From f129d1d6e8f03e586952d8c792c8e085ae7bca85 Mon Sep 17 00:00:00 2001
From: Akshay Nair <phenax5@gmail.com>
Date: Thu, 6 Jan 2022 21:08:12 +0530
Subject: feat: basic parser

---
 src/index.ts | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 55 insertions(+), 1 deletion(-)

(limited to 'src/index.ts')

diff --git a/src/index.ts b/src/index.ts
index 71455c6..a9b3409 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1 +1,55 @@
-export const x: number = 200
+import { flow, identity, pipe } from 'fp-ts/function'
+import { Either, left, right, map, chain, mapLeft, fold, orElse } from 'fp-ts/Either'
+
+type char = string
+
+type ParserResult<T> = [T, string]
+type ParserError = [string, string]
+type Parser<T> = (input: string) => Either<ParserError, ParserResult<T>>
+
+export const many0 = <T>(parser: Parser<T>): Parser<Array<T>> => flow(
+  parser,
+  chain(([a, nextInput]) =>
+    pipe(
+      nextInput,
+      many0(parser),
+      map(([ls, inp]): ParserResult<T[]> => [[a, ...ls], inp]),
+    )
+  ),
+  orElse(([_, inp]) => right([[] as T[], inp]))
+)
+
+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]))
+)
+
+export const satify_char = (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 = satify_char(c => /^[0-9]$/g.test(c))
+
+export const integer: Parser<number> = flow(
+  many1(digit),
+  map(([ds, input]) => [parseInt(ds.join(''), 10), input])
+)
+
+export const or = <T>(parsers: Parser<T>[]): Parser<T> => {
+  const ppp = ([p, ...ps]: Parser<T>[]) => flow(
+    p,
+    orElse(([_, inp]) => or(ps)(inp))
+  )
+
+  return parsers.length > 0 ? ppp(parsers) : (inp: string) => left(['unable to match', inp])
+}
+
+export const space = satify_char(c => c === ' ')
+export const newline = satify_char(c => c === '\n')
+export const tab = satify_char(c => c === '\t')
+
+export const whitespace = or([space, newline, tab])
+
-- 
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