process float/1 and pi/0

README.md

@@ -138,7 +138,7 @@ The following predicates are built-in to Scryer.
       `(rem)/2`, `(mod)/2`, `(/\)/2`, `(\/)/2`, `(>>)/2`,`(<<)/2`,
       `(\)/1`, `abs/1`, `sin/1`, `cos/1`, `tan/1`, `asin/1`, `acos/1`,
       `atan/1`, `atan2/2`, `log/1`, `exp/1`, `sqrt/1`, `float/1`,
-      `truncate/1`, `round/1`, `floor/1`, `ceiling/1`
+      `truncate/1`, `round/1`, `floor/1`, `ceiling/1`, `pi/0`
     * Comparison operators: `>`, `<`, `=<`, `>=`, `=:=`, `=\=`.
 * `(:)/2`
 * `(@>)/2`