Scalatin

Simple monadic input scanner library for Scala.

Scalatin is meant to be used in competitive programming i.e. AtCoder.

Example

import StdInScanner._

// input:
// 1
// 2 3
// test

val scanner = for {
  a      <- readInt
  (b, c) <- readIntPair
  s      <- readLine
} yield (a+b+c, s)

val (sum, s) = scanner.run
// sum = 6
// s = "test"

Usage

• In code submission, copy/paste library code block indicated by comment.
• For testing, StdInScannerSyntaxForTesting might be useful. It adds some extension methods to StdInScanner that enable to run scanner on stub input(file or string litral).
  • #runOnFile(filename): run scanner on the specified file.
  • #runOnString(str): run scanner on the supplied string.

List of All Scanners

Pure scanners(read nothing)

• StdinScanner.of[A](a: A): Always emit constant a. Read nothing from input.

StdInScanner.of(1).run
// 1

// input:
// hoge

val sc = for {
  c <- StdInScanner.of(42)
  s <- readLine
} yield (c, s)

val (c, s) = sc.run
// c = 42
// s = "hoge"

• unit: always emit ()(value of type Unit). Read nothing from input.

Read single line, produce single value

• readLine: Read a line as String.

• read{Int/Long/BigInt}: Read a line as Int/Long/BigInt.

// input:
// 1234
// hoge

val sc = for {
  i <- readInt
  s <- readLine
} yield (i, s)

val (i, s) = sc.run
// i = 1234
// s = "hoge"

• readPair[A, B](fa, fb): Read a line as a pair of strings(separated by a whitespace) and convert each element by the supplied functions fa, fb.

• read{String/Int/Long}Pair: Read a line as a pair of String/Int/Long s.

// input:
// hoge true

val (a, b) = readPair(_.toUpperCase, _.toBoolean).run
// a = "HOGE"
// b = true: Boolean

// input:
// 100 200

val (m, n) = readIntPair.run
// m = 100
// n = 200

• readTriple[A, B, C](fa, fb, fc): Read a line as a triple of strings(sep. by a whitespace) and convert each element by supplied functions.

• read{String/Int/Long}Triple: Read a line as a triple of String/Int/Long s.

Read single line, produce list of values

note: Container type of produced values is Vector by default.

• readTokensWithMap[A](f): Read a line as a list of tokens(strings sep. by whitespace) and map over the list by the supplied function.

• readTokens / read{Int/Long/BigInt}Tokens: Read a line as a list of String/Int/Long/BigInt.

// input:
// 1 1 2 3 5 8

val v = readIntTokens.run
// v =  Vector(1, 1, 2, 3, 5, 8)

Read multiple lines, produce list of values

note: Container type of produced values is Vector by default.

• readLinesWithMap[A](n: Int, f): Read n lines as a list of strings and map over the list by the supplied function.

• readLines(n: Int) / read{Ints/Longs/BigInts}(n: Int): Read n lines as a list of String/Int/Long/BigInt s.

// input:
// 3 2
// 123
// 456
// 789
// hoge
// fuga

val sc = for {
  (m, n) <- readIntPair
  a <- readInts(m)
  b <- readLines(n)
} yield (a, b)

val (a, b) = sc.run
// a = Vector(123, 456, 789)
// b = Vector("hoge", "fuga")

• readPairs[A, B](n: Int)(fa, fb): Read n lines as a list of pairs(sep. by whitespace) and convert each element of pairs in the list by the supplied functions.

• readIntPairs(n: Int): Read n lines as a list of Int's pairs.

// input:
// a 1
// b 2
// c 3

val ps = readPairs(3)(_.toUpperCase, _.toInt).run
// ps = Vector(("A", 1), ("B", 2), ("C", 3))

• readTriples[A, B, C](n: Int)(fa, fb, fc) / readIntTriples(n: Int): analogous to readPairs / readIntPairs, produce triples instead of pairs.

Read multiple lines, produce matrix of values

note: Container type of produced values is type Matrix[A] = Vector[Vector[A]] by default.

• readMatrixWithMap[A](nRows: Int, f): Read n lines as matrix(each line corresponds a row, each token corresponds a column of the row), and map over the matrix by the supplied function.

• readMatrix(nRows: Int) / read{Int/Long/BigInt}Matrix(nRows: Int): Read n lines as matrix of String/Int/Long/BigInt s.

// input:
// 3
// 1 2 3
// 4 5 6
// 7 8 9

val sc = for {
  nRows <- readInt
  mat <- readIntMatrix(nRows)
} yield mat

val mat = sc.run
// mat = Vector(
//  Vector(1, 2, 3),
//  Vector(4, 5, 6),
//  Vector(7, 8, 9))

Notice

• If the input can't be parsed as the type specified by the scanner(i.e. Int in readInt/readInts etc.), it just throws exception. Since Scalatin is meant to be used only to read competitive programming's inputs, sophisticated error handling system is not provided.

License

Licensed under Apache License, Version 2.0.