add Stdlib.{concat,chop-prefix,chop-suffix}

lib-satysfi/packages/stdlib/stdlib.0.0.1/src/stdlib.satyh

@@ -70,6 +70,9 @@ module Stdlib :> sig
     val persistent ~split-into-grapheme-clusters : string -> list string
     val persistent ~empty : string
     val persistent ~split-into-lines : string -> list (int * string)
+    val persistent ~concat : string -> list string -> string
+    val persistent ~chop-prefix : string -> string -> option string
+    val persistent ~chop-suffix : string -> string -> option string
   end
   module Ordering : sig
     type t = ordering

lib-satysfi/packages/stdlib/stdlib.0.0.1/src/string.satyg

@@ -19,6 +19,9 @@ module String :> sig
   val persistent ~split-into-grapheme-clusters : string -> list string
   val persistent ~empty : string
   val persistent ~split-into-lines : string -> list (int * string)
+  val persistent ~concat : string -> list string -> string
+  val persistent ~chop-prefix : string -> string -> option string
+  val persistent ~chop-suffix : string -> string -> option string
 end = struct
 
   type t = string
@@ -55,4 +58,33 @@ end = struct
 
   val persistent ~split-into-lines = split-into-lines %PRIMITIVE
 
+  val persistent ~concat sep elems =
+    elems |> List.fold-adjacent (fun s elem _ next-opt ->
+      match next-opt with
+      | None    -> s ^ elem
+      | Some(_) -> s ^ elem ^ sep
+      end
+    ) ` `
+
+  val persistent ~rec chop-aux chars-prefix chars-target =
+    match (chars-prefix, chars-target) with
+    | ([], _) ->
+        Some(chars-target)
+    | (prefix-head :: prefix-tail, target-head :: target-tail) ->
+        if prefix-head == target-head then
+          chop-aux prefix-tail target-tail
+        else
+          None
+    | (_, []) ->
+        None
+    end
+
+  val persistent ~chop-prefix prefix target =
+    Option.map from-scalar-values (chop-aux (to-scalar-values prefix) (to-scalar-values target))
+
+  val persistent ~chop-suffix suffix target =
+    let decompose s = List.reverse (to-scalar-values s) in
+    let compose chars = from-scalar-values (List.reverse chars) in
+    Option.map compose (chop-aux (decompose suffix) (decompose target))
+
 end