Function Template not working : segfaults

Google Group
1

I have not programmed in ATS for a while , so I was trying to review ATS
and tried to implement Maybe monad from this discussion thread :
https://groups.google.com/forum/#!searchin/ats-lang-users/monad/ats-lang-users/gGOqTJwiegE/K8ieRTSodDEJ

#include “share/atspre_define.hats”
#include “share/atspre_staload.hats”

datatype Maybe (a : t@ype) =
| Nothing (a) of ()
| Just (a) of (a)

datatype Expr =
| Val of Int
| Div of (Expr , Expr)

(* from UPENN haskell example )
( ok = Div (Div (Val 1972) (Val 2)) (Val 23) *)
val ok = Div (Div ( Val (1972) , Val (2) ) , Val (23))

(* val err = Div (Val 2) (Div (Val 1) (Div (Val 2) (Val 3))) *)
val err = Div (Val (2) , Div (Val (1) , Div (Val (2) , Val (3))))

abst@ype M (t@ype) = ptr

extern
fun {a : t@ype}
ret (v : a ) : M(a)

extern
fun{a,b : t@ype}
bind : M(a) -> M(b)

extern
fun{a,b:t@ype}
bind$cont (x : a) : M(b)

assume M (a : t@ype) = Maybe (a)

extern
fun div (m : int , n : int) : Maybe(int)

implement{a}
ret (x) = Just (x)

implement{a,b}
bind (ma) =
case ma of
| Nothing _ => Nothing ()
| Just (x) => bind$cont<a,b> (x)

fun eval (e : Expr) : Maybe(int) =
case e of
| Val n => ret (n)
| Div (e1 , e2) =>
bind<int,int>(eval (e1)) where {
implement bind$cont<int,int> (m) =
bind<int,int>(eval (e2)) where {
implement bind$cont<int,int> (n) = div (m,n) }}

implement
div (m , n) =
if n = 0
then Nothing ()
else ret (m / n)

fun print_maybe (m : Maybe (int)) : void =
case m of
| Nothing _ => println! (“Nothing”)
| Just (x) => println! (x)

implement main0 () = () where {
val res1 = eval (ok)
val res2 = eval (err)
val _ = print_maybe (res1)
val _ = print_maybe (res2)
}

When run this segfaults , and I think it is because it does not see second
implementation of bind$cont and keep calling the first one which leads to
stack overflow .
Does not second implementation override the first one ?

2

By the way, for a better error message in a case like this you may want to try something like https://github.com/NixOS/nix/blob/master/src/libmain/stack.cc#L17-L38 https://github.com/NixOS/nix/blob/master/src/libmain/stack.cc#L17-L38> On Apr 2, 2015, at 7:48 AM, gmhwxi gmh...@gmail.com wrote:

Your assessment of the situation sounds correct to me. However, I don’t see an easy way to get out of the
situation.

See:
Redirecting to Google Groups https://groups.google.com/forum/#!searchin/ats-lang-users/monad/ats-lang-users/gGOqTJwiegE/K8ieRTSodDEJ

Why not just implement ‘bind’ as a higher order function (as in Haskell)?

On Wednesday, April 1, 2015 at 11:39:20 PM UTC-4, Chotu S wrote:
I have not programmed in ATS for a while , so I was trying to review ATS and tried to implement Maybe monad from this discussion thread :
Redirecting to Google Groups https://groups.google.com/forum/#!searchin/ats-lang-users/monad/ats-lang-users/gGOqTJwiegE/K8ieRTSodDEJ

#include “share/atspre_define.hats”
#include “share/atspre_staload.hats”

datatype Maybe (a : t@ype) =
| Nothing (a) of ()
| Just (a) of (a)

datatype Expr =
| Val of Int
| Div of (Expr , Expr)

(* from UPENN haskell example )
( ok = Div (Div (Val 1972) (Val 2)) (Val 23) *)
val ok = Div (Div ( Val (1972) , Val (2) ) , Val (23))

(* val err = Div (Val 2) (Div (Val 1) (Div (Val 2) (Val 3))) *)
val err = Div (Val (2) , Div (Val (1) , Div (Val (2) , Val (3))))

abst@ype M (t@ype) = ptr

extern
fun {a : t@ype}
ret (v : a ) : M(a)

extern
fun{a,b : t@ype}
bind : M(a) → M(b)

extern
fun{a,b:t@ype}
bind$cont (x : a) : M(b)

assume M (a : t@ype) = Maybe (a)

extern
fun div (m : int , n : int) : Maybe(int)

implement{a}
ret (x) = Just (x)

implement{a,b}
bind (ma) =
case ma of
| Nothing _ => Nothing ()
| Just (x) => bind$cont<a,b> (x)

fun eval (e : Expr) : Maybe(int) =
case e of
| Val n => ret (n)
| Div (e1 , e2) =>
bind<int,int>(eval (e1)) where {
implement bind$cont<int,int> (m) =
bind<int,int>(eval (e2)) where {
implement bind$cont<int,int> (n) = div (m,n) }}

implement
div (m , n) =
if n = 0
then Nothing ()
else ret (m / n)

fun print_maybe (m : Maybe (int)) : void =
case m of
| Nothing _ => println! (“Nothing”)
| Just (x) => println! (x)

implement main0 () = () where {
val res1 = eval (ok)
val res2 = eval (err)
val _ = print_maybe (res1)
val _ = print_maybe (res2)
}

When run this segfaults , and I think it is because it does not see second implementation of bind$cont and keep calling the first one which leads to stack overflow .
Does not second implementation override the first one ?

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3

Here is some explanation:

When the first bind<int,int> is being compiled, ‘bind<int,int>’ is stored
on some
kind of stack. When the second bind<int,int> is countered, the one on the
stack is still
there; so the second bind<int,int> and the first bind<int,int> are actually
compiled into
two calls to the same function (instead of each call to a different
function)On Wednesday, April 1, 2015 at 11:39:20 PM UTC-4, Chotu S wrote:

I have not programmed in ATS for a while , so I was trying to review ATS
and tried to implement Maybe monad from this discussion thread :

Redirecting to Google Groups

#include “share/atspre_define.hats”
#include “share/atspre_staload.hats”

datatype Maybe (a : t@ype) =
| Nothing (a) of ()
| Just (a) of (a)

datatype Expr =
| Val of Int
| Div of (Expr , Expr)

(* from UPENN haskell example )
( ok = Div (Div (Val 1972) (Val 2)) (Val 23) *)
val ok = Div (Div ( Val (1972) , Val (2) ) , Val (23))

(* val err = Div (Val 2) (Div (Val 1) (Div (Val 2) (Val 3))) *)
val err = Div (Val (2) , Div (Val (1) , Div (Val (2) , Val (3))))

abst@ype M (t@ype) = ptr

extern
fun {a : t@ype}
ret (v : a ) : M(a)

extern
fun{a,b : t@ype}
bind : M(a) → M(b)

extern
fun{a,b:t@ype}
bind$cont (x : a) : M(b)

assume M (a : t@ype) = Maybe (a)

extern
fun div (m : int , n : int) : Maybe(int)

implement{a}
ret (x) = Just (x)

implement{a,b}
bind (ma) =
case ma of
| Nothing _ => Nothing ()
| Just (x) => bind$cont<a,b> (x)

fun eval (e : Expr) : Maybe(int) =
case e of
| Val n => ret (n)
| Div (e1 , e2) =>
bind<int,int>(eval (e1)) where {
implement bind$cont<int,int> (m) =
bind<int,int>(eval (e2)) where {
implement bind$cont<int,int> (n) = div (m,n) }}

implement
div (m , n) =
if n = 0
then Nothing ()
else ret (m / n)

fun print_maybe (m : Maybe (int)) : void =
case m of
| Nothing _ => println! (“Nothing”)
| Just (x) => println! (x)

implement main0 () = () where {
val res1 = eval (ok)
val res2 = eval (err)
val _ = print_maybe (res1)
val _ = print_maybe (res2)
}

When run this segfaults , and I think it is because it does not see second
implementation of bind$cont and keep calling the first one which leads to
stack overflow .
Does not second implementation override the first one ?

4

Your assessment of the situation sounds correct to me. However, I don’t see
an easy way to get out of the
situation.

See:
https://groups.google.com/forum/#!searchin/ats-lang-users/monad/ats-lang-users/gGOqTJwiegE/K8ieRTSodDEJ

Why not just implement ‘bind’ as a higher order function (as in Haskell)?On Wednesday, April 1, 2015 at 11:39:20 PM UTC-4, Chotu S wrote:

I have not programmed in ATS for a while , so I was trying to review ATS
and tried to implement Maybe monad from this discussion thread :

Redirecting to Google Groups

#include “share/atspre_define.hats”
#include “share/atspre_staload.hats”

datatype Maybe (a : t@ype) =
| Nothing (a) of ()
| Just (a) of (a)

datatype Expr =
| Val of Int
| Div of (Expr , Expr)

(* from UPENN haskell example )
( ok = Div (Div (Val 1972) (Val 2)) (Val 23) *)
val ok = Div (Div ( Val (1972) , Val (2) ) , Val (23))

(* val err = Div (Val 2) (Div (Val 1) (Div (Val 2) (Val 3))) *)
val err = Div (Val (2) , Div (Val (1) , Div (Val (2) , Val (3))))

abst@ype M (t@ype) = ptr

extern
fun {a : t@ype}
ret (v : a ) : M(a)

extern
fun{a,b : t@ype}
bind : M(a) → M(b)

extern
fun{a,b:t@ype}
bind$cont (x : a) : M(b)

assume M (a : t@ype) = Maybe (a)

extern
fun div (m : int , n : int) : Maybe(int)

implement{a}
ret (x) = Just (x)

implement{a,b}
bind (ma) =
case ma of
| Nothing _ => Nothing ()
| Just (x) => bind$cont<a,b> (x)

fun eval (e : Expr) : Maybe(int) =
case e of
| Val n => ret (n)
| Div (e1 , e2) =>
bind<int,int>(eval (e1)) where {
implement bind$cont<int,int> (m) =
bind<int,int>(eval (e2)) where {
implement bind$cont<int,int> (n) = div (m,n) }}

implement
div (m , n) =
if n = 0
then Nothing ()
else ret (m / n)

fun print_maybe (m : Maybe (int)) : void =
case m of
| Nothing _ => println! (“Nothing”)
| Just (x) => println! (x)

implement main0 () = () where {
val res1 = eval (ok)
val res2 = eval (err)
val _ = print_maybe (res1)
val _ = print_maybe (res2)
}

When run this segfaults , and I think it is because it does not see second
implementation of bind$cont and keep calling the first one which leads to
stack overflow .
Does not second implementation override the first one ?