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import gleam/string
import gleam/list
import gleam/function
import gleam/pair
import ext/resultx
import ext/intx
// Heavily inspired by https://fsharpforfunandprofit.com/posts/understanding-parser-combinators/
pub type ParseResult(a) =
Result(#(a, String), String)
pub opaque type Parser(a) {
Parser(parser: fn(String) -> ParseResult(a))
}
pub fn run(parser: Parser(a), on input: String) -> ParseResult(a) {
assert Parser(function) = parser
function(input)
}
pub fn any_grapheme() -> Parser(String) {
let inner = fn(input) {
case string.pop_grapheme(input) {
Ok(#(first, rest)) -> Ok(#(first, rest))
_ -> Error("Error!")
}
}
Parser(inner)
}
pub fn grapheme(expected: String) -> Parser(String) {
let inner = fn(input) {
case string.pop_grapheme(input) {
Ok(#(first, rest)) if first == expected -> Ok(#(expected, rest))
_ -> Error("Error!")
}
}
Parser(inner)
}
pub fn and_then(parser1: Parser(a), parser2: Parser(b)) -> Parser(#(a, b)) {
let inner = fn(input) {
let result1 = run(parser1, on: input)
case result1 {
Error(err) -> Error(err)
Ok(#(value1, remaining1)) -> {
let result2 = run(parser2, on: remaining1)
case result2 {
Error(err) -> Error(err)
Ok(#(value2, remaining2)) -> {
let new_value = #(value1, value2)
Ok(#(new_value, remaining2))
}
}
}
}
}
Parser(inner)
}
pub fn then_skip(parser1: Parser(a), parser2: Parser(b)) -> Parser(a) {
parser1
|> and_then(parser2)
|> map(with: pair.first)
}
pub fn or_else(parser1: Parser(a), parser2: Parser(a)) -> Parser(a) {
let inner = fn(input) {
let result1 = run(parser1, on: input)
case result1 {
Ok(_result) -> result1
Error(_err) -> {
let result2 = run(parser2, on: input)
result2
}
}
}
Parser(inner)
}
pub fn choice(from parsers: List(Parser(a))) -> Parser(a) {
list.reduce(over: parsers, with: or_else)
|> resultx.force_unwrap
}
pub fn any_of(given graphemes: List(String)) -> Parser(String) {
graphemes
|> list.map(with: grapheme)
|> choice
}
pub fn lowercase() -> Parser(String) {
"abcdefghijklmnopqrstuvwxyz"
|> string.to_graphemes
|> any_of
}
pub fn digit() -> Parser(String) {
"0123456789"
|> string.to_graphemes
|> any_of
}
pub fn map(parser: Parser(a), with mapper: fn(a) -> b) -> Parser(b) {
let inner = fn(input) {
let result = run(parser, on: input)
case result {
Ok(#(value, remaining)) -> {
let new_value = mapper(value)
Ok(#(new_value, remaining))
}
Error(err) -> Error(err)
}
}
Parser(inner)
}
fn return(x: a) -> Parser(a) {
let inner = fn(input) { Ok(#(x, input)) }
Parser(inner)
}
fn apply(fp: Parser(fn(a) -> b), xp: Parser(a)) -> Parser(b) {
and_then(fp, xp)
|> map(fn(p) {
let #(f, x) = p
f(x)
})
}
fn lift2(f: fn(a, b) -> c) -> fn(Parser(a), Parser(b)) -> Parser(c) {
let inner = fn(xp, yp) {
let fc = function.curry2(f)
apply(apply(return(fc), xp), yp)
}
inner
}
pub fn sequence(of parsers: List(Parser(a))) -> Parser(List(a)) {
let cons_p = lift2(list.prepend)
case parsers {
[] -> return([])
[head, ..tail] -> cons_p(sequence(tail), head)
}
}
fn parse_zero_or_more(parser: Parser(a), input: String) -> #(List(a), String) {
let first_result = run(parser, on: input)
case first_result {
Error(_err) -> #([], input)
Ok(#(first_value, input_after_first_parse)) -> {
let #(subsequent_values, remaining_input) =
parse_zero_or_more(parser, input_after_first_parse)
let values = [first_value, ..subsequent_values]
#(values, remaining_input)
}
}
}
pub fn many(parser: Parser(a)) -> Parser(List(a)) {
let inner = fn(input) { Ok(parse_zero_or_more(parser, input)) }
Parser(inner)
}
pub fn many1(parser: Parser(a)) -> Parser(List(a)) {
let inner = fn(input) {
let first_result = run(parser, on: input)
case first_result {
Error(err) -> Error(err)
Ok(#(first_value, input_after_first_parse)) -> {
let #(subsequent_values, remaining_input) =
parse_zero_or_more(parser, input_after_first_parse)
let values = [first_value, ..subsequent_values]
Ok(#(values, remaining_input))
}
}
}
Parser(inner)
}
pub fn int() -> Parser(Int) {
digit()
|> many1
|> map(with: function.compose(string.concat, intx.force_parse))
}
pub fn all_remaining() -> Parser(String) {
any_grapheme()
|> many
|> map(with: string.concat)
}
|
