lang: make 0 and 0.0 falsey

README.md

@@ -133,9 +133,8 @@ but not between mixed types.
 There are boolean operators `and`, `or`, `not` behaving like in Python and Ruby:
 they are short-cirtuit and retain the type of an operand 
 (`1==1 and 42` will return 42). Non-boolean types can be a boolean operand;
-for this, there is a definition what is considered "falsey": `false`,
-empty string, and `nil`. This may at resemble Python, but note that the zero number
-is not considered falsey -- a behavior that may change in the future.
+for this, there is a definition what is considered "falsey": `false`, `nil`,
+empty string, and zero, like in Python.
 
 Boolean constants are `true` and `false`.
 Another constant is `nil`, whose meaning is that

test.py

@@ -39,10 +39,14 @@
     [13.2, 'print not 1>3.0',   'true'],
     [13.3, 'print not 1.0>3.0', 'true'],
     [13.4, 'print not 3<=1',    'true'],
-    [14,   'print 1<2 and 0 or "whatever"',     '0'],
-    [14.1, 'print 1.0<2 and 0 or "whatever"',   '0'],
-    [14.2, 'print 1<2.0 and 0 or "whatever"',   '0'],
-    [14.3, 'print 1.0<2.0 and 0 or "whatever"', '0'],
+    [14,   'print 1<2 and 0 or "whatever"',       'whatever'],
+    [14.1, 'print 1.0<2 and 0 or "whatever"',     'whatever'],
+    [14.2, 'print 1<2.0 and 0 or "whatever"',     'whatever'],
+    [14.3, 'print 1.0<2.0 and 0 or "whatever"',   'whatever'],
+    [14.4, 'print 1<2 and 0.0 or "whatever"',     'whatever'],
+    [14.5, 'print 1.0<2 and 0.0 or "whatever"',   'whatever'],
+    [14.6, 'print 1<2.0 and 0.0 or "whatever"',   'whatever'],
+    [14.7, 'print 1.0<2.0 and 0.0 or "whatever"', 'whatever'],
     [15,   'print 1>2 or true and 42', '42'],
     [16,   'print 1<10/5 and 127*-1+154', '27'],
     [17, 'print "q"*2', 'qq'],
@@ -320,8 +324,8 @@
     [105.4, 'print nil>"ab"', '',  "err: GT: invalid types: nil, string "],
     [105.5, 'print nil>nil', '',   "err: GT: invalid types: nil, nil"],
 
-    [106.1,  'print not 0',        'false'],
-    [106.2,  'print not 0.0',      'false'],
+    [106.1,  'print not 0',        'true'],
+    [106.2,  'print not 0.0',      'true'],
     [106.3,  'print not false',    'true'],
     [106.4,  'print not ""',       'true'],
     [106.5,  'print not nil',      'true'],

value.go

@@ -32,6 +32,10 @@ func isFalsey(v value) bool {
 	switch x := v.(type) {
 	case bool:
 		return !x
+	case int:
+		return x == 0
+	case float64:
+		return x == 0.0
 	case string:
 		return x == ""
 	default: