closes #166 by adding a drop parameter to string split functions

src/core/CCString.cppo.ml

@@ -309,6 +309,14 @@ let replace ?(which=`All) ~sub ~by s =
       Buffer.contents b
 
 module Split = struct
+  type drop_if_empty = {
+    first: bool;
+    last: bool;
+  }
+
+  let no_drop = {first=false; last=false}
+  let default_drop = no_drop
+
   type split_state =
     | SplitStop
     | SplitAt of int (* previous *)
@@ -316,6 +324,7 @@ module Split = struct
   let rec _split ~by s state = match state with
     | SplitStop -> None
     | SplitAt prev -> _split_search ~by s prev
+
   and _split_search ~by s prev =
     let j = Find.find ~pattern:by s ~start:prev in
     if j < 0
@@ -324,54 +333,64 @@ module Split = struct
 
   let _tuple3 x y z = x,y,z
 
-  let _mkgen ~by s k =
+  let _mkgen ~drop ~by s k =
     let state = ref (SplitAt 0) in
     let by = Find.compile by in
-    fun () ->
+    let rec next() =
       match _split ~by s !state with
         | None -> None
+        | Some (state', 0, 0) when drop.first -> state := state'; next()
+        | Some (_, i, 0) when drop.last && i = length s -> None
         | Some (state', i, len) ->
           state := state';
           Some (k s i len)
+    in
+    next
 
-  let gen ~by s = _mkgen ~by s _tuple3
+  let gen ?(drop=default_drop) ~by s = _mkgen ~drop ~by s _tuple3
 
-  let gen_cpy ~by s = _mkgen ~by s String.sub
+  let gen_cpy ?(drop=default_drop) ~by s = _mkgen ~drop ~by s String.sub
 
-  let _mklist ~by s k =
+  let _mklist ~drop ~by s k =
     let by = Find.compile by in
     let rec build acc state = match _split ~by s state with
       | None -> List.rev acc
+      | Some (state',0,0) when drop.first -> build acc state'
+      | Some (_, i, 0) when drop.last && i=length s -> List.rev acc
       | Some (state', i, len) ->
         build (k s i len ::acc) state'
     in
     build [] (SplitAt 0)
 
-  let list_ ~by s = _mklist ~by s _tuple3
+  let list_ ?(drop=default_drop) ~by s = _mklist ~drop ~by s _tuple3
 
-  let list_cpy ~by s = _mklist ~by s String.sub
+  let list_cpy ?(drop=default_drop) ~by s = _mklist ~drop ~by s String.sub
 
-  let _mkklist ~by s k =
+  let _mkklist ~drop ~by s k =
     let by = Find.compile by in
     let rec make state () = match _split ~by s state with
       | None -> `Nil
+      | Some (state', 0, 0) when drop.first -> make state' ()
+      | Some (_, i, 0) when drop.last && i=length s -> `Nil
       | Some (state', i, len) ->
         `Cons (k s i len , make state')
     in make (SplitAt 0)
 
-  let klist ~by s = _mkklist ~by s _tuple3
+  let klist ?(drop=default_drop) ~by s = _mkklist ~drop ~by s _tuple3
 
-  let klist_cpy ~by s = _mkklist ~by s String.sub
+  let klist_cpy ?(drop=default_drop) ~by s = _mkklist ~drop ~by s String.sub
 
-  let _mkseq ~by s f k =
+  let _mkseq ~drop ~by s f k =
     let by = Find.compile by in
     let rec aux state = match _split ~by s state with
       | None -> ()
+      | Some (state', 0, 0) when drop.first -> aux state'
+      | Some (_, i, 0) when drop.last && i=length s -> ()
       | Some (state', i, len) -> k (f s i len); aux state'
     in aux (SplitAt 0)
 
-  let seq ~by s = _mkseq ~by s _tuple3
+  let seq ?(drop=default_drop) ~by s = _mkseq ~drop ~by s _tuple3
-  let seq_cpy ~by s = _mkseq ~by s String.sub
+  let seq_cpy ?(drop=default_drop) ~by s = _mkseq ~drop ~by s String.sub
 
   let left_exn ~by s =
     let i = find ~sub:by s in
@@ -393,9 +412,9 @@ module Split = struct
 end
 
 let split_on_char c s: _ list =
-  Split.list_cpy ~by:(String.make 1 c) s
+  Split.list_cpy ~drop:Split.no_drop ~by:(String.make 1 c) s
 
-let split = Split.list_cpy
+let split ~by s = Split.list_cpy ~by s
 
 let compare_versions a b =
   let of_int s = try Some (int_of_string s) with _ -> None in
@@ -613,23 +632,43 @@ let of_array a =
 let to_array s =
   Array.init (String.length s) (fun i -> s.[i])
 
-let lines_gen s = Split.gen_cpy ~by:"\n" s
+let lines_gen s = Split.gen_cpy ~drop:{Split.first=false; last=true} ~by:"\n" s
 
-let lines s = Split.list_cpy ~by:"\n" s
+let lines s = Split.list_cpy ~drop:{Split.first=false; last=true} ~by:"\n" s
 
-let concat_gen ~sep g =
+let concat_gen_buf ~sep g : Buffer.t =
   let b = Buffer.create 256 in
   let rec aux ~first () = match g () with
-    | None -> Buffer.contents b
+    | None -> b
     | Some s ->
       if not first then Buffer.add_string b sep;
       Buffer.add_string b s;
       aux ~first:false ()
   in aux ~first:true ()
 
-let unlines l = String.concat "\n" l
+let concat_gen ~sep g =
+  let buf = concat_gen_buf ~sep g in
+  Buffer.contents buf
 
-let unlines_gen g = concat_gen ~sep:"\n" g
+let unlines l =
+  let len = List.fold_left (fun n s -> n + 1 + String.length s) 0 l in
+  let buf = Bytes.create len in
+  let rec aux_blit i l = match l with
+    | [] ->
+      assert (i=len);
+      Bytes.to_string buf
+    | s :: tail ->
+      let len_s = String.length s in
+      Bytes.blit_string s 0 buf i len_s;
+      Bytes.set buf (i+len_s) '\n';
+      aux_blit (i+len_s+1) tail
+  in
+  aux_blit 0 l
+
+let unlines_gen g =
+  let buf = concat_gen_buf ~sep:"\n" g in
+  Buffer.add_char buf '\n';
+  Buffer.contents buf
 
 let set s i c =
   if i<0 || i>= String.length s then invalid_arg "CCString.set";

src/core/CCString.mli

@@ -281,6 +281,14 @@ val lines_gen : string -> string gen
 (** [lines_gen s] returns a generator of the lines of [s] (splits along '\n')
     @since 0.10 *)
 
+(*$= & ~printer:Q.Print.(list @@ Printf.sprintf "%S")
+  ["ab"; "c"] (lines "ab\nc")
+  ["ab"; "c"] (lines "ab\nc\n")
+  [] (lines "")
+  [""] (lines "\n")
+  [""; "a"] (lines "\na")
+*)
+
 val concat_gen : sep:string -> string gen -> string
 (** [concat_gen ~sep g] concatenates all strings of [g], separated with [sep].
     @since 0.10 *)
@@ -293,9 +301,20 @@ val unlines_gen : string gen -> string
 (** [unlines_gen g] concatenates all strings of [g], separated with '\n'
     @since 0.10 *)
 
+(*$= & ~printer:CCFun.id
+  "" (unlines [])
+  "ab\nc\n" (unlines ["ab"; "c"])
+*)
+
 (*$Q
-  Q.printable_string (fun s -> unlines (lines s) = s)
+  Q.printable_string (fun s -> trim (unlines (lines s)) = trim s)
-  Q.printable_string (fun s -> unlines_gen (lines_gen s) = s)
+  Q.printable_string (fun s -> trim (unlines_gen (lines_gen s)) = trim s)
+*)
+
+(*$Q
+  Q.(list string) (fun l -> \
+    let l = unlines l |> lines in \
+    l = (unlines l |> lines))
 *)
 
 val set : string -> int -> char -> string
@@ -477,7 +496,26 @@ end
 (** {2 Splitting} *)
 
 module Split : sig
-  val list_ : by:string -> string -> (string*int*int) list
+  (** Specification of what to do with empty blocks, as in [split ~by:"-" "-a-b-"].
+
+      - [{first=false; last=false}] will return [""; "a"; "b"; ""]
+      - [{first=true; last=false}] will return ["a"; "b" ""]
+      - [{first=false; last=true}] will return [""; "a"; "b"]
+      - [{first=true; last=true}] will return ["a"; "b"]
+
+      The default value of all remaining functions is [Drop_none].
+      @since NEXT_RELEASE
+  *)
+  type drop_if_empty = {
+    first: bool;
+    last: bool;
+  }
+
+  val no_drop : drop_if_empty
+  (** Do not drop any group, even empty and on borders
+      @since NEXT_RELEASE *)
+
+  val list_ : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) list
   (** Eplit the given string along the given separator [by]. Should only
       be used with very small separators, otherwise
       use {!Containers_string.KMP}.
@@ -486,18 +524,18 @@ module Split : sig
       a string from the slice.
       @raise Failure if [by = ""] *)
 
-  val gen : by:string -> string -> (string*int*int) gen
+  val gen : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) gen
 
-  val seq : by:string -> string -> (string*int*int) sequence
+  val seq : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) sequence
 
-  val klist : by:string -> string -> (string*int*int) klist
+  val klist : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) klist
 
   (** {6 Copying functions}
 
       Those split functions actually copy the substrings, which can be
       more convenient but less efficient in general *)
 
-  val list_cpy : by:string -> string -> string list
+  val list_cpy : ?drop:drop_if_empty -> by:string -> string -> string list
 
   (*$T
     Split.list_cpy ~by:"," "aa,bb,cc" = ["aa"; "bb"; "cc"]
@@ -505,11 +543,11 @@ module Split : sig
     Split.list_cpy ~by:" " "hello  world aie" = ["hello"; ""; "world"; "aie"]
   *)
 
-  val gen_cpy : by:string -> string -> string gen
+  val gen_cpy : ?drop:drop_if_empty -> by:string -> string -> string gen
 
-  val seq_cpy : by:string -> string -> string sequence
+  val seq_cpy : ?drop:drop_if_empty -> by:string -> string -> string sequence
 
-  val klist_cpy : by:string -> string -> string klist
+  val klist_cpy : ?drop:drop_if_empty -> by:string -> string -> string klist
 
   val left : by:string -> string -> (string * string) option
   (** Split on the first occurrence of [by] from the leftmost part of