From 3bb695e2cf01b35fb5df46e2895bd11026f784a2 Mon Sep 17 00:00:00 2001
From: Sergiu Ivanov <sivanov@colimite.fr>
Date: Sat, 12 Dec 2020 23:35:40 +0100
Subject: [PATCH] utils: Move compose-related functions to their own section.

---
 scribblings/utils.scrbl | 52 ++++++++++++++++++++++++-----------------
 utils.rkt               | 31 +++++++++++++-----------
 2 files changed, 48 insertions(+), 35 deletions(-)

diff --git a/scribblings/utils.scrbl b/scribblings/utils.scrbl
index a713a96..b59123b 100644
--- a/scribblings/utils.scrbl
+++ b/scribblings/utils.scrbl
@@ -3,7 +3,7 @@
 	  (for-label racket/base graph "../utils.rkt"
 	  	     (only-in typed/racket/base
 		              Any AnyValues Listof String Sexp Number Pair
-			      List ->
+			      List -> compose
 			      cast)))
 
 @title[#:tag "utils"]{dds/utils: Various Utilities}
@@ -120,6 +120,35 @@ passed in the first argument.
 
 }
 
+@section{Composing typed functions}
+
+Typed Racket's @racket[compose] only takes two arguments, because in general it
+is difficult to specify that the return types and the argument types should be
+the same for two successive functions in the argument list.  This section
+defines some further utilities which make using @racket[compose]
+more comfortable.
+
+@defproc[(compose-n [proc (-> a a)] ...) (-> a a)]{
+
+Compose an arbitrary number of functions of type @racket[(-> a a)].
+
+@examples[#:eval utils-evaluator
+((compose-n add1 add1 add1) 3)
+]}
+
+@defproc*[([(compose-3 [proc1 (-> c d)] [proc2 (-> b c)] [proc3 (-> a b)]) (-> a d)]
+           [(compose-4 [proc1 (-> d e)] [proc2 (-> c d)] [proc3 (-> b c)] [proc4 (-> a b)]) (-> a e)])]{
+
+@racket[compose-i] composes @racket[i] functions.  The rightmost function is
+applied first.
+
+@examples[#:eval utils-evaluator
+(define (s->n [x : String]) (cast (string->number x) Number))
+(define fancy-add1 (compose-3 print add1 s->n))
+fancy-add1
+(fancy-add1 "1")
+]}
+
 @section{Org-mode interoperability}
 
 Org-mode supports laying out the output of code blocks as tables, which is very
@@ -199,27 +228,6 @@ element with @racket[string->any] or keeps it as is if it is not a string.
 (unstringify-pairs '(("a" . 1) ("b" . "(and a (not b))")))
 ]}
 
-@defproc[(compose-n [proc (-> a a)] ...) (-> a a)]{
-
-Compose an arbitrary number of functions of type @racket[(-> a a)].
-
-@examples[#:eval utils-evaluator
-((compose-n add1 add1 add1) 3)
-]}
-
-@defproc*[([(compose-3 [proc1 (-> c d)] [proc2 (-> b c)] [proc3 (-> a b)]) (-> a d)]
-           [(compose-4 [proc1 (-> d e)] [proc2 (-> c d)] [proc3 (-> b c)] [proc4 (-> a b)]) (-> a e)])]{
-
-@racket[compose-i] composes @racket[i] functions.  The rightmost function is
-applied first.
-
-@examples[#:eval utils-evaluator
-(define (s->n [x : String]) (cast (string->number x) Number))
-(define fancy-add1 (compose-3 print add1 s->n))
-fancy-add1
-(fancy-add1 "1")
-]}
-
 @defproc*[([(read-org-variable-mapping [str String]) (VariableMapping Any)]
            [(unorgv [str String]) (VariableMapping Any)])]{
 
diff --git a/utils.rkt b/utils.rkt
index 0222f4a..135fceb 100644
--- a/utils.rkt
+++ b/utils.rkt
@@ -129,6 +129,24 @@
                   '(x y z))))
 
 
+;;; =========================
+;;; Composing typed functions
+;;; =========================
+
+(: compose-n (All (a) (-> (-> a a) * (-> a a))))
+(define (compose-n . funcs)
+  (λ (x)
+    (for/foldr ([x x]) ([f funcs])
+      (f x))))
+
+(: compose-3 (All (a b c d) (-> (-> c d) (-> b c) (-> a b) (-> a d))))
+(define (compose-3 f1 f2 f3)
+  (λ (x) (f1 (f2 (f3 x)))))
+(: compose-4 (All (a b c d e) (-> (-> d e) (-> c d) (-> b c) (-> a b) (-> a e))))
+(define (compose-4 f1 f2 f3 f4)
+  (λ (x) (f1 (f2 (f3 (f4 x))))))
+
+
 ;;; =========================
 ;;; Org-mode interoperability
 ;;; =========================
@@ -226,19 +244,6 @@
     (check-equal? (unstringify-pairs '(("a" . 1) ("b" . "(and a (not b))")))
                   '((a . 1) (b . (and a (not b)))))))
 
-(: compose-n (All (a) (-> (-> a a) * (-> a a))))
-(define (compose-n . funcs)
-  (λ (x)
-    (for/foldr ([x x]) ([f funcs])
-      (f x))))
-
-(: compose-3 (All (a b c d) (-> (-> c d) (-> b c) (-> a b) (-> a d))))
-(define (compose-3 f1 f2 f3)
-  (λ (x) (f1 (f2 (f3 x)))))
-(: compose-4 (All (a b c d e) (-> (-> d e) (-> c d) (-> b c) (-> a b) (-> a e))))
-(define (compose-4 f1 f2 f3 f4)
-  (λ (x) (f1 (f2 (f3 (f4 x))))))
-
 (: read-org-variable-mapping (-> String (VariableMapping Any)))
 (define read-org-variable-mapping
   (compose-3