Add string functions

[jimscarver]

Introduction/Motivation/Abstract

develops expect standard string functions including converting other types toString()

Motivating Examples

Examples

• S.length is the length of the string in characters;
• S.substring(i) returns the part of the string starting at index i.
• S.substring(i,j) returns the part of the string starting at index i and going up to index j-1. You can write S.slice(i,j) instead.
• S.contains(T) returns true if T is a substring of S;
• S.indexOf(T) returns the index of the first occurrence of the substring T in S (or -1);
• S.indexOf(T, i) returns the index of the first occurrence after index i of the substring T in S (or -1);
• S.toLowerCase and S.toUpperCase return a copy of the string with all characters converted to lower or upper case;
• S.capitalize returns a new string with the first letter only converted to upper case;
• S.reverse returns the string backwards;
• S.isEmpty is the same as S.length == 0;
• S.nonEmpty is the same as S.length != 0;
• S.startsWith(T) returns true if S starts with T;
• S.endsWith(T) returns true if S ends with T;
• S.replace(c1, c2) returns a new string with all characters c1 replaced by c2;
• S.replace(T1, T2) returns a new string with all occurrences of the substring T1 replaced by T2;
• S.trim returns a copy of the string with white space at both ends removed;
• S.format(arguments) returns a string where the percent-placeholders in S have been replaced by the arguments (see example below);
• S.split(T) splits the string into pieces and returns an array with the pieces. T is a regular expression (not explained here). To split around white space, use S.split("s+").

Please check the ones we already have. This is a good first issue for someone.

Comparison Examples

I struggled to concatenate a number and a string ultimately discovering it is impossible in rholag. Nothing should be impossible in rholang.

Counter-Examples

Design

Counter-Examples

Drawbacks

Alternatives

References

[jimscarver]

We also need a simple String.match capability being considered in #14

[dckc]

...
I struggled to concatenate a number and a string ultimately discovering it is impossible in rholag.

Are you quite sure about that, @jimscarver ? String interpolation works when I try it in the rholang playground:

new x in {
  x!("${n}${s}" %% {"n": 123, "s": "abc"})
}

Result

[
  "123abc"
]

[jimscarver]

There are many other string functions that are needed like case conversion, finding a substring, and matching patterns.

Regular expressions prove to be problematical due to recursion see #19 however filename "glob" pattern matching like [Ss]ubstring are not recursive and could be supported easily https://index.scala-lang.org/salva/scala-glob/scala-glob/0.0.3?

We can also support more types for existing functions easily like string.contains(substring). Any type that makes sense in a function should be supported. This could be done even by scala newbees