Smalltalk: how to check wether a string contains only numbers?

Question

so basically I have some input possibilities for the user where should only numbers be accepted, otherwise the user will be alerted his input was incorrect.

the input is considered a String when I read it out using a callback. now I want to check whether the string(which SHOULD contain numbers) actually DOES ONLY contain numbers, but I didnt find a solution implemented already. i tried

theString isInteger 

-is never true for the string

theString asNumber 

- ignores letters, but I want to have a clear output wether letters are included in the string or not

theString isNumber

- always false

Answer 1

In Squeak and Pharo, you have the message #isAllDigits that does exactly what you want:

'1233248539487523' isAllDigits "--> true"

Answer 2

You can use a regular expression to check that the string contains only numbers:

theString matchesRegex: '\d+'

or a more complex regular expression to also allow an optional sign and decimal point:

theString matchesRegex: '-?\\d+(\\.\\d+)?'

Answer 3

Unfortunately, I could not locate messages 'isAllDigits' or 'matchesRegex'on Cincom Smalltalk. However, what you could do is extract a word from the string and convert it to a number using asNumber. So, if the returned value is 0(zero) it means that either the number is actually a 0(which could e checked with an additional condition) or string did not contain a digit/number.

Answer 4

This should work with many Smalltalks dialects:

(aString detect: [:c| c isDigit not ]) isNil ifTrue: [ "it's a number" ].