choice function
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eaafdaa777
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@ -1,6 +1,6 @@
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use crate::parser::Parser;
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use crate::parser::{ParseResult, Parser};
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pub fn choice<P1, P2, I, O, E>(parser1: P1, parser2: P2) -> impl Parser<I, O, E>
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pub fn choice2<P1, P2, I, O, E>(parser1: P1, parser2: P2) -> impl Parser<I, O, E>
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where
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P1: Parser<I, O, E>,
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P2: Parser<I, O, E>,
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@ -12,6 +12,43 @@ where
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}
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}
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pub fn choice<C, I, O, E>(choices: C) -> impl Parser<I, O, E>
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where
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C: Choice<I, O, E>,
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I: Clone,
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{
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move |input| choices.parse(input)
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}
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pub trait Choice<I: Clone, O, E> {
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fn parse(&self, input: I) -> ParseResult<I, O, E>;
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}
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impl<I, O, E, P1, P2> Choice<I, O, E> for (P1, P2)
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where
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P1: Parser<I, O, E>,
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P2: Parser<I, O, E>,
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I: Clone,
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{
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fn parse(&self, input: I) -> ParseResult<I, O, E> {
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let parser1 = &self.0;
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let parser2 = &self.1;
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//TODO need a more principled way to return an error when no choices work
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let mut err = None;
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for parser in [parser1 as &dyn Parser<I, O, E>, parser2].iter() {
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match parser.parse(input.clone()) {
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Ok(result) => return Ok(result),
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Err(e) => {
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err = Some(e);
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}
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}
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}
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Err(err.unwrap())
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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@ -20,7 +57,7 @@ mod tests {
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#[test]
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fn test_choice() {
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let p = choice(literal("gnostika").to(1), one_or_more(literal(" ")).to(2));
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let p = choice2(literal("gnostika").to(1), one_or_more(literal(" ")).to(2));
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assert_eq!(p.parse("gnostika twentynine"), Ok((1, " twentynine")));
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}
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}
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@ -45,7 +45,7 @@ mod tests {
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let json_true = literal("true").to(JsonValue::Bool(true));
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let json_false = literal("false").to(JsonValue::Bool(false));
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let json_value = choice(json_null, choice(json_true, json_false));
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let json_value = choice((json_null, choice((json_true, json_false))));
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assert_eq!(json_value.parse("true"), Ok((JsonValue::Bool(true), "")));
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}
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