From ff9db4f3a6ee2a2bb5c821b73d59ffe792cbbc27 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sun, 21 Jun 2015 20:02:40 -0700
Subject: * lisplib.c (ifa_set_entries): Add conda.

* share/txr/stdlib/ifa.tl (conda): New macro.

* tests/012/ifa.tl: Adding test for conda.

* txr.1: Documenting conda.
---
 ChangeLog               | 22 ++++++++++++++++++++++
 lisplib.c               |  2 +-
 share/txr/stdlib/ifa.tl |  7 +++++++
 tests/012/ifa.tl        | 25 +++++++++++++++----------
 txr.1                   | 34 ++++++++++++++++++++++++++++++++++
 5 files changed, 79 insertions(+), 11 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 4073fcb7..fa9d9d77 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,25 @@
+2015-06-21  Kaz Kylheku  <kaz@kylheku.com>
+
+	Version 109.
+
+	* RELNOTES: Updated.
+
+	* configure, txr.1: Bumped version and date.
+
+	* share/txr/stdlib/ver.tl: Likewise.
+
+	* tl.vim, txr.vim: Regenerated.
+
+2015-06-21  Kaz Kylheku  <kaz@kylheku.com>
+
+	* lisplib.c (ifa_set_entries): Add conda.
+
+	* share/txr/stdlib/ifa.tl (conda): New macro.
+
+	* tests/012/ifa.tl: Adding test for conda.
+
+	* txr.1: Documenting conda.
+
 2015-06-20  Kaz Kylheku  <kaz@kylheku.com>
 
 	* genman.txr: Rewrite the man2html-generated inner name links with hash
diff --git a/lisplib.c b/lisplib.c
index 33277b7b..8f530c29 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -98,7 +98,7 @@ static val ver_instantiate(val set_fun)
 
 static val ifa_set_entries(val dlt, val fun)
 {
-  val name[] = { lit("ifa"), nil };
+  val name[] = { lit("ifa"), lit("conda"), nil };
   set_dlt_entries(dlt, name, fun);
   return nil;
 }
diff --git a/share/txr/stdlib/ifa.tl b/share/txr/stdlib/ifa.tl
index 180e5231..bffe8246 100644
--- a/share/txr/stdlib/ifa.tl
+++ b/share/txr/stdlib/ifa.tl
@@ -50,3 +50,10 @@
                   (it-temp [temps pos-candidate]))
              ^(let* (,*(zip temps args) (it ,it-temp))
                 (if (,sym ,*temps) ,then ,else))))))))
+
+(defmacro conda (. pairs)
+  (tree-case pairs
+    (((test . forms) . rest) ^(ifa ,test (progn ,*forms)
+                                   (conda ,*rest)))
+    (() ())
+    (else (throwf 'eval-error "conda: bad syntax: ~s" pairs))))
diff --git a/tests/012/ifa.tl b/tests/012/ifa.tl
index d659399e..ae283abc 100644
--- a/tests/012/ifa.tl
+++ b/tests/012/ifa.tl
@@ -14,34 +14,39 @@
             (error "test case ~s failed to expand: expected is ~s" expr expected)))))
 
 ;; "it" is (+ 2 2)
-(ifa (> (+ 2 2) 0) (* it 2))
-
 (test (ifa (> (+ 2 2) 0) (* it 2))
-  8)
+      8)
 
 ;; "it" is (* x x)
 (test (let ((x 7))
-    (ifa (>= (* x x) 49)
-      (isqrt it)))
-  7)
+        (ifa (>= (* x x) 49)
+             (isqrt it)))
+      7)
 
 ;; ambiguous: is "it" x or is "it" y?
 (test (ifa (> x y) (print it)) :error)
 
 ;; "it" is (+ 3 (* 2 x))
 (test (let ((x 5))
-    (ifa (< 0 (+ 3 (* 2 x)) 20) (* 100 it)))
-  1300)
+        (ifa (< 0 (+ 3 (* 2 x)) 20) (* 100 it)))
+      1300)
 
 ;; "it" is (length '(a b c d))
 ;; Intuition: it" could also be '(a b c d)
 ;; TODO: deal specially with chains of unary functions.
 ;; How about it = (length ...), itt = '(a b c d)
 (test (ifa (not (oddp (length '(a b c d)))) it)
-  4)
+      4)
 
 ;; "it" is y because %x% is constantp
 (test (symacrolet ((%x% 42))
       (let ((y 41))
         (ifa (> %x% y) it)))
-    42)
+      42)
+
+(test (let ((x 5))
+        (conda
+          ((not (integerp x)) (list it))
+          ((oddp (+ 2 x)) (list it))))
+      (7))
+
diff --git a/txr.1 b/txr.1
index e3a61513..f043344d 100644
--- a/txr.1
+++ b/txr.1
@@ -10941,6 +10941,40 @@ form.
   -> (4)
 .cble
 
+.coNP Macro @ conda
+.synb
+.mets (conda >> {( test << form *)}*)
+.syne
+.desc
+The
+.code conda
+operator provides a multi-branching conditional evaluation of
+forms, similarly to the
+.code cond
+operator. Enclosed in the cond form are groups of forms expressed as lists.
+Each group must be a list of at least one form.
+
+The
+.code conda
+operator is anaphoric: it expands into a nested structure of zero or more
+.code ifa
+invocations, according to these patterns:
+
+.cble
+  (conda) -> nil
+  (conda (x y ...) ...) -> (ifa x (progn y ...) (conda z ...))
+.cblk
+
+Thus,
+.code conda
+inherits all the restrictions on the
+.meta test
+expressions from
+.codn ifa ,
+as well as the anaphoric
+.code it
+variable feature.
+
 .coNP Macro @ dotimes
 .synb
 .mets (dotimes >> ( var < count-form <> [ result-form ]) << body-form *)
-- 
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