From 91bdd22abc67a2575018399f6ebfba35ee9621c7 Mon Sep 17 00:00:00 2001
From: ben <benjaminlgreenman@gmail.com>
Date: Wed, 2 Mar 2016 14:21:51 -0500
Subject: [PATCH] [math] add espt

---
 math.rkt           | 18 ++++++++++++++++++
 math/no-colon.rkt  |  4 +++-
 test/math-fail.rkt |  2 ++
 test/math-pass.rkt | 14 ++++++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/math.rkt b/math.rkt
index 06040f4..98e10f1 100644
--- a/math.rkt
+++ b/math.rkt
@@ -7,6 +7,8 @@
   +: -: *: /:
   ;; Same signature as the racket/base operators,
   ;;  but try to simplify arguments during expansion.
+
+  expt:
 )
 
 (require (for-syntax
@@ -43,6 +45,22 @@
 (make-numeric-operator *)
 (make-numeric-operator /)
 
+(define-syntax (expt: stx)
+  (syntax-parse stx
+   [(_ e1 e2)
+    #:with e1+ (expand-expr #'e1)
+    #:with e2+ (expand-expr #'e2)
+    (let ([n1 (quoted-stx-value? #'e1+)]
+          [n2 (quoted-stx-value? #'e2+)])
+      (if (and (number? n1)
+               (number? n2))
+        (quasisyntax/loc stx #,(expt n1 n2))
+        (syntax/loc stx (expt e1+ e2+))))]
+   [_:id
+    (syntax/loc stx expt)]
+   [(_ e* ...)
+    (syntax/loc stx (expt e* ...))]))
+
 ;; -----------------------------------------------------------------------------
 
 (define-for-syntax (division-by-zero stx)
diff --git a/math/no-colon.rkt b/math/no-colon.rkt
index fba3512..911208b 100644
--- a/math/no-colon.rkt
+++ b/math/no-colon.rkt
@@ -6,4 +6,6 @@
   [+: +]
   [-: -]
   [*: *]
-  [/: /]))
+  [/: /]
+  [expt: expt]
+))
diff --git a/test/math-fail.rkt b/test/math-fail.rkt
index 824ea3c..0bd7575 100644
--- a/test/math-fail.rkt
+++ b/test/math-fail.rkt
@@ -12,11 +12,13 @@
   (ann (let ([n 2]) (-: 2 n)) Zero)
   (ann (let ([n 5]) (*: n 1/5 1)) One)
   (ann (let ([n 4]) (/: n n)) One)
+  (ann (let ([n 2]) (expt: 3 (-: n n))) One)
   ;; -- lambda => back to racket/base
   (ann ((lambda ([f : (-> Natural Natural Natural)]) (f 0 0)) +:) Zero)
   (ann ((lambda ([f : (-> Natural Natural Integer)]) (f 0 0)) -:) Zero)
   (ann ((lambda ([f : (-> Natural Natural Natural)]) (f 0 0)) *:) Zero)
   (ann ((lambda ([f : (-> Natural Natural Exact-Rational)]) (f 0 0)) /:) Zero)
+  (ann ((lambda ([f : (-> Natural Natural Natural)]) (f 0 1)) expt:) Zero)
   ;; -- dividing by zero => caught statically
   (/: 1 1 0)
   (/: 1 1 (+: 4 -2 -2))
diff --git a/test/math-pass.rkt b/test/math-pass.rkt
index c8ceb91..8fa1d91 100644
--- a/test/math-pass.rkt
+++ b/test/math-pass.rkt
@@ -79,4 +79,18 @@
   (check-equal? (ann (let ([n 5]) (*: 3 n (+: -1 2))) Natural) 15)
   (check-equal? (ann (let ([n 4]) (/: n n)) Positive-Exact-Rational) 1)
 
+  ;; -- expt
+  (check-equal?
+    (ann (expt: 5 3) Index)
+    125)
+  (check-equal?
+    (ann (expt: 99 0) One)
+    1)
+  (check-equal?
+    (ann (expt: (+: 5 -5) 78) Zero)
+    0)
+  (check-equal?
+    (ann (expt: (*: 2 2) (expt: 2 2)) Index)
+    256)
+
 )