Data commit

Task/Runtime-evaluation-In-an-environment/Go/runtime-evaluation-in-an-environment.go

@@ -0,0 +1,67 @@
+package main
+
+import (
+    "bitbucket.org/binet/go-eval/pkg/eval"
+    "fmt"
+    "go/parser"
+    "go/token"
+)
+
+func main() {
+    // an expression on x
+    squareExpr := "x*x"
+
+    // parse to abstract syntax tree
+    fset := token.NewFileSet()
+    squareAst, err := parser.ParseExpr(squareExpr)
+    if err != nil {
+        fmt.Println(err)
+        return
+    }
+    // create an environment or "world"
+    w := eval.NewWorld()
+
+    // allocate a variable
+    wVar := new(intV)
+
+    // bind the variable to the name x
+    err = w.DefineVar("x", eval.IntType, wVar)
+    if err != nil {
+        fmt.Println(err)
+        return
+    }
+    // bind the expression AST to the world
+    squareCode, err := w.CompileExpr(fset, squareAst)
+    if err != nil {
+        fmt.Println(err)
+        return
+    }
+    // directly manipulate value of variable within world
+    *wVar = 5
+    // evaluate
+    r0, err := squareCode.Run()
+    if err != nil {
+        fmt.Println(err)
+        return
+    }
+    // change value
+    *wVar--
+    // revaluate
+    r1, err := squareCode.Run()
+    if err != nil {
+        fmt.Println(err)
+        return
+    }
+    // print difference
+    fmt.Println(r0.(eval.IntValue).Get(nil) - r1.(eval.IntValue).Get(nil))
+}
+
+// int value implementation.
+type intV int64
+
+func (v *intV) String() string              { return fmt.Sprint(*v) }
+func (v *intV) Get(*eval.Thread) int64      { return int64(*v) }
+func (v *intV) Set(_ *eval.Thread, x int64) { *v = intV(x) }
+func (v *intV) Assign(t *eval.Thread, o eval.Value) {
+    *v = intV(o.(eval.IntValue).Get(t))
+}