1 files changed, 94 insertions, 0 deletions
diff --git a/src/parser.ts b/src/parser.ts
new file mode 100644
index 0000000..076e0c5
--- /dev/null
+++ b/src/parser.ts
@@ -0,0 +1,94 @@
+import { flow, pipe } from 'fp-ts/function'
+import { Either, left, right, map, chain, orElse } from 'fp-ts/Either'
+
+export type char = string
+
+export type ParserResult<T> = [T, string]
+export type ParserError = [string, string]
+export type Parser<T> = (input: string) => Either<ParserError, 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(([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 prefixed = <T>(a: Parser<any>, b: Parser<T>): Parser<T> => flow(
+  a,
+  chain(([_, inp]) => b(inp))
+)
+
+export const suffixed = <T>(a: Parser<T>, b: Parser<any>): Parser<T> => flow(
+  a,
+  chain(([out, inp]) => pipe(inp,
+    b,
+    chain(([_, inp2]) => right([out, inp2]))
+  ))
+)
+
+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(([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 matchChar = (ch: char): Parser<char> => satifyChar(c => c === 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> =>
+  s === '' ? constP('') : flow(
+    matchChar(s.charAt(0)),
+    chain(([c, inp]) => pipe(
+      inp,
+      matchString(s.slice(1)),
+      map(([s, inp]) => [c + s, inp]),
+    ))
+  )
+
+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(([v, inp]) => [f(v), inp])
+)
+