: fail ( -- )\r
failure get [ continue ] [ amb-failure ] if* ;\r
\r
-: require ( ? -- )\r
+: must-be-true ( ? -- )\r
[ fail ] unless ;\r
\r
MACRO: checkpoint ( quot -- quot' )\r
: if-amb ( true false -- ? )\r
[\r
[ { t f } amb ]\r
- [ '[ @ require t ] ]\r
+ [ '[ @ must-be-true t ] ]\r
[ '[ @ f ] ]\r
tri* if\r
] amb-preserve ; inline\r