From 6639605b395ceb1355c95e06ff0e1470adc54101 Mon Sep 17 00:00:00 2001
From: Akshay Nair <phenax5@gmail.com>
Date: Fri, 7 Jan 2022 18:13:40 +0530
Subject: refactor: simplifies quantifier logic + moves stuff around

---
 src/parser/utils.ts | 162 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 162 insertions(+)
 create mode 100644 src/parser/utils.ts

(limited to 'src/parser/utils.ts')

diff --git a/src/parser/utils.ts b/src/parser/utils.ts
new file mode 100644
index 0000000..00b50f8
--- /dev/null
+++ b/src/parser/utils.ts
@@ -0,0 +1,162 @@
+import { constant, flow, pipe } from 'fp-ts/function'
+import {
+  Either,
+  left,
+  right,
+  map,
+  chain,
+  orElse,
+  fold,
+  orElseW,
+} from 'fp-ts/Either'
+import { none, some, Option } from 'fp-ts/Option'
+import { mapFst, mapSnd, snd } from 'fp-ts/Tuple'
+import { eq } from '../utils'
+
+export type char = string
+
+export type ParserState<T> = [T, string]
+export type ParserError = [string, string]
+export type ParserResult<T> = Either<ParserError, ParserState<T>>
+export type Parser<T> = (input: string) => ParserResult<T>
+
+export const constP =
+  <T>(v: T): Parser<T> =>
+  (inp: string) =>
+    right([v, inp])
+
+export const many0 = <T>(parser: Parser<T>): Parser<Array<T>> =>
+  flow(
+    parser,
+    chain(([a, nextInput]) =>
+      pipe(nextInput, many0(parser), map(mapFst((ls) => [a, ...ls])))
+    ),
+    orElse(
+      flow(
+        mapFst((_) => [] as T[]),
+        right
+      )
+    )
+  )
+
+export const many1 = <T>(parser: Parser<T>): Parser<Array<T>> =>
+  flow(
+    many0(parser),
+    chain(([res, inp]) =>
+      res.length > 0
+        ? right([res, inp])
+        : left([`many1 failed to parse at ${inp}`, inp])
+    )
+  )
+
+const recoverInput =
+  <T>(p: Parser<T>): Parser<T> =>
+  (input: string) =>
+    pipe(
+      input,
+      p,
+      orElseW(
+        flow(
+          mapSnd((_) => input),
+          left
+        )
+      )
+    )
+
+export const prefixed = <T>(a: Parser<any>, b: Parser<T>): Parser<T> =>
+  recoverInput(flow(a, chain(flow(snd, b))))
+
+export const suffixed = <T>(a: Parser<T>, b: Parser<any>): Parser<T> =>
+  recoverInput(
+    flow(
+      a,
+      chain(([out, inp]) => pipe(inp, b, map(mapFst((_) => out))))
+    )
+  )
+
+export const delimited = <T>(
+  p: Parser<any>,
+  a: Parser<T>,
+  s: Parser<any>
+): Parser<T> => suffixed(prefixed(p, a), s)
+
+export const satifyChar =
+  (f: (c: char) => boolean): Parser<char> =>
+  (input: string) => {
+    const c = input.charAt(0)
+    if (f(c)) return right([c, input.slice(1)])
+    return left([`Expected to satisfy ${f}, got "${c}"`, input])
+  }
+
+export const digit = satifyChar((c) => /^[0-9]$/g.test(c))
+
+export const integer: Parser<number> = flow(
+  many1(digit),
+  map(mapFst((ds) => parseInt(ds.join(''), 10)))
+)
+
+export const or = <T>(parsers: Parser<T>[]): Parser<T> => {
+  const run = ([p, ...ps]: Parser<T>[]) =>
+    flow(
+      p,
+      orElse(([_, inp]) => or(ps)(inp))
+    )
+
+  return parsers.length > 0
+    ? run(parsers)
+    : (inp: string) => left(['unable to match', inp])
+}
+
+export const matchChar = (ch: char): Parser<char> => satifyChar(eq(ch))
+
+export const space = matchChar(' ')
+export const newline = matchChar('\n')
+export const tab = matchChar('\t')
+
+export const whitespace = or([space, newline, tab])
+export const whitespaces0 = many0(whitespace)
+
+export const matchString =
+  (s: string): Parser<string> =>
+  (input: string) =>
+    input.slice(0, s.length) === s
+      ? right([s, input.slice(s.length)])
+      : left([`Expected ${s} but got ${input.slice(0, 1)}`, input])
+
+export const symbol = (s: string): Parser<string> =>
+  delimited(whitespaces0, matchString(s), whitespaces0)
+
+export const mapTo = <I, R>(p: Parser<I>, f: (p: I) => R): Parser<R> =>
+  flow(p, map(mapFst(f)))
+
+export const andThen =
+  <I, R>(f: (p: I) => Parser<R>) =>
+  (p: Parser<I>): Parser<R> =>
+    flow(
+      p,
+      chain(([v, inp]) => f(v)(inp))
+    )
+
+export const optional = <T>(p: Parser<T>): Parser<Option<T>> =>
+  flow(
+    p,
+    fold(
+      flow(
+        mapFst((_) => none),
+        right
+      ),
+      flow(mapFst(some), right)
+    )
+  )
+
+export const pair = <A, B>(a: Parser<A>, b: Parser<B>): Parser<[A, B]> =>
+  pipe(
+    a,
+    andThen((ra) => mapTo(b, (rb) => [ra, rb]))
+  )
+
+export const tuple3 = <A, B, C>(
+  a: Parser<A>,
+  b: Parser<B>,
+  c: Parser<C>
+): Parser<[A, B, C]> => mapTo(pair(pair(a, b), c), ([[a, b], c]) => [a, b, c])
-- 
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