[SUBDIRMK RFC v2 REPOST 4/4] README: v2: $-doubling and macro assistance

[Ian Jackson]

Provide a $-doubling regime which can be used for macros - and also
for complex recipe runes.

Use this to provide a way to write macros that seem like they will
work properly.  The rule-definition-macro-invocation syntax uses
${ } by analogy with block-structred languages.

Not implemented yet.  Also no S-o-b at this time!
---
 README | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/README b/README
index f726f9c..e9aef3a 100644
--- a/README
+++ b/README
@@ -321,6 +321,34 @@ So pathname syntax is a subset of:
 	`all' is extra special: every directory has an `all'
 	target, which corresponds to &TARGETS.
 
+
+DOLLAR DOUBLING AND MACRO ASSISTANCE
+------------------------------------
+
+$+		Starts dollar-doubling
+$-		Stops dollar-doubling
+	Both are idempotent and local to the file or context.  Where
+	we say "... is $-doubled" we mean $-doubling is locally
+	enabled, and restored afterwards.
+
+While dollar-doubling:
+
+$	=>	$$	including $'s produced by other
+			 &-expansions not mentioned here
+
+&\$	=>	$
+&$NN	=>	$(NN)	where N are digits
+&$(	=>	$(
+
+&:macro NAME	=> define NAME
+STUFF		   STUFF  [but $-doubled]
+&:endm		   endef
+
+&${...} =>	${eval ${call ...}}
+		(matches { } pairs to find the end)
+		... is $-doubled (unless it contains $- to turn that off)
+
+
 Subdirectory and variable naming
 --------------------------------
 
-- 
2.11.0