From 0929ef05f926bfaa6697e211e341b532fab89d5f Mon Sep 17 00:00:00 2001
From: Enrico Lumetti <enrico.lumetti@gmail.com>
Date: Sun, 1 May 2022 15:37:44 +0200
Subject: [PATCH] Add CVar language and interpreter

---
 cvar.rkt      | 38 ++++++++++++++++++++++++++++++++++++++
 rvar.rkt      |  4 ++--
 test-cvar.rkt | 39 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 79 insertions(+), 2 deletions(-)
 create mode 100644 cvar.rkt
 create mode 100644 test-cvar.rkt

diff --git a/cvar.rkt b/cvar.rkt
new file mode 100644
index 0000000..316e7ab
--- /dev/null
+++ b/cvar.rkt
@@ -0,0 +1,38 @@
+#lang racket
+
+(provide Int Prim Var Assign Seq Return CProgram interp-CVar% interp-CVar)
+
+(require "rvar.rkt")
+(require racket/dict)
+(require racket/struct)
+
+(struct CProgram (info labeled-seq) #:transparent)
+
+(struct Assign (var exp) #:transparent)
+(struct Seq (stmt tail) #:transparent)
+(struct Return (exp) #:transparent)
+
+(define interp-CVar%
+    (class interp-RVar-class
+       (super-new)
+           
+       (define/public ((interp-stmt env) stmt)
+         (match stmt
+           [(Assign (Var varname) exp)
+            (let ([val ((send this interp-exp env) exp)])
+                 (dict-set! env varname val))]))
+
+       (define/public ((interp-seq env) seq)
+         (match seq
+           [(Seq stmt tail)
+            (begin
+             ((interp-stmt env) stmt)
+             ((interp-seq env) tail))]
+           [(Return exp) ((send this interp-exp env) exp)]))
+
+       (define/public (interp-cprogram program)
+          (match program
+            [(CProgram _ labeled-seq) ((interp-seq (make-hash)) (cdar labeled-seq))]))))
+
+(define (interp-CVar program)
+  (send (new interp-CVar%) interp-cprogram program))
diff --git a/rvar.rkt b/rvar.rkt
index 94c5d82..b144363 100644
--- a/rvar.rkt
+++ b/rvar.rkt
@@ -1,11 +1,11 @@
 #lang racket
 
+(provide Int Prim Var Let Program interp-RVar-class interp-RVar)
+
 (require racket/fixnum)
 (require racket/dict)
 (require racket/struct)
 
-(provide Int Prim Var Let Program interp-RVar-class interp-RVar)
-
 (struct Int (value) #:transparent)
 (struct Var (name) #:transparent)
 (struct Prim (op args) #:transparent)
diff --git a/test-cvar.rkt b/test-cvar.rkt
new file mode 100644
index 0000000..d2c43f4
--- /dev/null
+++ b/test-cvar.rkt
@@ -0,0 +1,39 @@
+#lang racket
+
+(require "test-util.rkt")
+(require "cvar.rkt")
+
+(define seq-1
+    (Return (Int 0)))
+
+(define seq-2
+    (Seq (Assign (Var 'x) (Int 42))
+     (Return (Int 42))))
+
+(define seq-3
+    (Seq (Assign (Var 'x) (Int 42))
+     (Return (Prim '+ (list (Int 1) (Var 'x))))))
+
+(define seq-4
+    (Return (Prim 'read '())))
+
+(define (make-start-seq seq)
+    (CProgram '() `((start . ,seq))))
+
+(test-eq
+   (interp-CVar (make-start-seq seq-1))
+   0)
+
+(test-eq
+   (interp-CVar (make-start-seq seq-2))
+   42)
+
+(test-eq
+   (interp-CVar (make-start-seq seq-3))
+   43)
+
+(with-input-from-num-list '(21)
+ (lambda ()
+  (test-eq
+     (interp-CVar (make-start-seq seq-4))
+     21)))