feat: adds more parser combinators

3 files changed, 40 insertions, 2 deletions

diff --git a/src/index.ts b/src/index.ts
index d236473..582f9be 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,5 @@
 import { constant, flow, identity, pipe } from 'fp-ts/function'
-import { mapTo, symbol } from './parser'
+import { andThen, delimited, mapTo, optional, pair, symbol } from './parser'
 
 export const start = mapTo(symbol('^'), constant({ tag: 'Start' } as Expr))
 export const end = mapTo(symbol('$'), constant({ tag: 'End' } as Expr))
@@ -27,6 +27,16 @@ type Expr =
   | { tag: 'Truthy' }
   | { tag: 'Falsey' }
 
+export const expressionP = symbol('fuck')
+
+export const parser = pair(
+  pair(
+    optional(start),
+    expressionP,
+  ),
+  optional(end),
+)
+
 /*
 
 ^ $ => start and end of list
diff --git a/src/parser.ts b/src/parser.ts
index f8dcd44..5ccba43 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -1,5 +1,6 @@
 import { flow, pipe } from 'fp-ts/function'
-import { Either, left, right, map, chain, orElse } from 'fp-ts/Either'
+import { Either, left, right, map, chain, orElse, fold } from 'fp-ts/Either'
+import { none, some, Option } from 'fp-ts/lib/Option'
 
 export type char = string
 
@@ -117,3 +118,24 @@ export const mapTo = <I, R>(p: Parser<I>, f: (p: I) => R): Parser<R> =>
     p,
     map(([v, inp]) => [f(v), inp])
   )
+
+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(
+      ([_, inp]) => right([none, inp]),
+      ([v, inp]) => right([some(v), inp])
+    )
+  )
+
+export const pair = <A, B>(a: Parser<A>, b: Parser<B>): Parser<[A, B]> => pipe(
+  a,
+  andThen(ra => mapTo(b, rb => [ra, rb]))
+)
+
diff --git a/tests/basic.spec.ts b/tests/basic.spec.ts
index eeeb121..962f076 100644
--- a/tests/basic.spec.ts
+++ b/tests/basic.spec.ts
@@ -9,7 +9,9 @@ import {
   whitespaces0,
   delimited,
   symbol,
+  optional,
 } from '../src/parser'
+import { parser } from '../src'
 
 describe('Foobar', () => {
   it('should do shit', () => {
@@ -26,4 +28,8 @@ describe('Foobar', () => {
       right([2, '0 '])
     )
   })
+
+  it('should maybeshut', () => {
+    console.log(JSON.stringify(parser('fuck'), null, 2))
+  })
 })