diff --git a/lang/interpret_test/TestAstFunc2/lambdafunc-recursive-double.txtar b/lang/interpret_test/TestAstFunc2/lambdafunc-recursive-double.txtar
index 770fe5179..9e42ca336 100644
--- a/lang/interpret_test/TestAstFunc2/lambdafunc-recursive-double.txtar
+++ b/lang/interpret_test/TestAstFunc2/lambdafunc-recursive-double.txtar
@@ -2,25 +2,25 @@
 import "fmt"
 
 # recursive function (not supported!)
-$sum1 = func($in) {
-	if $in < 0 {
-		-1 * $sum2(-1 * $in)
+$sum1 = func($i) {
+	if $i < 0 {
+		-1 * $sum2(-1 * $i)
 	} else {
-		if $in == 0 {
+		if $i == 0 {
 			0 # terminate recursion
 		} else {
-			$in + $sum2($in - 1)
+			$i + $sum2($i - 1)
 		}
 	}
 }
-$sum2 = func($in) {
-	if $in < 0 {
-		-1 * $sum1(-1 * $in)
+$sum2 = func($i) {
+	if $i < 0 {
+		-1 * $sum1(-1 * $i)
 	} else {
-		if $in == 0 {
+		if $i == 0 {
 			0 # terminate recursion
 		} else {
-			$in + $sum1($in - 1)
+			$i + $sum1($i - 1)
 		}
 	}
 }
diff --git a/lang/interpret_test/TestAstFunc2/lambdafunc-recursive.txtar b/lang/interpret_test/TestAstFunc2/lambdafunc-recursive.txtar
index d44fbbc76..d6e06c1ce 100644
--- a/lang/interpret_test/TestAstFunc2/lambdafunc-recursive.txtar
+++ b/lang/interpret_test/TestAstFunc2/lambdafunc-recursive.txtar
@@ -2,14 +2,14 @@
 import "fmt"
 
 # recursive function (not supported!)
-$sum = func($in) {
-	if $in < 0 {
-		-1 * $sum(-1 * $in)
+$sum = func($i) {
+	if $i < 0 {
+		-1 * $sum(-1 * $i)
 	} else {
-		if $in == 0 {
+		if $i == 0 {
 			0 # terminate recursion
 		} else {
-			$in + $sum($in - 1)
+			$i + $sum($i - 1)
 		}
 	}
 }
diff --git a/lang/interpret_test/TestAstFunc2/lexer-parser0.txtar b/lang/interpret_test/TestAstFunc2/lexer-parser0.txtar
index d12ca1bc7..eaf4aed5b 100644
--- a/lang/interpret_test/TestAstFunc2/lexer-parser0.txtar
+++ b/lang/interpret_test/TestAstFunc2/lexer-parser0.txtar
@@ -1,6 +1,7 @@
 -- main.mcl --
 import "fmt"
-
+# unfortunately, for now `in` is a reserved keyword, see:
+# https://github.com/purpleidea/mgmt/issues/728
 $map = 55
 $fn = func($in) { # in is a special keyword
 	13
@@ -12,5 +13,4 @@ func fn($in) { # in is a special keyword
 test fmt.printf("%d", $fn(0)) {}
 test fmt.printf("%d", fn(0)) {}
 -- OUTPUT --
-Vertex: test[13]
-Vertex: test[97]
+# err: errLexParse: parser: `syntax error: unexpected IN, expecting MAP_IDENTIFIER or IDENTIFIER` @5:2
diff --git a/lang/interpret_test/TestAstFunc2/lexer-parser1.txtar b/lang/interpret_test/TestAstFunc2/lexer-parser1.txtar
new file mode 100644
index 000000000..663b56ef7
--- /dev/null
+++ b/lang/interpret_test/TestAstFunc2/lexer-parser1.txtar
@@ -0,0 +1,10 @@
+-- main.mcl --
+$s = if 42 in [13, -5, 42, 0,] {	# make sure the `in` operator works
+	"pass"
+} else {
+	"fail"
+}
+
+test $s {}
+-- OUTPUT --
+Vertex: test[pass]
diff --git a/lang/interpret_test/TestAstFunc2/map-iterator0.txtar b/lang/interpret_test/TestAstFunc2/map-iterator0.txtar
index b443f5908..cd020351e 100644
--- a/lang/interpret_test/TestAstFunc2/map-iterator0.txtar
+++ b/lang/interpret_test/TestAstFunc2/map-iterator0.txtar
@@ -5,12 +5,12 @@ $fn = func($x) { # notable because concrete type is fn(t1) t2, where t1 != t2
 	len($x)
 }
 
-$in1 = ["a", "bb", "ccc", "dddd", "eeeee",]
+$ins = ["a", "bb", "ccc", "dddd", "eeeee",]
 
-$out1 = iter.map($in1, $fn)
+$out = iter.map($ins, $fn)
 
-$t1 = template("out1: {{ . }}", $out1)
+$t = template("out: {{ . }}", $out)
 
-test $t1 {}
+test $t {}
 -- OUTPUT --
-Vertex: test[out1: [1 2 3 4 5]]
+Vertex: test[out: [1 2 3 4 5]]
diff --git a/lang/interpret_test/TestAstFunc2/map-iterator2.txtar b/lang/interpret_test/TestAstFunc2/map-iterator2.txtar
index f9eb3b760..01dccb96e 100644
--- a/lang/interpret_test/TestAstFunc2/map-iterator2.txtar
+++ b/lang/interpret_test/TestAstFunc2/map-iterator2.txtar
@@ -5,9 +5,9 @@ $fn = func($x) { # ignore arg
 	42
 }
 
-$in = [5, 4, 3, 2, 1,]
+$ins = [5, 4, 3, 2, 1,]
 
-$out = iter.map($in, $fn)
+$out = iter.map($ins, $fn)
 
 $t = template("out: {{ . }}", $out)
 
diff --git a/lang/interpret_test/TestAstFunc2/map-iterator3.txtar b/lang/interpret_test/TestAstFunc2/map-iterator3.txtar
index 32435072f..dc9195b03 100644
--- a/lang/interpret_test/TestAstFunc2/map-iterator3.txtar
+++ b/lang/interpret_test/TestAstFunc2/map-iterator3.txtar
@@ -5,9 +5,9 @@ $fn = func($x) { # type changes from str to int
 	len($x)
 }
 
-$in = ["a", "bb", "ccc", "dddd", "eeeee",]
+$ins = ["a", "bb", "ccc", "dddd", "eeeee",]
 
-$out = iter.map($in, $fn)
+$out = iter.map($ins, $fn)
 
 $t = template("out: {{ . }}", $out)
 
diff --git a/lang/interpret_test/TestAstFunc2/map-iterator4.txtar b/lang/interpret_test/TestAstFunc2/map-iterator4.txtar
index b2bda417e..2d04a72e4 100644
--- a/lang/interpret_test/TestAstFunc2/map-iterator4.txtar
+++ b/lang/interpret_test/TestAstFunc2/map-iterator4.txtar
@@ -1,10 +1,10 @@
 -- main.mcl --
 import "iter"
 
-$in = ["a", "bb", "ccc", "dddd", "eeeee",]
+$ins = ["a", "bb", "ccc", "dddd", "eeeee",]
 
 # the inline lambda format is more readable with the func as the second arg
-$out = iter.map($in, func($x) {
+$out = iter.map($ins, func($x) {
 	len($x)
 
 })
diff --git a/lang/interpret_test/TestAstFunc2/stmtfunc-recursive-double.txtar b/lang/interpret_test/TestAstFunc2/stmtfunc-recursive-double.txtar
index 9b962ead3..6e5a7ac67 100644
--- a/lang/interpret_test/TestAstFunc2/stmtfunc-recursive-double.txtar
+++ b/lang/interpret_test/TestAstFunc2/stmtfunc-recursive-double.txtar
@@ -2,25 +2,25 @@
 import "fmt"
 
 # recursive function (not supported!)
-func sum1($in) {
-	if $in < 0 {
-		-1 * sum2(-1 * $in)
+func sum1($i) {
+	if $i < 0 {
+		-1 * sum2(-1 * $i)
 	} else {
-		if $in == 0 {
+		if $i == 0 {
 			0 # terminate recursion
 		} else {
-			$in + sum2($in - 1)
+			$i + sum2($i - 1)
 		}
 	}
 }
-func sum2($in) {
-	if $in < 0 {
-		-1 * sum1(-1 * $in)
+func sum2($i) {
+	if $i < 0 {
+		-1 * sum1(-1 * $i)
 	} else {
-		if $in == 0 {
+		if $i == 0 {
 			0 # terminate recursion
 		} else {
-			$in + sum1($in - 1)
+			$i + sum1($i - 1)
 		}
 	}
 }
diff --git a/lang/interpret_test/TestAstFunc2/stmtfunc-recursive.txtar b/lang/interpret_test/TestAstFunc2/stmtfunc-recursive.txtar
index 0ca7ed748..b43149cdc 100644
--- a/lang/interpret_test/TestAstFunc2/stmtfunc-recursive.txtar
+++ b/lang/interpret_test/TestAstFunc2/stmtfunc-recursive.txtar
@@ -2,14 +2,14 @@
 import "fmt"
 
 # recursive function (not supported!)
-func sum($in) {
-	if $in < 0 {
-		-1 * sum(-1 * $in)
+func sum($i) {
+	if $i < 0 {
+		-1 * sum(-1 * $i)
 	} else {
-		if $in == 0 {
+		if $i == 0 {
 			0 # terminate recursion
 		} else {
-			$in + sum($in - 1)
+			$i + sum($i - 1)
 		}
 	}
 }
diff --git a/lang/parser/lexer.nex b/lang/parser/lexer.nex
index bf603aa77..ca6e716f4 100644
--- a/lang/parser/lexer.nex
+++ b/lang/parser/lexer.nex
@@ -139,6 +139,11 @@
 			lval.str = yylex.Text()
 			return NOT
 		}
+/in/		{
+			yylex.pos(lval) // our pos
+			lval.str = yylex.Text()
+			return IN
+		}
 /\->/		{
 			yylex.pos(lval) // our pos
 			lval.str = yylex.Text()
@@ -306,11 +311,6 @@
 			lval.str = yylex.Text()
 			return IDENTIFIER
 		}
-/in/		{
-			yylex.pos(lval) // our pos
-			lval.str = yylex.Text()
-			return IN
-		}
 /[A-Z]([a-z0-9_]*[a-z0-9]+)?/
 		{
 			yylex.pos(lval) // our pos