rule out NaN in true props in types of positive? and negative? (#1227)

closes #750

Author: capfredf

typed-racket-lib/typed-racket/base-env/base-env-numeric.rkt

@@ -798,8 +798,8 @@
 [fixnum? (make-pred-ty -Fixnum)]
 [fixnum-for-every-system? (asym-pred Univ B (-PS (-is-type 0 -Fixnum) -tt))]
 [index? (make-pred-ty -Index)]
-[positive? (-> -Real B : (-PS (-is-type 0 -PosReal) (-is-type 0 -NonPosReal)))]
-[negative? (-> -Real B : (-PS (-is-type 0 -NegReal) (-is-type 0 -NonNegReal)))]
+[positive? (-> -Real B : (-PS (-is-type 0 -PosRealNoNan) (-is-type 0 -NonPosReal)))]
+[negative? (-> -Real B : (-PS (-is-type 0 -NegRealNoNan) (-is-type 0 -NonNegReal)))]
 [exact-positive-integer? (make-pred-ty -Pos)]
 [exact-nonnegative-integer? (make-pred-ty -Nat)]
 

typed-racket-test/unit-tests/typecheck-tests.rkt

@@ -541,6 +541,14 @@
               1.0
               x))
           -NonNegFlonum)
+        (tc-e/t (let ([a : (U One Float-Nan) 1])
+                  (if (positive? a) a
+                      1))
+                -One)
+        (tc-e/t (let ([a : (U Negative-Fixnum Float-Nan) -1])
+                  (if (negative? a) a
+                      -1))
+                -NegFixnum)
         (tc-e (exact->inexact (expt 10 (/ -120.0 20))) ; from rsound
               -NonNegInexactReal)
         (tc-e (flexpt 0.5 0.3) -NonNegFlonum)