'scanner::readDecimal' succeeds with '0: Int' on empty/malformed input

[jiribenes]

Playground link

import scanner

def lex() = 
  returning::scanner[Char, Int] { 
    readDecimal()
  }

def main() = {
  feed("") {
    println(lex()) // 0
  }
  feed("\n") {
    println(lex()) // 0
  }
  feed("hello") {
    println(lex()) // 0
  }
}

I don't like this behaviour because it silences errors. :(

[jiribenes]

Perhaps already some here instead of many might help:

effekt/libraries/common/scanner.effekt

Lines 91 to 98 in 6288d70

	/// Read a positive decimal number.
	def readDecimal(): Int / Scan[Char] = {
	var result = 0
	for[Int] { many { readDigit() } } { digit =>
	result = result * 10 + digit
	}
	result
	}