pkg/eval: Refactor the argument parsing logic of randint.

pkg/eval/builtin_fn_num.go

@@ -348,43 +348,39 @@ func randint(args ...vals.Num) (vals.Num, error) {
 		return -1, errs.ArityMismatch{What: "arguments",
 			ValidLow: 1, ValidHigh: 2, Actual: len(args)}
 	}
-	allInt := true
 	for _, arg := range args {
 		if err := checkExactIntArg(arg); err != nil {
 			return nil, err
 		}
-		if _, ok := arg.(*big.Int); ok {
-			allInt = false
-		}
-	}
-	if allInt {
-		var low, high int
-		if len(args) == 1 {
-			low, high = 0, args[0].(int)
-		} else {
-			low, high = args[0].(int), args[1].(int)
-		}
-		if high <= low {
-			return 0, errs.BadValue{What: "high value",
-				Valid: fmt.Sprint("larger than ", low), Actual: strconv.Itoa(high)}
-		}
-		x := withRand(func(r *rand.Rand) int { return r.Intn(high - low) })
-		return low + x, nil
 	}
-	var low, high *big.Int
 	if len(args) == 1 {
-		low, high = big.NewInt(0), args[0].(*big.Int)
-	} else {
-		var casted_args [2]*big.Int
-		for i, arg := range args {
-			if casted_arg, ok := arg.(*big.Int); ok {
-				casted_args[i] = casted_arg
-			} else {
-				casted_args[i] = big.NewInt(int64(arg.(int)))
+		if high, ok := args[0].(int); ok {
+			return randIntSmallInt(0, high)
+		} else { // *big.Int
+			return randIntBigInt(&big.Int{}, args[0].(*big.Int))
+		}
+	} else { // len(args) == 2
+		if low, ok := args[0].(int); ok {
+			if high, ok := args[1].(int); ok {
+				return randIntSmallInt(low, high)
 			}
 		}
-		low, high = casted_args[0], casted_args[1]
+		// One or both of low and high is *big.Int
+		return randIntBigInt(
+			vals.PromoteToBigInt(args[0]), vals.PromoteToBigInt(args[1]))
 	}
+}
+
+func randIntSmallInt(low, high int) (vals.Num, error) {
+	if high <= low {
+		return 0, errs.BadValue{What: "high value",
+			Valid: fmt.Sprint("larger than ", low), Actual: strconv.Itoa(high)}
+	}
+	x := withRand(func(r *rand.Rand) int { return r.Intn(high - low) })
+	return low + x, nil
+}
+
+func randIntBigInt(low, high *big.Int) (vals.Num, error) {
 	if high.Cmp(low) <= 0 {
 		return 0, errs.BadValue{What: "high value",
 			Valid: fmt.Sprint("larger than ", low), Actual: high.String()}

pkg/eval/builtin_fn_num_test.elvts

@@ -411,6 +411,21 @@ Exception: arity mismatch: arguments must be 1 to 2 values, but is 3 values
 Exception: bad value: argument must be exact integer, but is (num 1.0)
   [tty]:1:1-11: randint 1.0
 
+## mixed argument type ##
+// Regression test for https://b.elv.sh/1856.
+~> var bound = 100000000000000000000000000
+   var x = (randint 0 $bound)
+   and (<= 0 $x) (< $x $bound)
+▶ $true
+~> var bound = 100000000000000000000000000
+   var x = (randint -$bound $bound)
+   and (<= -$bound $x) (< $x $bound)
+▶ $true
+~> var bound = 100000000000000000000000000
+   var x = (randint -$bound 0)
+   and (<= -$bound $x) (< $x 0)
+▶ $true
+
 /////////////
 # -randseed #
 /////////////
@@ -614,22 +629,3 @@ Exception: bad value: step must be negative, but is 0.5
 ~> range 1.2 >&-
 Exception: port does not support value output
   [tty]:1:1-13: range 1.2 >&-
-
-## randint big arguments mixed ##
-~> var bound = 100000000000000000000000000
-   var x = (randint $bound)
-   and (<= 0 $x) (< $x $bound)
-▶ $true
-~> var bound = 100000000000000000000000000
-   var x = (randint 0 $bound)
-   and (<= 0 $x) (< $x $bound)
-▶ $true
-~> var bound = 100000000000000000000000000
-   var x = (randint -$bound $bound)
-   and (<= -$bound $x) (< $x $bound)
-▶ $true
-~> var bound = 100000000000000000000000000
-   var x = (randint -$bound 0)
-   and (<= -$bound $x) (< $x 0)
-▶ $true
-