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Task/Amb/Tcl/amb-1.tcl

@@ -0,0 +1,24 @@
+set amb {
+    {the    that     a}
+    {frog   elephant thing}
+    {walked treaded  grows}
+    {slowly quickly}
+}
+
+proc joins {a b} {
+    expr {[string index $a end] eq [string index $b 0]}
+}
+
+foreach i [lindex $amb 0] {
+    foreach j [lindex $amb 1] {
+        if ![joins $i $j] continue
+        foreach k [lindex $amb 2] {
+            if ![joins $j $k] continue
+            foreach l [lindex $amb 3] {
+                if [joins $k $l] {
+                    puts [list $i $j $k $l]
+                }
+            }
+        }
+    }
+}

Task/Amb/Tcl/amb-2.tcl

@@ -0,0 +1,41 @@
+package require Tcl 8.6
+proc cp {args} {
+    coroutine cp.[incr ::cps] apply {{list args} {
+	yield [info coroutine]
+	foreach item $list {
+	    if {[llength $args]} {
+		set c [cp {*}$args]
+		while 1 { yield [list $item {*}[$c]] }
+	    } else { yield $item }
+	}
+	return -code break
+    }} {*}$args
+}
+proc amb {name filter args} {
+    coroutine $name apply {{filter args} {
+	set c [cp {*}$args]
+	yield [info coroutine]
+	while 1 {
+	    set value [$c]
+	    if {[{*}$filter $value]} { yield $value }
+	}
+	return -code break
+    }} $filter {*}$args
+}
+
+proc joins {a b} {
+    expr {[string index $a end] eq [string index $b 0]}
+}
+proc joins* list {
+    foreach a [lrange $list 0 end-1] b [lrange $list 1 end] {
+	if {![joins $a $b]} {return 0}
+    }
+    return 1
+}
+
+amb words joins* \
+    {the    that     a} \
+    {frog   elephant thing} \
+    {walked treaded  grows} \
+    {slowly quickly}
+while 1 { puts [words] }