Add self() for anonymous function recursion (#83)

* Add self() for anonymous function recursion

* use self() in a couple of examples, add a todo

* update readme a bit

* update readme example

README.md

@@ -29,30 +29,37 @@ Or get one of the [binary releases](https://github.com/grol-io/grol/releases)
 ## What it does
 Sample:
 ```go
-gorepl -parse
-$ fact = func(n) {if (n<=1) {return 1} n*fact(n-1)}
+$ grol -parse
+10:53:12.675 grol 0.29.0 go1.22.5 arm64 darwin - welcome!
+$ fact = func(n) {if (n<=1) {return 1} n*self(n-1)} // could be n*fact(n-1) too
+== Parse ==> fact = func(n) {
+	if n <= 1 {
+		return 1
+	}
+	n * self(n - 1)
+}
 $ n=fact(6)
-== Parse ==> (n = fact(6))
+== Parse ==> n = fact(6)
 == Eval  ==> 720
 $ m=fact(7)
-== Parse ==> (m = fact(7))
+== Parse ==> m = fact(7)
 == Eval  ==> 5040
 $ m/n
-== Parse ==> (m / n)
+== Parse ==> m / n
 == Eval  ==> 7
 ```
 
 ## Language features
 
 Functional int, float, string and boolean expressions
 
-Functions, lambdas, closures
+Functions, lambdas, closures (including recursion in anonymous functions, using `self()`)
 
-Arrays, maps,
+Arrays, maps
 
 print, log
 
-macros and more all the time
+macros and more all the time (like canonical reformat using `grol -format` and wasm/online version etc)
 
 See also [sample.gr](examples/sample.gr) and others in that folder, that you can run with
 ```

eval/eval.go

@@ -345,7 +345,9 @@ func extendFunctionEnv(name string, fn object.Function, args []object.Object) (*
 	for paramIdx, param := range fn.Parameters {
 		env.Set(param.Value().Literal(), args[paramIdx])
 	}
-
+	// for recursion in anonymous functions.
+	// TODO: consider not having to keep setting this in the function's env and treating as a keyword.
+	env.Set("self", fn)
 	return env, nil
 }
 

eval/eval_test.go

@@ -47,6 +47,14 @@ func TestEvalIntegerExpression(t *testing.T) {
 		{`a=2; b=3; r=a+5*(b++)+b;`, 21}, // left to right eval, yet not that not well defined behavior.
 		{`a=2; b=3; r=b+5*(b++)+a;`, 20}, // because that solo b is evaluated last, after the b++ - not well defined behavior.
 		{`a=2; b=3; r=a+5*b+++b;`, 21},   // parentheses are not technically needed here though... this is rather un readable.
+		{`// IIFE factorial
+func(n) {
+	if n <= 1 {
+		return 1
+	}
+	n * self(n - 1)
+}(5)
+`, 120},
 	}
 
 	for i, tt := range tests {

examples/anon.gr

@@ -0,0 +1,11 @@
+/*
+ Anonymous function recursion
+ Define and immediately call factorial
+ (IIFE: Immediately Invoked Function Expression)
+ */
+ func(n) {
+	if n <= 1 {
+		return 1
+	}
+	n * self(n - 1)
+}(5) // will return 120

examples/pi2.gr

@@ -2,12 +2,12 @@
  Γ(x + 1/2) ~ Γ(x)x^(1/2) = (x-1)!√x
  Γ(x + 1/2) = (2x - 1)!! * 2^-x * √π
 */
-f=func(i,n, prod) {
-    //log(i, prod)
-	if (i==n+1) {
-        return 1./(prod*prod*n)
-    }
-    f(i+1, n, prod * ( 1 - 1./(2*i)))
+f = func(i, n, prod) {
+	//log(i, prod)
+	if i == n+1 {
+		return 1. / (prod * prod * n)
+	}
+	self(i+1, n, prod*(1-1./(2*i)))
 }
-n=200000
-f(1,n,1)
+n = 200000
+f(1, n, 1)

examples/sample.gr

@@ -18,7 +18,7 @@ fact=func(n) { // function
     if (n<=1) {
         return 1
     }
-    /* recursion: */ n*fact(n-1) // also last evaluated expression is returned (ie return at the end is optional)
+    /* recursion: */ n*self(n-1) // also last evaluated expression is returned (ie return at the end is optional)
 }
 
 a=[fact(5), "abc", 76-3] // array can contain different types