From b3fc08cae05f997e71d846109d400e630b8a4c35 Mon Sep 17 00:00:00 2001
From: Akshay Nair <phenax5@gmail.com>
Date: Fri, 7 Jan 2022 17:51:12 +0530
Subject: feat: adds quantifier suffix parsing + recoverInput for combinators

---
 src/index.ts        | 57 ++++++++++++++++++++++++++++++-----------------------
 src/parser.ts       | 44 ++++++++++++++++++++++++++++++++---------
 src/utils.ts        |  5 +++++
 tests/basic.spec.ts | 13 ++++++++++++
 4 files changed, 85 insertions(+), 34 deletions(-)

diff --git a/src/index.ts b/src/index.ts
index 75bc1af..2ea40eb 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,16 +1,14 @@
-import { constant, flow, identity, pipe } from 'fp-ts/function'
+import { constant, pipe } from 'fp-ts/function'
+import { chain, fold, right } from 'fp-ts/lib/Either'
+import { match } from './utils'
 import {
-  andThen,
   delimited,
-  digit,
-  integer,
   many1,
   mapTo,
-  matchChar,
   optional,
   or,
-  pair,
   Parser,
+  ParserResult,
   symbol,
   tuple3,
 } from './parser'
@@ -36,16 +34,13 @@ export const anyBool = mapTo(
 )
 export const truthy = mapTo(symbol('\\T'), constant({ tag: 'Truthy' } as Expr))
 export const falsey = mapTo(symbol('\\F'), constant({ tag: 'Falsey' } as Expr))
-// export const optional = mapTo(symbol('?'), constant({ tag: 'Optional' } as Expr))
-// export const zeroOrMore = mapTo(symbol('*'), constant({ tag: 'ZeroOrMore' } as Expr))
-// export const oneOrMore = mapTo(symbol('+'), constant({ tag: 'OneOrMore' } as Expr))
 
 type Expr =
   | { tag: 'Start' }
   | { tag: 'End' }
-  | { tag: 'Optional' }
-  | { tag: 'OneOrMore' }
-  | { tag: 'ZeroOrMore' }
+  | { tag: 'Optional'; expr: Expr }
+  | { tag: 'OneOrMore'; expr: Expr }
+  | { tag: 'ZeroOrMore'; expr: Expr }
   | { tag: 'NextItem' }
   | { tag: 'AnyItem' }
   | { tag: 'Or' }
@@ -56,13 +51,35 @@ type Expr =
   | { tag: 'Falsey' }
   | { tag: 'Group'; exprs: Expr[] }
 
+export const wrapQuantifiers: (e: ParserResult<Expr>) => ParserResult<Expr> =
+  chain(([expr, input]) =>
+    pipe(
+      input,
+      or([symbol('*'), symbol('+'), symbol('?')]),
+      fold(
+        () => right([expr, input]),
+        ([c, inp]) =>
+          pipe(
+            c,
+            match<Expr, string>({
+              '*': () => ({ tag: 'ZeroOrMore', expr }),
+              '+': () => ({ tag: 'OneOrMore', expr }),
+              '?': () => ({ tag: 'Optional', expr }),
+              _: () => expr,
+            }),
+            (ex) => right([ex, inp])
+          )
+      )
+    )
+  )
+
 export const expressionP: Parser<Expr> = (input: string) =>
   pipe(
     input,
     or([
       mapTo(
         delimited(symbol('('), many1(expressionP), symbol(')')),
-        (exprs) => ({ tag: 'Group', exprs })
+        (exprs) => ({ tag: 'Group', exprs } as Expr)
       ),
       nextItem,
       anyItem,
@@ -71,27 +88,17 @@ export const expressionP: Parser<Expr> = (input: string) =>
       anyBool,
       truthy,
       falsey,
-    ])
+    ]),
+    wrapQuantifiers
   )
 
 export const parser = tuple3(optional(start), many1(expressionP), optional(end))
 
 /*
 
-^ $ => start and end of list
-? => optional
-. => any item
-* => 0 or more instances
-+ => 1 or more instances
 {3,6} => 3 to 6 instances
-\s => string
-\n => number
-\b => boolean
-\T => truthy
-\F => falsey
 (> 5) => number greater than
 (< 5) => number less than
-, => followed by
 [name x] => apply x on property `name`
 | => or
 /x/ => match regular expression (string values in list)
diff --git a/src/parser.ts b/src/parser.ts
index baa3e76..a7d6528 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -1,14 +1,24 @@
-import { flow, pipe } from 'fp-ts/function'
-import { Either, left, right, map, chain, orElse, fold } from 'fp-ts/Either'
+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, snd } from 'fp-ts/Tuple'
+import { mapFst, mapSnd, snd } from 'fp-ts/Tuple'
 import { eq } from './utils'
 
 export type char = string
 
-export type ParserResult<T> = [T, string]
+export type ParserState<T> = [T, string]
 export type ParserError = [string, string]
-export type Parser<T> = (input: string) => Either<ParserError, ParserResult<T>>
+export type ParserResult<T> = Either<ParserError, ParserState<T>>
+export type Parser<T> = (input: string) => ParserResult<T>
 
 export const constP =
   <T>(v: T): Parser<T> =>
@@ -39,13 +49,29 @@ export const many1 = <T>(parser: Parser<T>): Parser<Array<T>> =>
     )
   )
 
+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> =>
-  flow(a, chain(flow(snd, b)))
+  recoverInput(flow(a, chain(flow(snd, b))))
 
 export const suffixed = <T>(a: Parser<T>, b: Parser<any>): Parser<T> =>
-  flow(
-    a,
-    chain(([out, inp]) => pipe(inp, b, map(mapFst((_) => out))))
+  recoverInput(
+    flow(
+      a,
+      chain(([out, inp]) => pipe(inp, b, map(mapFst((_) => out))))
+    )
   )
 
 export const delimited = <T>(
diff --git a/src/utils.ts b/src/utils.ts
index e7392bf..9c4c97b 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -2,3 +2,8 @@ export const eq =
   <T>(a: T) =>
   (b: T): boolean =>
     a === b
+
+export const match =
+  <R, K extends string>(pattern: { [key in K | '_']: () => R }) =>
+  (k: K): R =>
+    (pattern[k] || pattern._)()
diff --git a/tests/basic.spec.ts b/tests/basic.spec.ts
index b0a4d50..4e0a938 100644
--- a/tests/basic.spec.ts
+++ b/tests/basic.spec.ts
@@ -45,5 +45,18 @@ describe('Foobar', () => {
       ],
       ''
     ]))
+
+    expect(parser(/^ \s* \T? \n+ $/.source)).toEqual(right([
+      [
+        some({ tag: 'Start' }),
+        [
+          { tag: 'ZeroOrMore', expr: { tag: 'AnyString' } },
+          { tag: 'Optional', expr: { tag: 'Truthy' } },
+          { tag: 'OneOrMore', expr: { tag: 'AnyNumber' } },
+        ],
+        some({ tag: 'End' }),
+      ],
+      ''
+    ]))
   })
 })
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