Immutable append/prepend.

expreduce/builtin_list.go

@@ -549,8 +549,9 @@ func GetListDefinitions() (defs []Definition) {
 			if !isExpr {
 				return this
 			}
-			expr.Parts = append(expr.Parts, this.Parts[2])
-			return expr
+			res := NewExpression(append([]Ex{}, expr.Parts...))
+			res.Parts = append(res.Parts, this.Parts[2])
+			return res
 		},
 		SimpleExamples: []TestInstruction{
 			&SameTest{"{a,b,c}", "Append[{a,b},c]"},
@@ -575,8 +576,10 @@ func GetListDefinitions() (defs []Definition) {
 			if !isExpr {
 				return this
 			}
-			expr.Parts = append(append([]Ex{expr.Parts[0]}, this.Parts[2]), expr.Parts[1:]...)
-			return expr
+			res := NewExpression([]Ex{expr.Parts[0]})
+			res.Parts = append(res.Parts, this.Parts[2])
+			res.Parts = append(res.Parts, expr.Parts[1:]...)
+			return res
 		},
 		SimpleExamples: []TestInstruction{
 			&SameTest{"{c,a,b}", "Prepend[{a,b},c]"},

expreduce/ex_expression.go

@@ -9,6 +9,7 @@ import "flag"
 import "hash"
 
 var printevals = flag.Bool("printevals", false, "")
+var checkhashes = flag.Bool("checkhashes", false, "")
 
 type Expression struct {
 	Parts []Ex
@@ -104,6 +105,7 @@ func (this *Expression) mergeSequences(es *EvalState, headStr string, shouldEval
 
 func (this *Expression) Eval(es *EvalState) Ex {
 	lastExHash := uint64(0)
+	var lastEx Ex = this
 	currExHash := hashEx(this)
 	if currExHash == this.cachedHash {
 		return this
@@ -113,6 +115,12 @@ func (this *Expression) Eval(es *EvalState) Ex {
 	for currExHash != lastExHash {
 		lastExHash = currExHash
 		curr, isExpr := currEx.(*Expression)
+		if *checkhashes {
+			if isExpr && curr.cachedHash != 0 && currExHash != curr.cachedHash {
+				fmt.Printf("invalid cache: %v. Used to be %v\n", curr, lastEx)
+			}
+			lastEx = currEx
+		}
 
 		if isExpr && insideDefinition {
 			retVal, isReturn := tryReturnValue(curr)