Regular Expressions in Standard ML

(* Standard ML offers support for regular expressions through libraries.
   Here are some examples of common regexp-related tasks in Standard ML. *)

(* We'll use the SML/NJ library for regular expressions *)
structure Regexp = RegExpFn(structure P = AwkSyntax structure E = DfaEngine)

fun main () =
  let
    (* This tests whether a pattern matches a string *)
    val match = Regexp.match (Regexp.fromString "p[a-z]+ch") "peach"
    val _ = print (Bool.toString match ^ "\n")

    (* For other regexp tasks, we'll compile the pattern *)
    val r = Regexp.fromString "p([a-z]+)ch"

    (* Here's a match test like we saw earlier *)
    val _ = print (Bool.toString (Regexp.match r "peach") ^ "\n")

    (* This finds the match for the regexp *)
    val findString = case Regexp.find r (Substring.full "peach punch") of
                         SOME (_, match) => Substring.string match
                       | NONE => ""
    val _ = print (findString ^ "\n")

    (* This returns the start and end indexes for the match *)
    val findStringIndex = case Regexp.find r (Substring.full "peach punch") of
                              SOME (start, match) => 
                                "idx: [" ^ Int.toString start ^ " " ^ 
                                Int.toString (start + Substring.size match) ^ "]"
                            | NONE => "idx: []"
    val _ = print (findStringIndex ^ "\n")

    (* The 'extract' function includes information about both the whole-pattern matches
       and the submatches within those matches *)
    val submatch = case Regexp.extract r (Substring.full "peach punch") of
                       SOME [whole, sub] => "[" ^ whole ^ " " ^ sub ^ "]"
                     | _ => "[]"
    val _ = print (submatch ^ "\n")

    (* Finding all matches for a regexp *)
    fun findAll text =
      let
        fun loop start acc =
          case Regexp.find r (Substring.extract (text, start, NONE)) of
              SOME (pos, match) => 
                loop (start + pos + Substring.size match) 
                     (Substring.string match :: acc)
            | NONE => List.rev acc
      in
        loop 0 []
      end
    
    val allMatches = findAll "peach punch pinch"
    val _ = print (String.concatWith " " allMatches ^ "\n")

    (* Replacing subsets of strings *)
    val replaced = Regexp.substitute r (fn _ => "<fruit>") "a peach"
    val _ = print (replaced ^ "\n")

    (* Transforming matched text with a function *)
    val transformed = Regexp.substitute r (fn s => String.map Char.toUpper s) "a peach"
    val _ = print (transformed ^ "\n")
  in
    ()
  end

val _ = main()

This Standard ML code demonstrates similar functionality to the Go example, using the SML/NJ regular expression library. Here are some key points:

We use the RegExpFn functor to create a Regexp structure with Awk-like syntax and DFA engine.
Pattern matching is done using Regexp.match and Regexp.find functions.
Submatches are extracted using the Regexp.extract function.
To find all matches, we implement a recursive findAll function.
String replacement is done using the Regexp.substitute function.
Standard ML doesn’t have built-in regular expression support, so we rely on the SML/NJ library.
Some operations, like finding string indexes, require manual calculation based on substring positions.
Error handling is mostly done through pattern matching on SOME and NONE values.

Note that the exact output might differ slightly from the Go version due to differences in how Standard ML handles regular expressions and string operations. Also, some advanced features might not be directly available or might require more complex implementations in Standard ML.

Text Templates in Standard ML

Random Numbers in Standard ML

Learn X By Example

Title here

Regular Expressions in Standard ML