Refactor the main parser to use the bind macro.

The metabang-bind lib offers a nice bind macro that solves the problem
of ignoring bindings in destructuring-bind, and allows a let* approach
to nested destructuring (wven when mixed with let declarations).

Using that lib (that we already indirectly depend on anyway) simplifies
the parser code substantially.

pgloader.asd

@@ -30,6 +30,7 @@
                  #:cl-base64            ; Decode base64 data
 		 #:trivial-backtrace  	; For --debug cli usage
                  #:cl-markdown          ; To produce the website
+                 #:metabang-bind        ; the bind macro
 		 )
     :components
     ((:module "src"
@@ -38,6 +39,10 @@
 	       (:file "package" :depends-on ("params"))
                (:file "queue"   :depends-on ("params" "package"))
 
+               (:module "monkey"
+                        :components
+                        ((:file "bind")))
+
                (:module "utils"
                         :depends-on ("package" "params")
                         :components
@@ -67,7 +72,7 @@
                                              "schema"))))
 
                (:module "parsers"
-                        :depends-on ("params" "package" "utils" "pgsql")
+                        :depends-on ("params" "package" "utils" "pgsql" "monkey")
                         :components
                         ((:file "parse-ini")
                          (:file "parser")

src/monkey/bind.lisp

@@ -0,0 +1,10 @@
+;;;
+;;; Monkey patch metaband-bind macro to ignore nil:
+;;;
+;;;  https://github.com/gwkkwg/metabang-bind/issues/9
+;;;
+
+(in-package #:metabang.bind)
+
+(defun var-ignorable-p (var)
+  (and (symbolp var) (string= (symbol-name var) (symbol-name '_))))

src/package.lisp

@@ -158,7 +158,8 @@
   (:export #:read-queries))
 
 (defpackage #:pgloader.parser
-  (:use #:cl #:esrap #:pgloader.params #:pgloader.utils #:pgloader.sql)
+  (:use #:cl #:esrap #:metabang.bind
+        #:pgloader.params #:pgloader.utils #:pgloader.sql)
   (:import-from #:alexandria #:read-file-into-string)
   (:import-from #:pgloader.pgsql
 		#:with-pgsql-transaction