tasks a-s

Task/Power-set/M4/power-set.m4

@@ -0,0 +1,22 @@
+define(`for',
+  `ifelse($#, 0, ``$0'',
+          eval($2 <= $3), 1,
+          `pushdef(`$1', `$2')$4`'popdef(
+             `$1')$0(`$1', incr($2), $3, `$4')')')dnl
+define(`nth',
+  `ifelse($1, 1, $2,
+          `nth(decr($1), shift(shift($@)))')')dnl
+define(`range',
+  `for(`x', eval($1 + 2), eval($2 + 2),
+       `nth(x, $@)`'ifelse(x, eval($2+2), `', `,')')')dnl
+define(`powerpart',
+  `{range(2, incr($1), $@)}`'ifelse(incr($1), $#, `',
+     `for(`x', eval($1+2), $#,
+        `,powerpart(incr($1), ifelse(
+           eval(2 <= ($1 + 1)), 1,
+           `range(2,incr($1), $@), ')`'nth(x, $@)`'ifelse(
+              eval((x + 1) <= $#),1,`,range(incr(x), $#, $@)'))')')')dnl
+define(`powerset',
+  `{powerpart(0, substr(`$1', 1, eval(len(`$1') - 2)))}')dnl
+dnl
+powerset(`{a,b,c}')