Add skip statement

ast.ml

@@ -36,6 +36,7 @@ and stmt =
   | Sfor of stmt * expr * stmt * block
   | Sprint of expr
   | Sexit
+  | Sskip
 
 and block =
   | Bstmt of stmt

compiler.ml

@@ -63,7 +63,8 @@ let rec compile_stmt ?(label = "") s env li =
     compile_expr e env 0 li @ labeled_inst ~label:("wcond"^sct) ("BRANCHIFNOT wdone"^sct) @ compile_block b env li @ compile_expr e env 0 li @ ["BRANCH wcond" ^ sct] @ labeled_inst ~label:("wdone"^sct) ""
   | Sfor (s1,e,s2,b) -> compile_stmt s1 env li @ compile_stmt (Swhile (e, Bseq_r (b,s2))) env li
   | Sprint e -> (compile_expr ~label:label e env 0 li) @ ["PRIM print"]
-  | Sexit -> ["STOP"] @ li
+  | Sexit -> labeled_inst ~label:label ("STOP") @ li
+  | Sskip -> labeled_inst ~label:label ("CONST 0") @ li
 
 and compile_block ?(label = "") b env li =
   match b with

lexer.mll

@@ -58,6 +58,7 @@ rule token = parse
   | "print"       { PRINT }
   | "array_size"  { ARRAY_SIZE }
   | "exit"        { EXIT }
+  | "skip"        { SKIP }
   | "(*"          { comment lexbuf }
   | boolean as b  { CST (Cbool (bool_of_string b)) }
   | integer as s  { CST (Cint (int_of_string s)) }

parser.mly

@@ -11,7 +11,7 @@
 
 %token <Ast.constant> CST
 %token LET IN REF BEGIN END IF THEN ELSE WHILE DO DONE FOR AND OR NOT
-%token PRINT ARRAY_SIZE EXIT
+%token PRINT ARRAY_SIZE EXIT SKIP
 %token EOF
 %token COMMA SEMICOLON EXCL LP RP LSQ RSQ LCU RCU
 %token EQUAL REF_EQUAL CMP_EQ CMP_NEQ CMP_LT CMP_LE CMP_GT CMP_GE
@@ -45,6 +45,7 @@ stmt :
      | FOR s1=stmt SEMICOLON e=expr SEMICOLON s2=stmt DO b=block DONE { Ast.Sfor (s1, e, s2, b) }
      | PRINT e=expr { Ast.Sprint e }
      | EXIT { Ast.Sexit }
+     | SKIP { Ast.Sskip }
      ;
 
 block :

tests/t12.txt

@@ -0,0 +1,13 @@
+let i = (ref ()) in
+begin
+  print 42;
+  skip;
+  print 27;
+  for i:=1 ; ((!i)<=10) ; i:=((!i)+1) do
+    if ((!i) < 5) then
+      print (!i)
+    else
+      skip
+  done;
+  print 42
+end