1 files changed, 28 insertions, 1 deletions
diff --git a/tex/context/base/l-lpeg.lua b/tex/context/base/l-lpeg.lua
index fa3b210af..70c5f14e1 100644
--- a/tex/context/base/l-lpeg.lua
+++ b/tex/context/base/l-lpeg.lua
@@ -15,6 +15,23 @@ local lpeg = require("lpeg")
 
 local report = texio and texio.write_nl or print
 
+-- Watch this: Lua does some juggling with replacement values and although lpeg itself is agnostic of
+-- % characters, the replacement isn't. Now, in all of the context sources these are only a few cases
+-- where capture replacement instring happens. Interesting is that the string parsing already happens
+-- when the lpeg is made, but nevertheless is a not that useful (at least for me) feature that has the
+-- side effect that one always has to do %% in order to get a %. Okay, now that I know it is there, I
+-- might use it more often.
+--
+-- local p = P("@") / "%"
+-- lpeg.print(p) print(lpeg.match(p,"@"))
+--
+-- local p = P("@") / "%%"
+-- lpeg.print(p) print(lpeg.match(p,"@"))
+--
+-- local p = C("@") * C("!") / "%2%1"
+-- lpeg.print(p) print(lpeg.match(p,"@!"))
+
+
 -- local lpmatch = lpeg.match
 -- local lpprint = lpeg.print
 -- local lpp     = lpeg.P
@@ -50,7 +67,7 @@ local report = texio and texio.write_nl or print
 -- function lpeg.Carg (l) local p = lpcarg(l) report("LPEG Carg =") lpprint(l) return p end
 
 local type = type
-local byte, char, gmatch = string.byte, string.char, string.gmatch
+local byte, char, gmatch, format = string.byte, string.char, string.gmatch, string.format
 
 -- Beware, we predefine a bunch of patterns here and one reason for doing so
 -- is that we get consistent behaviour in some of the visualizers.
@@ -766,3 +783,13 @@ end
 --     utfchar(0x202F), -- narrownobreakspace
 --     utfchar(0x205F), -- math thinspace
 -- } )
+
+-- handy from within tex:
+
+local lpegmatch = lpeg.match
+
+local replacer = lpeg.replacer("@","%%") -- Watch the escaped % in lpeg!
+
+function string.tformat(fmt,...)
+    return format(lpegmatch(replacer,fmt),...)
+end