Merge pull request #177 from LPCIC/replace-clause

New attribute :replace

Author: gares

CHANGES.md

@@ -1,3 +1,8 @@
+# UNRELEASED
+
+- Elpi:
+  - New attribute `:replace` which replaces a named clause by an unnamed one
+
 # v1.16.9 (March 2023)
 
 Requires Menhir 20211230 and OCaml 4.08 or above.

ELPI.md

@@ -241,7 +241,25 @@ such clause using the `:before` attribute.
 fatal-error Msg :- !, M is "elpi: " ^ Msg, coq-err M.
 ```
 
-The `:after` attribute is also available.
+The `:after` and `:replace` attributes is also available.
+
+The `:replace` attribute cannot be given to a named clause. This is to avoid
+the following ambiguity:
+
+```prolog
+:name "replace-me"
+p 1.
+
+% from one accumulated file
+:replace "replace-me" :name "replace-me"
+p 2.
+
+% from another accumulated file
+:replace "replace-me" :name "replace-me"
+p 3.
+```
+Here the order in which replacement is performed would matter.
+
 
 ## Conditional compilation
 

src/compiler.ml

@@ -559,6 +559,8 @@ end = struct (* {{{ *)
       error ~loc ("duplicate attribute " ^ s) in
     let illegal_err a =
       error ~loc ("illegal attribute " ^ show_raw_attribute a) in
+    let illegal_replace s =
+      error ~loc ("replacing clause for "^ s ^" cannot have a name attribute") in
     let rec aux r = function
       | [] -> r
       | Name s :: rest ->
@@ -570,13 +572,21 @@ end = struct (* {{{ *)
       | Before s :: rest ->
          if r.insertion <> None then duplicate_err "insertion";
          aux { r with insertion = Some (Before s) } rest
+      | Replace s :: rest ->
+          if r.insertion <> None then duplicate_err "insertion";
+          aux { r with insertion = Some (Replace s) } rest
       | If s :: rest ->
          if r.ifexpr <> None then duplicate_err "if";
          aux { r with ifexpr = Some s } rest
       | (External | Index _) as a :: _-> illegal_err a
     in
-    { c with Clause.attributes =
-        aux { insertion = None; id = None; ifexpr = None } attributes }
+    let attributes = aux { insertion = None; id = None; ifexpr = None } attributes in
+    begin
+      match attributes.insertion, attributes.id with
+      | Some (Replace x), Some _ -> illegal_replace x
+      | _ -> ()
+    end;
+    { c with Clause.attributes }
 
   let structure_chr_attributes ({ Chr.attributes; loc } as c) =
     let duplicate_err s =
@@ -590,7 +600,7 @@ end = struct (* {{{ *)
       | If s :: rest ->
          if r.cifexpr <> None then duplicate_err "if";
          aux { r with cifexpr = Some s } rest
-      | (Before _ | After _ | External | Index _) as a :: _ -> illegal_err a 
+      | (Before _ | After _ | Replace _ | External | Index _) as a :: _ -> illegal_err a 
     in
     let cid = Loc.show loc in 
     { c with Chr.attributes = aux { cid; cifexpr = None } attributes }
@@ -614,7 +624,7 @@ end = struct (* {{{ *)
            | Some (Structured.Index _) -> duplicate_err "index"
            | Some _ -> error ~loc "external predicates cannot be indexed"
          end
-      | (Before _ | After _ | Name _ | If _) as a :: _ -> illegal_err a 
+      | (Before _ | After _ | Replace _ | Name _ | If _) as a :: _ -> illegal_err a 
     in
     let attributes = aux None attributes in
     let attributes =
@@ -1910,8 +1920,12 @@ end = struct (* {{{ *)
       match l, loc_name with
       | [],_ -> error ~loc:c.Ast.Clause.loc ("unable to graft this clause: no clause named " ^
              match loc_name with
+             | Ast.Structured.Replace x -> x
              | Ast.Structured.After x -> x
              | Ast.Structured.Before x -> x)
+      | { Ast.Clause.attributes = { Assembled.id = Some n }} :: xs,
+        Ast.Structured.Replace name when n = name ->
+           c :: xs
       | { Ast.Clause.attributes = { Assembled.id = Some n }} as x :: xs,
         Ast.Structured.After name when n = name ->
            c :: x :: xs

src/parser/ast.ml

@@ -133,6 +133,7 @@ type raw_attribute =
   | Name of string
   | After of string
   | Before of string
+  | Replace of string
   | External
   | Index of int list
 [@@deriving show]
@@ -299,7 +300,7 @@ and attribute = {
   id : string option;
   ifexpr : string option;
 }
-and insertion = Before of string | After of string
+and insertion = Before of string | After of string | Replace of string
 and cattribute = {
   cid : string;
   cifexpr : string option

src/parser/ast.mli

@@ -70,6 +70,7 @@ type raw_attribute =
   | Name of string
   | After of string
   | Before of string
+  | Replace of string
   | External
   | Index of int list
 [@@ deriving show]
@@ -205,7 +206,7 @@ and attribute = {
   id : string option;
   ifexpr : string option;
 }
-and insertion = Before of string | After of string
+and insertion = Before of string | After of string | Replace of string
 and cattribute = {
   cid : string;
   cifexpr : string option

src/parser/grammar.mly

@@ -294,6 +294,7 @@ attribute:
 | NAME; s = STRING  { Name s }
 | AFTER; s = STRING { After s }
 | BEFORE; s = STRING { Before s }
+| REPLACE; s = STRING { Replace s }
 | EXTERNAL { External }
 | INDEX; LPAREN; l = nonempty_list(indexing) ; RPAREN { Index l }
 
@@ -393,6 +394,7 @@ constant:
 | NAME { Func.from_string "name" }
 | BEFORE { Func.from_string "before" }
 | AFTER { Func.from_string "after" }
+| REPLACE { Func.from_string "replace" }
 | INDEX { Func.from_string "index" }
 | c = IO { Func.from_string @@ String.make 1 c }
 | CUT { Func.cutf }

src/parser/lexer.mll.in

@@ -164,6 +164,7 @@ and token = parse
 | "sigma" { SIGMA }
 | "after" { AFTER }
 | "before" { BEFORE }
+| "replace" { REPLACE }
 | "name" { NAME }
 | "if" { IF }
 | "index" { INDEX }

src/parser/test_lexer.ml

@@ -14,6 +14,7 @@ type t = Tokens.token =
   | SHORTEN
   | RULE
   | RPAREN
+  | REPLACE
   | RCURLY
   | RBRACKET
   | QUOTED of ( string )

src/parser/tokens.mly

@@ -57,6 +57,7 @@
 %token IF
 %token BEFORE
 %token AFTER
+%token REPLACE
 %token NAME 
 %token INDEX 
 %token CONS

tests/sources/graft_replace_err.elpi

@@ -0,0 +1,9 @@
+pred p o:int.
+:name "replace_me"
+p 1.
+
+:name "foo"
+:replace "replace_me"
+p 2.
+
+main :- fail.