支持 可选参数自定义函数的注册

README.md

@@ -46,8 +46,8 @@
 | `round(x)`  | 四舍五入取整                 | round(4.4) = 4, round(4.5) = 5        |
 | `sqrt(x)`   | 平方根，square root          | sqrt(4) = 2                           |
 | `cbrt(x)`   | 立方根，cube root            | cbrt(27) = 3                          |
-| `max(x, y)` | x, y 中的较大值              | max(2, 3) = 3                         |
-| `min(x, y)` | x, y 中的较小值              | min(2, 3) = 2                         |
+| `max(x, ...)` | 参数中的较大值              | max(1)=1,max(2,3)=3,max(4,8,6,8,10)=10 |
+| `min(x, ...)` | 参数中的较小值              | min(1)=1,min(2,3)=2,max(4,8,6,8,10)=4 |
 | `noerr(x)`  | 计算 x 出错时返回 0          | noerr(1 / 1)  = 1, noerr( 1/ 0 ) = 0  |
 | `double(x)`  | 返回 x 的双倍值，这是一个自定义的函数示例，你可以注册任意的自定义函数到引擎中  | double(6) = 12  |
 
@@ -154,10 +154,10 @@ e.g
   // RegFunction is Top level function
   // the same function name only needs to be registered once.
   // double is register function name.
-  // 1 is a number of parameter signatures.
+  // 1 is a number of parameter signatures. should be -1, 0, or a positive integer
   // func(expr ...engine.ExprAST) float64 is your function.
   engine.RegFunction("double", 1, func(expr ...engine.ExprAST) float64 {
-    // you can use the index value directly according to the number of parameters
+    // when argc > 0，you can use the index value directly according to the number of parameters
     // without worrying about crossing the boundary.
     // use ExprASTResult to get the result of the ExprAST structure.
     return engine.ExprASTResult(expr[0]) * 2
@@ -178,7 +178,8 @@ fmt.Printf("double(6) + 2 = %f\n", r) // will print ： double(6) + 2 = 14.00000
 注意事项：
 - 注册的函数名只能是英文字母和数字，且必须英文字母开头（区分大小写）;
 - 每一个函数名只能且只需注册一次；
-- 注册的函数逻辑中如果有 panic ，需要程序自己捕获处理;
+- 注册的函数逻辑中如果有 panic ，需要程序自己捕获处理;  
+- argc=-1，即该函数的参数是可变的，expr 的长度需要开发者自行逻辑判断处理；
 
 ## Compile    
 

engine/util.go

@@ -63,15 +63,19 @@ func Float64ToStr(f float64) string {
 
 // RegFunction is Top level function
 // register a new function to use in expressions
+// name: be register function name. the same function name only needs to be registered once.
+// argc: this is a number of parameter signatures. should be -1, 0, or a positive integer
+//       -1 variable-length argument; >=0 fixed numbers argument
+// fun:  function handler
 func RegFunction(name string, argc int, fun func(...ExprAST) float64) error {
 	if len(name) == 0 {
-		return errors.New("RegFunction name is not empty.")
+		return errors.New("RegFunction name is not empty")
 	}
-	if argc < 1 {
-		return errors.New("RegFunction argc is must has one arg at least.")
+	if argc < -1 {
+		return errors.New("RegFunction argc should be -1, 0, or a positive integer")
 	}
 	if _, ok := defFunc[name]; ok {
-		return errors.New("RegFunction name is already exist.")
+		return errors.New("RegFunction name is already exist")
 	}
 	defFunc[name] = defS{argc, fun}
 	return nil

engine/util_test.go

@@ -1,6 +1,10 @@
 package engine
 
-import "testing"
+import (
+	"math/rand"
+	"testing"
+	"time"
+)
 
 func TestParseAndExecSimple(t *testing.T) {
 	type U struct {
@@ -144,11 +148,35 @@ func TestRegFunction(t *testing.T) {
 			"percentage50(6)",
 			3,
 		},
+		{
+			"range",
+			0,
+			func(expr ...ExprAST) float64 {
+				return 10.0
+			},
+			"range()",
+			10,
+		},
+		{
+			"choice",
+			-1,
+			func(expr ...ExprAST) float64 {
+				rand.Seed(time.Now().UnixNano())
+				return ExprASTResult(expr[rand.Intn(len(expr))])
+			},
+			"choice(1.1, 9.8, 2.5, 100)",
+			10,
+		},
 	}
 	for _, f := range funs {
 		_ = RegFunction(f.Name, f.Argc, f.Fun)
 		r, err := ParseAndExec(f.Exp)
-		if r != f.R {
+		if f.Name == "choice" {
+			if !inSlices(r, []float64{1.1, 9.8, 2.5, 100}) {
+				t.Error(err, "RegFunction errors when register new function: ", f.Name)
+			}
+			continue
+		} else if r != f.R {
 			t.Error(err, "RegFunction errors when register new function: ", f.Name)
 		}
 	}
@@ -194,3 +222,12 @@ func TestParseAndExecError(t *testing.T) {
 		}
 	}
 }
+
+func inSlices(target float64, s []float64) bool {
+	for _, v := range s {
+		if v == target {
+			return true
+		}
+	}
+	return false
+}