From f1160da419dc820685d1d12f0ccaf9ff21af53c3 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Mon, 25 Jul 2011 15:12:04 -0400
Subject: [PATCH] add `for/sum', `for/product', etc.

---
 collects/racket/private/for.rkt          | 16 ++++++++++++
 collects/scribblings/reference/for.scrbl | 31 ++++++++++++++++++++++++
 collects/tests/racket/for-util.rkt       |  4 +++
 3 files changed, 51 insertions(+)

diff --git a/collects/racket/private/for.rkt b/collects/racket/private/for.rkt
index 3e855ef78f..530a84c220 100644
--- a/collects/racket/private/for.rkt
+++ b/collects/racket/private/for.rkt
@@ -21,6 +21,10 @@
              for/or for*/or
              for/first for*/first
              for/last for*/last
+             for/sum for*/sum 
+             (rename for/sum Σ) (rename for*/sum Σ*)
+             for/product for*/product 
+             (rename for/product ∏) (rename for*/product ∏*)
              for/hash for*/hash
              for/hasheq for*/hasheq
              for/hasheqv for*/hasheqv
@@ -1437,6 +1441,18 @@
     (lambda (rhs) rhs)
     (lambda (x) x))
 
+  (define-for-variants (for/sum for*/sum)
+    ([result 0])
+    (lambda (x) x)
+    (lambda (rhs) rhs)
+    (lambda (x) #`(+ result #,x)))
+
+  (define-for-variants (for/product for*/product)
+    ([result 1])
+    (lambda (x) x)
+    (lambda (rhs) rhs)
+    (lambda (x) #`(* result #,x)))
+
   (define-for-variants (for/hash for*/hash)
     ([table #hash()])
     (lambda (x) x)
diff --git a/collects/scribblings/reference/for.scrbl b/collects/scribblings/reference/for.scrbl
index 899e51d321..5f824c7425 100644
--- a/collects/scribblings/reference/for.scrbl
+++ b/collects/scribblings/reference/for.scrbl
@@ -161,6 +161,33 @@ result of the @racket[for/or] expression is
   (error "doesn't get here"))
 ]}
 
+@deftogether[(
+@defform[(for/sum (for-clause ...) body ...+)]
+@defform[(Σ (for-clause ...) body ...+)]
+)]{
+
+Iterates like @racket[for], but each result of the last @racket[body]
+is accumulated into a result with @racket[+].
+
+@examples[
+(for/sum ([i '(1 2 3 4)]) i)
+(Σ ([i (in-range 100)]) i)
+]}
+
+
+@deftogether[(
+@defform[(for/product (for-clause ...) body ...+)]
+@defform[(∏ (for-clause ...) body ...+)]
+)]{
+
+Iterates like @racket[for], but each result of the last @racket[body]
+is accumulated into a result with @racket[*].
+
+@examples[
+(for/product ([i '(1 2 3 4)]) i)
+(∏ ([i (in-range 1 5)]) i)
+]}
+
 
 @defform[(for/lists (id ...) (for-clause ...) body ...+)]{
 
@@ -240,6 +267,10 @@ nested.
 @defform[(for*/hasheqv (for-clause ...) body ...+)]
 @defform[(for*/and (for-clause ...) body ...+)]
 @defform[(for*/or (for-clause ...) body ...+)]
+@defform[(for*/sum (for-clause ...) body ...+)]
+@defform[(Σ* (for-clause ...) body ...+)]
+@defform[(for*/product (for-clause ...) body ...+)]
+@defform[(∏* (for-clause ...) body ...+)]
 @defform[(for*/first (for-clause ...) body ...+)]
 @defform[(for*/last (for-clause ...) body ...+)]
 @defform[(for*/fold ([accum-id init-expr] ...) (for-clause ...) body ...+)]
diff --git a/collects/tests/racket/for-util.rkt b/collects/tests/racket/for-util.rkt
index c7409b3fed..ca206b2097 100644
--- a/collects/tests/racket/for-util.rkt
+++ b/collects/tests/racket/for-util.rkt
@@ -64,6 +64,10 @@
        (test (list (for/last ([i gen]) i)) 'gen (for/and ([i gen]) (member i `seq)))
        (test `seq 'gen (for/or ([i gen]) (member i `seq)))
        (test (for/first ([i gen]) i) 'gen (for/or ([i gen]) (and (member i `seq) i)))
+       (test (for/sum ([i gen]) (if (number? i) i 0)) 'gen 
+             (for/fold ([n 0]) ([i gen]) (if (number? i) (+ i n) n)))
+       (test (for/product ([i gen]) (if (number? i) i 1)) 'gen 
+             (for/fold ([n 1]) ([i gen]) (if (number? i) (* i n) n)))
        (test #t 'gen (for/and ([(i k) (in-parallel gen `seq)])
                        (equal? i k)))
        (test #f 'gen (for/and ([i gen])