add slow factorial example

more blinken!

1 files changed, 28 insertions, 0 deletions

diff --git a/site/samples/slo-fac.fs b/site/samples/slo-fac.fs
new file mode 100644
index 0000000..0ba50ca
--- /dev/null
+++ b/site/samples/slo-fac.fs
@@ -0,0 +1,28 @@
+\ calculate factorial by creating a stack of all numbers between n and
+\ 1, then multiply every element of that stack together.
+\
+\ this uses only tail-position call/if, so the call stack never grows
+\ past the initial function call.
+\
+\ this is not meant to be efficient, just exercise parts of the system
+\ and be something nice to look at with blinken
+
+: count-to ( n -- n n-1 ... 1 )
+  dup
+  1 > if
+    dup 1 - count-to
+  then
+;
+
+: stack-mul ( n-x ... n x -- v )
+  dup
+  1 > if
+    rot rot * swap 1 - stack-mul
+  else
+    drop
+  then
+;
+
+5 count-to
+5 stack-mul
+drop