language server over stdio, emacs mode with repl and eglot wiring

2 files changed, 34 insertions, 10 deletions

diff --git a/lib/front.ml b/lib/front.ml
index 7cacc20..b728825 100644
--- a/lib/front.ml
+++ b/lib/front.ml
@@ -1,14 +1,27 @@
-let parse_string source =
+type error = { line : int; column : int; message : string }
+
+let position lexbuf =
+  let p = lexbuf.Lexing.lex_curr_p in
+  (p.Lexing.pos_lnum, p.Lexing.pos_cnum - p.Lexing.pos_bol)
+
+let parse source =
   let lexbuf = Lexing.from_string source in
   match Parser.program Lexer.token lexbuf with
   | statements -> Ok statements
   | exception Lexer.Error message ->
-      let position = lexbuf.Lexing.lex_curr_p in
-      Error
-        (Printf.sprintf "lexical error at line %d: %s"
-           position.Lexing.pos_lnum message)
+      let line, column = position lexbuf in
+      Error { line; column; message }
   | exception Parser.Error ->
-      let position = lexbuf.Lexing.lex_curr_p in
+      let line, column = position lexbuf in
       Error
-        (Printf.sprintf "syntax error at line %d, before %S"
-           position.Lexing.pos_lnum (Lexing.lexeme lexbuf))
+        {
+          line;
+          column;
+          message = Printf.sprintf "syntax error before %S" (Lexing.lexeme lexbuf);
+        }
+
+let parse_string source =
+  match parse source with
+  | Ok statements -> Ok statements
+  | Error { line; message; _ } ->
+      Error (Printf.sprintf "line %d: %s" line message)
diff --git a/lib/front.mli b/lib/front.mli
index 00fa65f..a4e91e6 100644
--- a/lib/front.mli
+++ b/lib/front.mli
@@ -1,7 +1,18 @@
 (** Front door: text to statements.
 
     Wraps the generated lexer and parser so callers see one total
-    function from source text to syntax or a positioned message.
-    The REPL, the file runner, and the tests all enter here. *)
+    function from source text to syntax or a positioned error. The
+    REPL, the file runner, the LSP server, and the tests all enter
+    here. *)
+
+type error = {
+  line : int;  (** 1-based, as editors count *)
+  column : int;  (** 0-based character offset in the line *)
+  message : string;
+}
+
+val parse : string -> (Ast.statement list, error) result
 
 val parse_string : string -> (Ast.statement list, string) result
+(** [parse] with the position folded into the message, for callers
+    that only print. *)