compiler: forbit let rec bindings within function body

Close #13

Author: leostera

src/compiler/ocaml_to_erlang/error.ml

@@ -11,6 +11,15 @@ let ppf = Format.err_formatter
 let file_a_bug =
   {| If you think this is a bug, please file an issue here: https://github.com/AbstractMachinesLab/caramel/issues/new |}
 
+let unsupported_let_rec_inside_of_function_body () =
+  Format.fprintf ppf
+    {|We have found a let rec binding within a function.
+
+This is currently not supported.
+\n
+|};
+  exit 1
+
 let unsupported_let_shadowing name =
   Format.fprintf ppf
     {|We have found that the variable name %s is being shadowed.

src/compiler/ocaml_to_erlang/fun.ml

@@ -327,7 +327,9 @@ and mk_expression exp ~var_names ~modules ~functions ~module_name =
       in
       let branches = if_true :: if_false in
       Erlang.Ast.Expr_case (expr, branches)
-  | Texp_let (_, vbs, expr) ->
+  | Texp_let (Recursive, _, _) ->
+      Error.unsupported_let_rec_inside_of_function_body ()
+  | Texp_let (Nonrecursive, vbs, expr) ->
       (* NOTE: consider flattening let-ins ?
          let rec flatten e acc =
            match e with

tests/compiler/expressions.t/let_bindings.ml

@@ -26,28 +26,3 @@ let let_nested f g h =
   in
   f a
 
-(* FIXME: Erlang does not support let rec bindings, and we're forced to use a
-   combinator instead.
-
-   Right now it believes that the name is supposed to be a module level
-   function, which compiles fine but crashes at runtime.
-
-   So this:
-    let rec f x = f (x + 1) in
-    f 0
-
-   could look like:
-
-     let_rec() ->
-       RecF = fun(G) -> fun (X) -> (G(G))(X+1) end end,
-       F = RecF(RecF),
-       F(0).
-
-   alternatively we coudl wrap this in a support library too
-
-     F = caramel:letrec1(fun (F, X) -> F(X + 1) end)
-
- *)
-let let_rec () =
-  let rec f x = f (x + 1) in
-  f 0

tests/compiler/expressions.t/let_rec.ml

@@ -0,0 +1,25 @@
+(* FIXME: Erlang does not support let rec bindings, and we're forced to use a
+   combinator instead.
+
+   Right now it believes that the name is supposed to be a module level
+   function, which compiles fine but crashes at runtime.
+
+   So this:
+    let rec f x = f (x + 1) in
+    f 0
+
+   could look like:
+
+     let_rec() ->
+       RecF = fun(G) -> fun (X) -> (G(G))(X+1) end end,
+       F = RecF(RecF),
+       F(0).
+
+   alternatively we coudl wrap this in a support library too
+
+     F = caramel:letrec1(fun (F, X) -> F(X + 1) end)
+
+ *)
+let let_rec () =
+  let rec f x = f (x + 1) in
+  f 0

tests/compiler/expressions.t/run.t

@@ -3,6 +3,7 @@
   binding_on_match.ml
   funref.ml
   let_bindings.ml
+  let_rec.ml
   let_shadowing.ml
   list.ml
   literals.ml
@@ -175,7 +176,6 @@
   -export([let_many/0]).
   -export([let_nested/3]).
   -export([let_one/0]).
-  -export([let_rec/0]).
 
   -spec let_one() -> integer().
   let_one() ->
@@ -210,13 +210,6 @@
   end(),
     F(A).
 
-  -spec let_rec() -> any().
-  let_rec() ->
-    F = fun
-    (X) -> f(erlang:'+'(X, 1))
-  end,
-    F(0).
-  
 
   $ caramelc compile list.ml
   File "list.ml", line 7, characters 9-21:
@@ -568,6 +561,7 @@
   $ cat let_shadowing.erl
   cat: let_shadowing.erl: No such file or directory
   [1]
+
   $ caramelc compile names_primes.ml
   Compiling names_primes.erl	OK
   $ cat names_primes.erl
@@ -584,3 +578,12 @@
     X_prime_prime.
 
 
+  $ caramelc compile let_rec.ml
+  We have found a let rec binding within a function.
+  
+  This is currently not supported.
+  \n
+  [1]
+  $ cat let_rec.erl
+  cat: let_rec.erl: No such file or directory
+  [1]