Add ConstExpr

Author: antonmedv

bench_test.go

@@ -147,6 +147,29 @@ func Benchmark_callFast(b *testing.B) {
 	}
 }
 
+func Benchmark_callConstExpr(b *testing.B) {
+	env := map[string]interface{}{
+		"Fn": func(s ...interface{}) interface{} { return s[0].(string)+s[1].(string) == s[2].(string) },
+	}
+
+	program, err := expr.Compile(`Fn("a", "b", "ab")`, expr.Env(env), expr.ConstExpr("Fn"))
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	var out interface{}
+	for n := 0; n < b.N; n++ {
+		out, err = vm.Run(program, env)
+	}
+
+	if err != nil {
+		b.Fatal(err)
+	}
+	if !out.(bool) {
+		b.Fail()
+	}
+}
+
 func Benchmark_largeStructAccess(b *testing.B) {
 	type Env struct {
 		Data  [1024 * 1024 * 10]byte

cmd/exe/debugger.go

@@ -25,7 +25,8 @@ func debugger() {
 	check(err)
 
 	if opt {
-		optimizer.Optimize(&tree.Node)
+		err = optimizer.Optimize(&tree.Node, nil)
+		check(err)
 	}
 
 	program, err := compiler.Compile(tree, nil)

cmd/exe/main.go

@@ -91,7 +91,8 @@ func printAst() {
 		check(err)
 
 		if opt {
-			optimizer.Optimize(&tree.Node)
+			err = optimizer.Optimize(&tree.Node, nil)
+			check(err)
 		}
 	}
 
@@ -111,7 +112,8 @@ func printDisassemble() {
 		check(err)
 
 		if opt {
-			optimizer.Optimize(&tree.Node)
+			err = optimizer.Optimize(&tree.Node, nil)
+			check(err)
 		}
 	}
 
@@ -130,7 +132,8 @@ func runProgram() {
 		check(err)
 
 		if opt {
-			optimizer.Optimize(&tree.Node)
+			err = optimizer.Optimize(&tree.Node, nil)
+			check(err)
 		}
 	}
 

compiler/compiler.go

@@ -24,6 +24,7 @@ func Compile(tree *parser.Tree, config *conf.Config) (program *Program, err erro
 		index:     make(map[interface{}]uint16),
 		locations: make(map[int]file.Location),
 	}
+
 	if config != nil {
 		c.mapEnv = config.MapEnv
 		c.cast = config.Expect

checker/patcher.go renamed to compiler/patcher.go

@@ -1,9 +1,8 @@
-package checker
+package compiler
 
 import (
 	"github.com/antonmedv/expr/ast"
 	"github.com/antonmedv/expr/internal/conf"
-	"github.com/antonmedv/expr/parser"
 )
 
 type operatorPatcher struct {
@@ -38,10 +37,10 @@ func (p *operatorPatcher) Exit(node *ast.Node) {
 	}
 }
 
-func PatchOperators(tree *parser.Tree, config *conf.Config) {
+func PatchOperators(node *ast.Node, config *conf.Config) {
 	if len(config.Operators) == 0 {
 		return
 	}
 	patcher := &operatorPatcher{ops: config.Operators, types: config.Types}
-	ast.Walk(&tree.Node, patcher)
+	ast.Walk(node, patcher)
 }

docs/Optimizations.md

@@ -61,3 +61,18 @@ Will be replaced with binary operator:
 ```
 
 Ranges computed on compile stage, repleced with preallocated slices.
+
+## Const expr
+
+If some function marked as constant expression with `expr.ConstExpr`. It will be replaced with result
+of call, if all arguments are constants.
+
+```go
+expr.ConstExpt("fib")
+```
+
+```js
+fib(42)
+``` 
+
+Will be replaced with result of `fib(42)` on compile step. No need to calculate it during runtime.

docs/Usage.md

@@ -199,3 +199,34 @@ func main() {
 	fmt.Printf("%v", visitor.identifiers)  // outputs [foo bar]
 }
 ```
+
+## ConstExpr
+
+Expr has support for constant expression evaluation during compile time. 
+
+```go
+func fib(n int) int {
+	if n <= 1 {
+		return n
+	}
+	return fib(n-1) + fib(n-2)
+}
+
+code := `[fib(5), fib(3+3), fib(dyn)]`
+
+env := map[string]interface{}{
+	"fib": fib,
+	"dyn": 0,
+}
+
+options := []expr.Option{
+	expr.Env(env),
+	expr.ConstExpr("fib"), // Mark fib func as constant expression.
+}
+
+program, err := expr.Compile(code, options...)
+```
+
+Only `fib(5)` and `fib(6)` calculated on Compile, `fib(dyn)` can be called at runtime.
+
+Resulting program will be equal to `[5, 8, fib(dyn)]`.

expr.go

@@ -2,6 +2,7 @@ package expr
 
 import (
 	"fmt"
+	"github.com/antonmedv/expr/file"
 	"reflect"
 
 	"github.com/antonmedv/expr/checker"
@@ -44,17 +45,18 @@ func Eval(input string, env interface{}) (interface{}, error) {
 // as well as all fields of embedded structs and struct itself.
 // If map is passed, all items will be treated as variables.
 // Methods defined on this type will be available as functions.
-func Env(i interface{}) Option {
+func Env(env interface{}) Option {
 	return func(c *conf.Config) {
-		if _, ok := i.(map[string]interface{}); ok {
+		if _, ok := env.(map[string]interface{}); ok {
 			c.MapEnv = true
 		} else {
-			if reflect.ValueOf(i).Kind() == reflect.Map {
-				c.DefaultType = reflect.TypeOf(i).Elem()
+			if reflect.ValueOf(env).Kind() == reflect.Map {
+				c.DefaultType = reflect.TypeOf(env).Elem()
 			}
 		}
 		c.Strict = true
-		c.Types = conf.CreateTypesTable(i)
+		c.Types = conf.CreateTypesTable(env)
+		c.Env = env
 	}
 }
 
@@ -75,6 +77,14 @@ func Operator(operator string, fn ...string) Option {
 	}
 }
 
+// ConstExpr defines func expression as constant. If all argument to this function is constants,
+// then it can be replaced by result of this func call on compile step.
+func ConstExpr(fn string) Option {
+	return func(c *conf.Config) {
+		c.ConstExpr(fn)
+	}
+}
+
 // AsBool tells the compiler to expect boolean result.
 func AsBool() Option {
 	return func(c *conf.Config) {
@@ -106,8 +116,9 @@ func Optimize(b bool) Option {
 // Compile parses and compiles given input expression to bytecode program.
 func Compile(input string, ops ...Option) (*vm.Program, error) {
 	config := &conf.Config{
-		Operators: make(map[string][]string),
-		Optimize:  true,
+		Operators:    make(map[string][]string),
+		ConstExprFns: make(map[string]reflect.Value),
+		Optimize:     true,
 	}
 
 	for _, op := range ops {
@@ -127,10 +138,18 @@ func Compile(input string, ops ...Option) (*vm.Program, error) {
 	if err != nil {
 		return nil, err
 	}
-	checker.PatchOperators(tree, config)
+
+	// Patch operators before Optimize, as we may also mark it as ConstExpr.
+	compiler.PatchOperators(&tree.Node, config)
 
 	if config.Optimize {
-		optimizer.Optimize(&tree.Node)
+		err = optimizer.Optimize(&tree.Node, config)
+		if err != nil {
+			if fileError, ok := err.(*file.Error); ok {
+				return nil, fmt.Errorf("%v", fileError.Format(tree.Source))
+			}
+			return nil, err
+		}
 	}
 
 	program, err := compiler.Compile(tree, config)

expr_test.go

@@ -234,6 +234,46 @@ func ExampleOperator() {
 	// Output: true
 }
 
+func fib(n int) int {
+	if n <= 1 {
+		return n
+	}
+	return fib(n-1) + fib(n-2)
+}
+
+func ExampleConstExpr() {
+	code := `[fib(5), fib(3+3), fib(dyn)]`
+
+	env := map[string]interface{}{
+		"fib": fib,
+		"dyn": 0,
+	}
+
+	options := []expr.Option{
+		expr.Env(env),
+		expr.ConstExpr("fib"), // Mark fib func as constant expression.
+	}
+
+	program, err := expr.Compile(code, options...)
+	if err != nil {
+		fmt.Printf("%v", err)
+		return
+	}
+
+	// Only fib(5) and fib(6) calculated on Compile, fib(dyn) can be called at runtime.
+	env["dyn"] = 7
+
+	output, err := expr.Run(program, env)
+	if err != nil {
+		fmt.Printf("%v", err)
+		return
+	}
+
+	fmt.Printf("%v\n", output)
+
+	// Output: [5 8 13]
+}
+
 func ExampleAllowUndefinedVariables() {
 	code := `name == nil ? "Hello, world!" : sprintf("Hello, %v!", name)`
 
@@ -866,6 +906,43 @@ func TestExpr_calls_with_nil(t *testing.T) {
 	require.Equal(t, true, out)
 }
 
+func TestConstExpr_error(t *testing.T) {
+	env := map[string]interface{}{
+		"divide": func(a, b int) int { return a / b },
+	}
+
+	_, err := expr.Compile(
+		`1 + divide(1, 0)`,
+		expr.Env(env),
+		expr.ConstExpr("divide"),
+	)
+	require.Error(t, err)
+	require.Equal(t, "compile error: integer divide by zero (1:5)\n | 1 + divide(1, 0)\n | ....^", err.Error())
+}
+
+func TestConstExpr_error_wrong_type(t *testing.T) {
+	env := map[string]interface{}{
+		"divide": 0,
+	}
+
+	_, err := expr.Compile(
+		`1 + divide(1, 0)`,
+		expr.Env(env),
+		expr.ConstExpr("divide"),
+	)
+	require.Error(t, err)
+	require.Equal(t, "const expression \"divide\" must be a function", err.Error())
+}
+
+func TestConstExpr_error_no_env(t *testing.T) {
+	_, err := expr.Compile(
+		`1 + divide(1, 0)`,
+		expr.ConstExpr("divide"),
+	)
+	require.Error(t, err)
+	require.Equal(t, "no environment for const expression: divide", err.Error())
+}
+
 //
 // Mock types
 //