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74 lines
2.4 KiB
74 lines
2.4 KiB
6 years ago
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// Package participle constructs parsers from definitions in struct tags and parses directly into
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// those structs. The approach is philosophically similar to how other marshallers work in Go,
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// "unmarshalling" an instance of a grammar into a struct.
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//
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// The supported annotation syntax is:
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//
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// - `@<expr>` Capture expression into the field.
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// - `@@` Recursively capture using the fields own type.
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// - `<identifier>` Match named lexer token.
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// - `( ... )` Group.
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// - `"..."` Match the literal (note that the lexer must emit tokens matching this literal exactly).
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// - `"...":<identifier>` Match the literal, specifying the exact lexer token type to match.
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// - `<expr> <expr> ...` Match expressions.
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// - `<expr> | <expr>` Match one of the alternatives.
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//
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// The following modifiers can be used after any expression:
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//
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// - `*` Expression can match zero or more times.
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// - `+` Expression must match one or more times.
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// - `?` Expression can match zero or once.
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// - `!` Require a non-empty match (this is useful with a sequence of optional matches eg. `("a"? "b"? "c"?)!`).
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//
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// Supported but deprecated:
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//
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// - `{ ... }` Match 0 or more times (**DEPRECATED** - prefer `( ... )*`).
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// - `[ ... ]` Optional (**DEPRECATED** - prefer `( ... )?`).
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//
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// Here's an example of an EBNF grammar.
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//
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// type Group struct {
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// Expression *Expression `"(" @@ ")"`
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// }
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//
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// type Option struct {
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// Expression *Expression `"[" @@ "]"`
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// }
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//
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// type Repetition struct {
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// Expression *Expression `"{" @@ "}"`
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// }
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//
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// type Literal struct {
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// Start string `@String` // lexer.Lexer token "String"
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// End string `("…" @String)?`
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// }
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//
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// type Term struct {
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// Name string ` @Ident`
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// Literal *Literal `| @@`
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// Group *Group `| @@`
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// Option *Option `| @@`
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// Repetition *Repetition `| @@`
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// }
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//
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// type Sequence struct {
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// Terms []*Term `@@+`
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// }
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//
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// type Expression struct {
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// Alternatives []*Sequence `@@ ("|" @@)*`
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// }
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//
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// type Expressions []*Expression
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//
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// type Production struct {
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// Name string `@Ident "="`
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// Expressions Expressions `@@+ "."`
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// }
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//
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// type EBNF struct {
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// Productions []*Production `@@*`
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// }
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package participle
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