Testing

src/DSL.ml

@@ -1,49 +0,0 @@
-(*
-open Expr
-
-(* read x; 
-   read y; 
-   z = y*y; 
-   write (x+z) 
-*)
-let t = 
-  Seq (
-    Read "x", 
-    Seq (
-      Read "y", 
-      Seq (
-        Assign ("z", Mul (Var "y", Var "y")), 
-        Write (Add (Var "x", Var "z"))
-      )
-    )
-  )
-    
-let _ = match run [2; 3] t with [result] -> Printf.printf "Result: %d\n" result
-let _ = try ignore (run [2] t) with Failure s -> Printf.printf "Error: %s\n" s
-    
-let ( ! ) x = Var x
-let ( % ) n = Const n
-let ( + ) e1 e2 = Add (e1, e2)
-let ( * ) e1 e2 = Mul (e1, e2)
-    
-let skip         = Skip
-let (:=) x e     = Assign (x, e)
-let read   x     = Read x
-let write  e     = Write e
-let (|>)   s1 s2 = Seq (s1, s2)
-    
-let t = 
-  read "x" |> 
-  read "y" |> 
-  ("z" := !"y" * !"y") |> 
-  write (!"x" + !"z")
-    
-let _ = match run [2; 3] t with [result] -> Printf.printf "Result: %d\n" result
-let _ = try ignore (run [2] t) with Failure s -> Printf.printf "Error: %s\n" s
-
-let run input stmt = srun input (compile_stmt stmt)
-
-let _ = match run [2; 3] t with [result] -> Printf.printf "Result: %d\n" result
-let _ = try ignore (run [2] t) with Failure s -> Printf.printf "Error: %s\n" s
-
- *)

src/Embedding.ml

@@ -0,0 +1,40 @@
+(* A deep embedding of simple expressions in OCaml. *)
+
+(* Opening GT yet again. *)
+open GT
+       
+(* Opening the substrate module for convenience. *)
+open Expr
+
+(* Shortcuts for leaf constructors *)
+let ( ! ) x = Var x
+let ( !? ) n = Const n
+
+(* Implementation of operators *)
+let binop op x y = Binop (op, x, y)
+                         
+let ( +  ) = binop "+"
+let ( -  ) = binop "-"
+let ( *  ) = binop "*"
+let ( /  ) = binop "/"
+let ( %  ) = binop "%"
+let ( <  ) = binop "<"
+let ( <= ) = binop "<="
+let ( >  ) = binop ">"
+let ( >= ) = binop ">="
+let ( == ) = binop "=="
+let ( != ) = binop "!="
+let ( && ) = binop "&&"
+let ( || ) = binop "!!"
+
+(* Some predefined names for variables *)
+let x = !"x"
+let y = !"y"
+let z = !"z"
+let t = !"t"
+
+(* Voila; comment this out before submitting the solution *)
+let _ =
+  List.iter (fun e -> Printf.printf "eval s (%s) = %d\n" (show(expr) e) (eval s e)) [x+y*z- !?3; t-z+y && x]
+
+                   

src/Expr.ml

@@ -1,10 +1,12 @@
+(* Simple expressions: syntax and semantics *)
+
 (* Opening a library for generic programming (https://github.com/dboulytchev/GT).
-   The library provides "@type ..." syntax extension and plugins like show, gmap, etc.
+   The library provides "@type ..." syntax extension and plugins like show, etc.
 *)
 open GT 
              
-(* The type for the expression. Note, in regular OCaml there is no "@type..." notation, 
-   it came from GT. *)
+(* The type for the expression. Note, in regular OCaml there is no "@type..." 
+   notation, it came from GT. *)
 @type expr =
   (* integer constant *) | Const of int
   (* variable         *) | Var   of string
@@ -24,22 +26,28 @@ type state = string -> int
 (* Empty state: maps every variable into nothing. *)
 let empty = fun x -> failwith (Printf.sprintf "Undefined variable %s" x)
 
-(* Update: non-destructively "modifies" the state s by binding the variable x to value v and 
-   returns the new state.
+(* Update: non-destructively "modifies" the state s by binding the variable x 
+   to value v and returns the new state.
 *)
 let update x v s = fun y -> if x = y then v else s y
 
 (* An example of a non-trivial state: *)                                                   
 let s = update "x" 1 @@ update "y" 2 @@ update "z" 3 @@ update "t" 4 empty
 
-(* Some testing *)
+(* Some testing; comment this definition out when submitting the solution. *)
 let _ =
   List.iter
     (fun x ->
        try  Printf.printf "%s=%d\n" x @@ s x
        with Failure s -> Printf.printf "%s\n" s
     ) ["x"; "a"; "y"; "z"; "t"; "b"]
-  
-  
-                                                                 
-                
+
+(* Expression evaluator
+
+     val eval : state -> expr -> int
+ 
+   Takes a state and an expression, andreturns the value of the expression in 
+   the given state.
+*)
+let eval = failwith "Not implemented yet"
+                    

src/Makefile

@@ -2,7 +2,7 @@ TOPFILE = rc
 OCAMLC = ocamlc
 OCAMLOPT = ocamlopt
 OCAMLDEP = ocamldep
-SOURCES = $(wildcard *.ml)
+SOURCES = Expr.ml Embedding.ml
 LIBS = GT.cma unix.cma re.cma re_emacs.cma re_str.cma
 CAMLP5 = -pp "camlp5o -I `ocamlfind -query GT.syntax` -I `ocamlfind -query ostap.syntax` pa_ostap.cmo pa_gt.cmo -L `ocamlfind -query GT.syntax`"
 PXFLAGS = $(CAMLP5)