From 602555a3178f8fa46ef68d162509717dc82ed1c0 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 9 Dec 2015 06:49:32 -0800
Subject: Bugfix: ifa must allow dwim expressions.

* share/txr/stdlib/ifa.tl (ifa): Accept dwim expressions
as the condition. Moreover, treat [f x] as a one-argument
call, even though it is the two-argument form (dwim f x).

* txr.1: Documented.
---
 share/txr/stdlib/ifa.tl |  9 ++++++---
 txr.1                   | 24 +++++++++++++++++++-----
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/share/txr/stdlib/ifa.tl b/share/txr/stdlib/ifa.tl
index aa406bbd..cefb38eb 100644
--- a/share/txr/stdlib/ifa.tl
+++ b/share/txr/stdlib/ifa.tl
@@ -35,11 +35,12 @@
                  (first test)))
        ^(ifa ,(second test) ,else ,then))
       (t (let* ((sym (first test))
-                (args (rest test))
+                (args (if (eq 'dwim sym) (cddr test) (cdr test)))
                 (n-candidate-args [count-if candidate-p args])
                 (pos-candidate (or [pos-if candidate-p args] 0)))
            (unless (or (lexical-fun-p e sym)
                        (and (or (functionp (symbol-function sym))
+                                (eq sym 'dwim)
                                 (null (symbol-function sym)))))
              (throwf 'eval-error "ifa: test expression must be \
                                  \ a simple function call"))
@@ -55,12 +56,14 @@
                  ^(let (,*(zip btemps before-it))
                     (placelet ((it ,it-form))
                       (let (,*(zip atemps after-it))
-                        (if (,sym ,*btemps it ,*atemps)
+                        (if (,sym ,*(if (eq 'dwim sym) ^(,(second test)))
+                                  ,*btemps it ,*atemps)
                           ,then ,else))))))
              (let* ((temps (mapcar (ret (gensym)) args))
                     (it-temp [temps pos-candidate]))
                ^(let* (,*(zip temps args) (it ,it-temp))
-                  (if (,sym ,*temps) ,then ,else)))))))))
+                  (if (,sym ,*(if (eq 'dwim sym) ^(,(second test)))
+                            ,*temps) ,then ,else)))))))))
 
 (defmacro conda (. pairs)
   (tree-case pairs
diff --git a/txr.1 b/txr.1
index dc863543..4d7a28a9 100644
--- a/txr.1
+++ b/txr.1
@@ -12271,12 +12271,24 @@ expression:
 .IP 1.
 The
 .meta cond
-expression must be either an atom, or a function call form:
-a compound expression with a symbol in the leftmost position
-which resolves to a function. Otherwise the
+expression must be either an atom, a function call form,
+or a
+.code dwim
+form.  Otherwise the
 .code ifa
 expression is ill-formed, and throws an exception at
-macro-expansion time.
+macro-expansion time. For the purposes of these rules,
+a
+.code dwim
+form is considered as a function call expression, whose first
+argument is the second element of the form. That is to say,
+.code [f x]
+which is equivalent to
+.code (dwim f x)
+is treated similarly to
+.code (f x)
+as a one-argument call.
+
 .IP 2.
 If the
 .meta cond
@@ -12301,7 +12313,9 @@ operator.
 .IP 4.
 If
 .meta cond
-is a function call with exactly one argument, then the
+is a function call or
+.code dwim
+expression with exactly one argument, then the
 .code it
 variable is bound to the argument expression, except when
 the function being called is
-- 
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