[LIGO-168] Add the while loop to CameLIGO

src/passes/operators/operators.ml

@@ -194,6 +194,10 @@ module Simplify = struct
       ("List.map" , "LIST_MAP") ;
       ("List.fold" , "LIST_FOLD") ;
 
+      ("Loop.fold_while" , "FOLD_WHILE") ;
+      ("continue" , "CONTINUE") ;
+      ("stop" , "STOP") ;
+
       ("Operation.transaction" , "CALL") ;
       ("Operation.get_contract" , "CONTRACT") ;
       ("int" , "INT") ;
@@ -563,6 +567,25 @@ module Typer = struct
     let%bind () = assert_eq_1 ~msg:"res init" res init in
     ok res
 
+  (** FOLD_WHILE is a fold operation that takes an initial value of a certain type
+      and then iterates on it until a condition is reached. The auxillary function
+      that does the fold returns either boolean true or boolean false to indicate
+      whether the fold should continue or not. Necessarily then the initial value
+      must match the input parameter of the auxillary function, and the auxillary
+      should return type (bool * input) *)
+  let fold_while = typer_2 "FOLD_WHILE" @@ fun init body ->
+    let%bind (arg, result) = get_t_function body in
+    let%bind () = assert_eq_1 arg init in
+    let%bind () = assert_eq_1 (t_pair (t_bool ()) init ()) result
+    in ok init
+
+  (* Continue and Stop are just syntactic sugar for building a pair (bool * a') *)
+  let continue = typer_1 "CONTINUE" @@ fun arg ->
+    ok @@ t_pair (t_bool ()) arg ()
+
+  let stop = typer_1 "STOP" @@ fun arg ->
+    ok (t_pair (t_bool ()) arg ())
+
   let not_ = typer_1 "NOT" @@ fun elt ->
     if eq_1 elt (t_bool ())
     then ok @@ t_bool ()
@@ -641,6 +664,9 @@ module Typer = struct
       map_find_opt ;
       map_map ;
       map_fold ;
+      fold_while ;
+      continue ;
+      stop ;
       map_iter ;
       map_get_force ;
       map_get ;
@@ -726,6 +752,13 @@ module Compiler = struct
     ("MAP_FIND_OPT" , simple_binary @@ prim I_GET) ;
     ("MAP_ADD" , simple_ternary @@ seq [dip (i_some) ; prim I_UPDATE]) ;
     ("MAP_UPDATE" , simple_ternary @@ prim I_UPDATE) ;
+    ("FOLD_WHILE" , simple_binary @@ seq [(i_push (prim T_bool) (prim D_True)) ;
+                                          prim ~children:[seq [dip i_dup; i_exec; i_unpair]] I_LOOP ;
+                                          i_swap ; i_drop]) ;
+    ("CONTINUE" , simple_unary @@ seq [(i_push (prim T_bool) (prim D_True)) ;
+                                       i_pair]) ;
+    ("STOP" , simple_unary @@ seq [(i_push (prim T_bool) (prim D_False)) ;
+                                   i_pair]) ;
     ("SIZE" , simple_unary @@ prim I_SIZE) ;
     ("FAILWITH" , simple_unary @@ prim I_FAILWITH) ;
     ("ASSERT_INFERRED" , simple_binary @@ i_if (seq [i_failwith]) (seq [i_drop ; i_push_unit])) ;

src/test/contracts/loop.mligo

@@ -0,0 +1,33 @@
+(* Test loops in CameLIGO *)
+
+let aux_simple (i: int) : bool * int =
+  if i < 100 then continue (i + 1) else stop i
+
+let counter_simple (n: int) : int =
+  Loop.fold_while n aux_simple
+
+type sum_aggregator = {
+  counter : int ;
+  sum : int ;
+}
+
+let counter (n : int) : int =
+  let initial : sum_aggregator = { counter = 0 ; sum = 0 } in
+  let out : sum_aggregator = Loop.fold_while initial (fun (prev: sum_aggregator) ->
+    if prev.counter <= n then
+      continue ({ counter = prev.counter + 1 ; sum = prev.counter + prev.sum })
+    else
+      stop ({ counter = prev.counter ; sum = prev.sum })
+  ) in out.sum
+
+let aux_nest (prev: sum_aggregator) : bool * sum_aggregator =
+  if prev.counter < 100 then
+    continue ({ counter = prev.counter + 1 ;
+                sum = prev.sum + Loop.fold_while prev.counter aux_simple})
+  else
+    stop ({ counter = prev.counter ; sum = prev.sum })
+
+let counter_nest (n: int) : int =
+  let initial : sum_aggregator = { counter = 0 ; sum = 0 } in
+  let out : sum_aggregator = Loop.fold_while initial aux_nest
+  in out.sum

src/test/integration_tests.ml

@@ -805,6 +805,24 @@ let for_fail () : unit result =
   let%bind () = expect_fail program "main" (e_nat 0)
   in ok () *)
 
+let loop_mligo () : unit result =
+  let%bind program = mtype_file "./contracts/loop.mligo" in
+  let%bind () =
+    let input = e_int 0 in
+    let expected = e_int 100 in
+    expect_eq program "counter_simple" input expected
+  in
+  let%bind () =
+    let input = e_int 100 in
+    let expected = e_int 5050 in
+    expect_eq program "counter" input expected
+  in
+  let%bind () =
+    let input = e_int 100 in
+    let expected = e_int 10000 in
+    expect_eq program "counter_nest" input expected
+  in ok ()
+
 let matching () : unit result =
   let%bind program = type_file "./contracts/match.ligo" in
   let%bind () =
@@ -1152,6 +1170,7 @@ let main = test_suite "Integration (End to End)" [
     test "big_map (mligo)" mbig_map ;
     test "list" list ;
     test "loop" loop ;
+    test "loop (mligo)" loop_mligo ;
     test "matching" matching ;
     test "declarations" declarations ;
     test "quote declaration" quote_declaration ;