Function set

Return a parser that takes a key and a value. The parser consumes no input and always succeeds, and returns null as the result. It also returns a captures object with that key-value pair set. This is useful when you need to inject a key-value pair into captures for a seq.

For example, here is a Markdown heading parser.

export const headingParser: Parser<Heading> = seqC(
  capture(count(char("#")), "level"),
  spaces,
  capture(many1Till(or(char("\n"), eof)), "content")
);
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This parser returns

{
  level: number,
  content: string
}
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but the type of heading is actually

type Heading = {
  type: "heading";
  level: number;
  content: string;
};
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The type key is missing. You can use set to inject the type key-value pair into captures:

export const headingParser: Parser<Heading> = seqC(
  set("type", "heading"),
  capture(count(char("#")), "level"),
  spaces,
  capture(many1Till(or(char("\n"), eof)), "content")
);
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