Added the while loop

_docs/mod/core.md

@@ -190,3 +190,13 @@ set! NAME VALUE
 
 Sets the value of variable NAME to VALUE. VALUE must be non-null otherwise `set!` will raise an error.
 
+### while
+
+```
+while [GUARD] BLOCK
+```
+
+Iterate over BLOCK while GUARD is true.  If GUARD is not included, `while` will loop indefinitely.
+
+BLOCK can call `break` and `continue` which will exit out of the loop, or jump to the start of the next iteration
+respectively. The return value of `while` will be nil, unless `break` is called with a value.

ucl/builtins.go

@@ -1039,7 +1039,7 @@ func foreachBuiltin(ctx context.Context, args macroArgs) (Object, error) {
 		l := t.Len()
 		for i := 0; i < l; i++ {
 			v := t.Index(i)
-			last, err = args.evalBlock(ctx, blockIdx, []Object{v}, true) // TO INCLUDE: the index
+			last, err = args.evalBlock(ctx, blockIdx, []Object{v}, false) // TO INCLUDE: the index
 			if err != nil {
 				if errors.As(err, &breakErr) {
 					if !breakErr.isCont {
@@ -1052,7 +1052,7 @@ func foreachBuiltin(ctx context.Context, args macroArgs) (Object, error) {
 		}
 	case Hashable:
 		err := t.Each(func(k string, v Object) error {
-			last, err = args.evalBlock(ctx, blockIdx, []Object{StringObject(k), v}, true)
+			last, err = args.evalBlock(ctx, blockIdx, []Object{StringObject(k), v}, false)
 			return err
 		})
 		if errors.As(err, &breakErr) {
@@ -1069,7 +1069,7 @@ func foreachBuiltin(ctx context.Context, args macroArgs) (Object, error) {
 				return nil, err
 			}
 
-			last, err = args.evalBlock(ctx, blockIdx, []Object{v}, true) // TO INCLUDE: the index
+			last, err = args.evalBlock(ctx, blockIdx, []Object{v}, false) // TO INCLUDE: the index
 			if err != nil {
 				if errors.As(err, &breakErr) {
 					if !breakErr.isCont {
@@ -1086,6 +1086,42 @@ func foreachBuiltin(ctx context.Context, args macroArgs) (Object, error) {
 	return last, nil
 }
 
+func whileBuiltin(ctx context.Context, args macroArgs) (Object, error) {
+	blockIdx := 1
+	loopForever := false
+
+	if args.nargs() < 2 {
+		blockIdx = 0
+		loopForever = true
+	}
+
+	var (
+		breakErr errBreak
+	)
+
+	for {
+		if !loopForever {
+			guard, err := args.evalArg(ctx, 0)
+			if err != nil {
+				return nil, err
+			}
+			if !isTruthy(guard) {
+				return nil, nil
+			}
+		}
+
+		if _, err := args.evalBlock(ctx, blockIdx, nil, false); err != nil {
+			if errors.As(err, &breakErr) {
+				if !breakErr.isCont {
+					return breakErr.ret, nil
+				}
+			} else {
+				return nil, err
+			}
+		}
+	}
+}
+
 func errorBuiltin(ctx context.Context, args invocationArgs) (Object, error) {
 	if len(args.args) < 1 {
 		return nil, errors.New("need at least one arguments")

ucl/inst.go

@@ -105,6 +105,7 @@ func New(opts ...InstOption) *Inst {
 
 	rootEC.addMacro("if", macroFunc(ifBuiltin))
 	rootEC.addMacro("for", macroFunc(foreachBuiltin))
+	rootEC.addMacro("while", macroFunc(whileBuiltin))
 	rootEC.addMacro("proc", macroFunc(procBuiltin))
 	rootEC.addMacro("try", macroFunc(tryBuiltin))
 

ucl/testbuiltins_test.go

@@ -466,6 +466,76 @@ func TestBuiltins_For(t *testing.T) {
 	}
 }
 
+func TestBuiltins_While(t *testing.T) {
+	tests := []struct {
+		desc string
+		expr string
+		want string
+	}{
+		{desc: "iterate while true 1", expr: `
+			set x 0	
+			while (lt $x 5) {
+				echo $x
+				set x (add $x 1)
+			}
+			echo "done"`, want: "0\n1\n2\n3\n4\ndone\n(nil)\n"},
+		{desc: "iterate while true 2", expr: `
+			set x 20	
+			while (lt $x 5) {
+				echo $x
+				set x (add $x 1)
+			}
+			echo "done"`, want: "done\n(nil)\n"},
+		{desc: "iterate for ever with break 1", expr: `
+			set x 0
+			while {
+				echo $x
+				set x (add $x 1)
+				if (ge $x 5) {
+					break
+				}
+			}
+			echo "done"`, want: "0\n1\n2\n3\n4\ndone\n(nil)\n"},
+		{desc: "iterate for ever with break 2", expr: `
+			set x 0
+			echo (while {
+				echo $x
+				set x (add $x 1)
+				if (ge $x 5) {
+					break $x
+				}
+			})
+			`, want: "0\n1\n2\n3\n4\n5\n(nil)\n"},
+		{desc: "iterate for ever with continue", expr: `
+			set x 0
+			while {
+				set x (add $x 1)
+				if (or (eq $x 2) (eq $x 4)) {
+					echo "quack"
+					continue
+				}
+				echo $x	
+				if (ge $x 5) {
+					break
+				}
+			}
+			echo "done"`, want: "1\nquack\n3\nquack\n5\ndone\n(nil)\n"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+			err := evalAndDisplay(ctx, inst, tt.expr)
+
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, outW.String())
+		})
+	}
+}
+
 func TestBuiltins_Break(t *testing.T) {
 	tests := []struct {
 		desc string