Error handling: Replace or update many calls to `die'

[subdirmk.git] / README

diff --git a/README b/README
index 7de4def345f95bdfa39f6da34992be894b22e11f..20658ae2adc3087e1f24db87cababc19aaa154b9 100644 (file)
--- a/README
+++ b/README
@@ -254,7 +254,7 @@ So pathname syntax is a subset of:
 &&             =>      &&              for convenience in shell runes
 
 &\&            =>      &               general escaping mechanism
-&\$            =>      $
+&\$            =>      $               provided for $-doubling regimes
 &\NEWLINE                              eats the newline and vanishes
 
 &$VARIABLE     =>      $(sub_dir_VARIABLE)     or $(TOP_VARIABLE)
@@ -323,6 +323,47 @@ 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.
+
+Sometimes we will show $'s being doubled inside another construct.
+This means the content of the construct is $-doubled: $-doubling is
+locally enabled, and restored afterwards.
+
+&:macro NAME   =>      define NAME
+STUFF $ THINGS ..      STUFF $$ THINGS
+&:endm         ..      endef
+       NAME is processed for &
+
+&${..$..} =>   ${eval ${call ..$$..}}
+       (matches { } pairs to find the end)
+       content is $-doubled (unless it contains $- to turn that off)
+
+       Together &:macro and &${...} provide a more reasonable macro
+       facility than raw make.  They solve the problem that make
+       expansions cannot directly generate multiple rules, variable,
+       etc.; instead, `$(eval )' must be used, but that re-expands
+       the argument, meaning that all the literal text must be
+       $-doubled.  This applies to the macro text and to the
+       arguments.  Also `$(eval $(call ...))' is an unfortunate syntax.
+       Hence &:macro and &${...}.
+
+While dollar-doubling:
+- - - - - - - - - - -
+
+$      =>      $$      including $'s produced by other
+                        &-expansions not mentioned here
+
+&\$    =>      $
+&$NN   =>      $(NN)   where N are digits
+&$(    =>      $(
+
+
 Subdirectory and variable naming
 --------------------------------