From 016821207f1f2294dd09935a4c1d14d78ff3aed1 Mon Sep 17 00:00:00 2001
From: Akshay Nair <phenax5@gmail.com>
Date: Thu, 13 Jan 2022 21:20:23 +0530
Subject: refactor(parser): reimplements alt parser

---
 src/parser/utils.ts | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

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

diff --git a/src/parser/utils.ts b/src/parser/utils.ts
index 908405e..cee1de7 100644
--- a/src/parser/utils.ts
+++ b/src/parser/utils.ts
@@ -1,4 +1,4 @@
-import { constant, flow, pipe } from 'fp-ts/function'
+import { flow, pipe } from 'fp-ts/function'
 import {
   Either,
   left,
@@ -9,9 +9,10 @@ import {
   fold,
   orElseW,
 } from 'fp-ts/Either'
-import { none, some, Option } from 'fp-ts/Option'
+import { none, some, Option, getOrElse } from 'fp-ts/Option'
 import { fst, mapFst, mapSnd, snd } from 'fp-ts/Tuple'
 import { eq } from '../utils'
+import { prepend } from 'fp-ts/lib/Array'
 
 export type char = string
 
@@ -25,11 +26,19 @@ export const constP =
   (inp: string) =>
     right([v, inp])
 
+export const sepBy1 = <T>(sep: Parser<any>, parser: Parser<T>): Parser<T[]> =>
+  flow(
+    parser,
+    chain(([val, nextInput]) =>
+      pipe(nextInput, many0(prefixed(sep, parser)), map(mapFst(prepend(val)))),
+    ),
+  )
+
 export const many0 = <T>(parser: Parser<T>): Parser<Array<T>> =>
   flow(
     parser,
     chain(([a, nextInput]) =>
-      pipe(nextInput, many0(parser), map(mapFst(ls => [a, ...ls]))),
+      pipe(nextInput, many0(parser), map(mapFst(prepend(a)))),
     ),
     orElse(
       flow(
@@ -134,7 +143,7 @@ export const andThen =
 
 export const optional = <T>(p: Parser<T>): Parser<Option<T>> =>
   flow(
-    p,
+    recoverInput(p),
     fold(
       flow(
         mapFst(_ => none),
-- 
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