Extending Lua's string.gsub function with LPeg patterns

1 files changed, 52 insertions, 0 deletions

diff --git a/arabluatex.lua b/arabluatex.lua
index 8105311..e83206f 100644
--- a/arabluatex.lua
+++ b/arabluatex.lua
@@ -27,6 +27,58 @@ require("arabluatex_fullvoc")
 require("arabluatex_novoc")
 require("arabluatex_trans")
 
+-- arabluatex now uses lpeg
+local original_gsub = string.gsub
+function string.gsub(s, patt, repl)
+  if lpeg.type(patt) ~= "pattern" then
+    -- If patt isn't an LPEG pattern, revert to the normal gsub
+    return original_gsub(s, patt, repl)
+  else
+    -- Standardise repl to a function which takes the whole match
+    -- as the first argument, and then subsequent matches (if
+    -- there were any).
+    local typ = type(repl)
+    if typ == "table" then
+      local t = repl
+      repl = function(all, ...)
+        if select('#', ...) == 0 then
+          return t[all]
+        else
+          return t[...]
+        end
+      end
+    elseif typ == "string" then
+      local s = repl
+      repl = function(...)
+        local matches = {...}
+        return s:gsub("%%([0-9%%])", function(c)
+          if c == "%" then
+            return "%"
+          else
+            return matches[tonumber(c) + 1]
+          end
+        end)
+      end
+    elseif typ == "function" then
+      local f = repl
+      repl = function(all, ...)
+        if select('#', ...) == 0 then
+          return f(all)
+        else
+          return f(...)
+        end
+      end
+    else
+      error("Expected table / string / function")
+    end
+    return lpeg.Cs{
+      (lpeg.C(patt) / repl + 1) * lpeg.V(1) + true
+    }:match(s)
+  end
+end
+
+P = lpeg.P
+
 local function protectarb(str)
    str = string.gsub(str, "(\\arb.?)(%[.-%])(%b{})", "\\@arb%2%3")
    str = string.gsub(str, "(\\begin.?)(%b{})(%b[])", "\\@@begin{%2%3}")