EOF), there will generally be an error (depending on the backend). Usually, some sort of reporting mechanism should also be in place by the generated parser.
`<error>` should never appear as the head of a grammar rule.
### Bash completion
A file that provides bash completion is also provided for your convenience, to use it, do: