Upload rough draft of map patch functionality with test

Right now I'm concerned that the way this generates the code is inefficient, in particular this line:

`in ok @@ (access_path, key', value', loc)`

Since the comments [on my code for the set patch](https://gitlab.com/ligolang/ligo/merge_requests/127)
warned that repeated generation of the access path is a bad idea(?). In any case this does work, so
it's something I can improve on.

src/passes/2-simplify/pascaligo.ml

@@ -119,7 +119,7 @@ module Errors = struct
     ] in
     error ~data title message
 
-  let unsupported_map_patches patch =
+ (* let unsupported_map_patches patch =
     let title () = "map patches" in
     let message () =
       Format.asprintf "map patches (a.k.a. functional updates) are \
@@ -128,7 +128,7 @@ module Errors = struct
       ("patch_loc",
        fun () -> Format.asprintf "%a" Location.pp_lift @@ patch.Region.region)
     ] in
-    error ~data title message
+    error ~data title message *)
 
   let unsupported_set_patches patch =
     let title () = "set patches" in
@@ -817,8 +817,32 @@ and simpl_single_instruction : Raw.single_instr -> (_ -> expression result) resu
       in
       return_statement @@ expr
     )
-  | MapPatch patch ->
-      fail @@ unsupported_map_patches patch
+  | MapPatch patch -> (
+      let (map_p, loc) = r_split patch in
+      let (name, access_path) = simpl_path map_p.path in
+      let%bind inj = bind_list 
+          @@ List.map (fun (x:Raw.binding Region.reg) -> 
+            let (x , loc) = r_split x in
+            let (key, value) = x.source, x.image in
+            let%bind key' = simpl_expression key in
+            let%bind value' = simpl_expression value
+            in ok @@ (access_path, key', value', loc) 
+          )
+        @@ pseq_to_list map_p.map_inj.value.elements in
+      let%bind expr = 
+        let aux = fun (access, key, value, loc) ->
+          let map = e_variable name in 
+          e_assign ~loc name access (e_map_add key value map) in
+        let assigns = List.map aux inj in
+        match assigns with
+        | [] -> ok @@ e_skip ~loc ()
+        | hd :: tl -> (
+            let aux acc cur = e_sequence acc cur in
+            ok @@ List.fold_left aux hd tl
+          )
+      in 
+      return_statement @@ expr
+    )
   | SetPatch patch ->
       fail @@ unsupported_set_patches patch
   | MapRemove r -> (

src/test/contracts/map.ligo

@@ -25,6 +25,10 @@ function rm (var m : foobar) : foobar is block {
   remove 42 from map m
 } with m
 
+function patch_ (var m: foobar) : foobar is block {
+  patch m with map [0 -> 5; 1 -> 6; 2 -> 7]
+} with m
+
 function size_ (const m : foobar) : nat is
   block {skip} with (size(m))
 

src/test/contracts/map.mligo

@@ -11,6 +11,9 @@ let set_ (n : int) (m : foobar) : foobar =
 
 let rm (m : foobar) : foobar = Map.remove 42 m
 
+(* Dummy test so that we can add the same test for PascaLIGO *)
+let patch_ (m : foobar) : foobar = Map.literal [ (0, 5) ; (1, 6) ; (2, 7) ]
+
 let size_ (m : foobar) : nat = Map.size m
 
 let gf (m : foobar) : int = Map.find 23 m

src/test/integration_tests.ml

@@ -411,6 +411,11 @@ let map_ type_f path : unit result =
     let expected = ez [23, 23] in
     expect_eq program "rm" input expected
   in
+  let%bind () =
+    let input = ez [(0,0) ; (1,1) ; (2,2)] in
+    let expected = ez [(0, 5) ; (1, 6) ; (2, 7)] in
+    expect_eq program "patch_" input expected
+  in
   let%bind () =
     let make_input = fun n -> ez List.(map (fun x -> (x, x)) @@ range n) in
     let make_expected = e_nat in