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import gleam/string
import gleam/list
import gleam/function
import gleam/pair
import gleam/result
import ext/intx
// Heavily inspired by https://fsharpforfunandprofit.com/posts/understanding-parser-combinators/
const eof: String = "end of input"
fn quot(grapheme: String) -> String {
"'" <> grapheme <> "'"
}
pub type ParseError {
InvalidInput(expected: String, found: String)
InvalidParser
}
type ParseResult(a) =
Result(#(a, String), ParseError)
pub opaque type Parser(a) {
Parser(function: fn(String) -> ParseResult(a))
}
fn run(parser: Parser(a), on input: String) -> ParseResult(a) {
parser.function(input)
}
pub fn parse_partial(
input: String,
with parser: Parser(a),
) -> Result(#(a, String), ParseError) {
run(parser, on: input)
}
pub fn parse_entire(
input: String,
with parser: Parser(a),
) -> Result(a, ParseError) {
case parse_partial(input, with: parser) {
Ok(#(value, "")) -> Ok(value)
Ok(#(_, rest)) -> Error(InvalidInput(expected: eof, found: rest))
Error(error) -> Error(error)
}
}
pub fn any_grapheme() -> Parser(String) {
Parser(fn(input) {
input
|> string.pop_grapheme
|> result.replace_error(InvalidInput(expected: "any grapheme", found: eof))
})
}
pub fn grapheme_literal(expected: String) -> Parser(String) {
Parser(fn(input) {
case run(any_grapheme(), on: input) {
Ok(#(value, _)) as ok if value == expected -> ok
Ok(#(value, _)) -> Error(InvalidInput(quot(expected), found: quot(value)))
Error(_) -> Error(InvalidInput(quot(expected), found: eof))
}
})
}
pub fn then(first: Parser(a), second: Parser(b)) -> Parser(#(a, b)) {
Parser(fn(input) {
use parsed1 <- result.then(run(first, on: input))
let #(value1, remaining1) = parsed1
use parsed2 <- result.then(run(second, on: remaining1))
let #(value2, remaining2) = parsed2
Ok(#(#(value1, value2), remaining2))
})
}
pub fn then_skip(first: Parser(a), second: Parser(b)) -> Parser(a) {
first
|> then(second)
|> map(with: pair.first)
}
pub fn then_third(two: Parser(#(a, b)), third: Parser(c)) -> Parser(#(a, b, c)) {
two
|> then(third)
|> map(with: fn(tuple) {
let #(#(p0, p1), p2) = tuple
#(p0, p1, p2)
})
}
pub fn or(first: Parser(a), else second: Parser(a)) -> Parser(a) {
Parser(fn(input) {
first
|> run(on: input)
|> result.or(run(second, on: input))
})
}
pub fn any(of parsers: List(Parser(a))) -> Parser(a) {
parsers
|> list.reduce(with: or)
|> result.unwrap(or: failing(with: InvalidParser))
}
pub fn digit() -> Parser(String) {
"0123456789"
|> string.to_graphemes
|> list.map(with: grapheme_literal)
|> any
// TODO: replace error
}
pub fn map(parser: Parser(a), with mapper: fn(a) -> b) -> Parser(b) {
Parser(fn(input) {
use parsed <- result.then(run(parser, on: input))
let #(value, remaining) = parsed
Ok(#(mapper(value), remaining))
})
}
pub fn map2(parser: Parser(#(a, b)), with mapper: fn(a, b) -> c) -> Parser(c) {
parser
|> map(with: fn(args) { mapper(args.0, args.1) })
}
pub fn map3(
parser: Parser(#(a, b, c)),
with mapper: fn(a, b, c) -> d,
) -> Parser(d) {
parser
|> map(with: fn(args) { mapper(args.0, args.1, args.2) })
}
fn succeeding(with value: a) -> Parser(a) {
Parser(fn(input) { Ok(#(value, input)) })
}
fn failing(with error: ParseError) -> Parser(a) {
Parser(fn(_) { Error(error) })
}
fn lift2(function: fn(a, b) -> c) -> fn(Parser(a), Parser(b)) -> Parser(c) {
fn(x_parser, y_parser) {
function
|> succeeding
|> then(x_parser)
|> then_third(y_parser)
|> map3(with: fn(f, x, y) { f(x, y) })
}
}
pub fn sequence(of parsers: List(Parser(a))) -> Parser(List(a)) {
let prepend_parser = lift2(fn(x, xs) { [x, ..xs] })
case parsers {
[] -> succeeding(with: [])
[head, ..tail] ->
tail
|> sequence
|> prepend_parser(head, _)
}
}
fn do_zero_or_more(input: String, with parser: Parser(a)) -> #(List(a), String) {
case run(parser, on: input) {
Ok(#(value, rest)) -> {
let #(previous, rest) = do_zero_or_more(rest, with: parser)
#([value, ..previous], rest)
}
Error(_) -> #([], input)
}
}
pub fn many(of parser: Parser(a)) -> Parser(List(a)) {
Parser(fn(input) { Ok(do_zero_or_more(input, with: parser)) })
}
pub fn many1(of parser: Parser(a)) -> Parser(List(a)) {
Parser(fn(input) {
use parsed <- result.then(run(parser, on: input))
let #(value, rest) = parsed
let #(previous, rest) = do_zero_or_more(rest, with: parser)
Ok(#([value, ..previous], rest))
})
}
pub fn int() -> Parser(Int) {
digit()
|> many1
|> map(with: function.compose(string.concat, intx.force_parse))
}
pub fn any_string() -> Parser(String) {
any_grapheme()
|> many
|> map(with: string.concat)
}
pub fn string_literal(expected: String) -> Parser(String) {
expected
|> string.to_graphemes()
|> list.map(with: grapheme_literal)
|> sequence
|> map(with: string.concat)
}
|
