From fbed39423f61ed2a5262e8c07c897f66e4f1ce9e Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Thu, 6 Feb 2014 21:59:24 -0800
Subject: [PATCH] add bound/c to guarantee function is defined

---
 main-helper.rkt | 13 ++++++++++++-
 main.rkt        | 19 +++----------------
 2 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/main-helper.rkt b/main-helper.rkt
index 6b69122..d0f44e4 100644
--- a/main-helper.rkt
+++ b/main-helper.rkt
@@ -4,10 +4,21 @@
 (require (for-syntax racket/rerequire pollen/tools pollen/world))
 (require pollen/tools pollen/world)
 
-(provide (all-defined-out))
+(provide here-path get-here-path require-extras require-and-provide-extras bound/c
+         (rename-out (top~ #%top)))
 
 (module+ test (require rackunit))
 
+(define-syntax-rule (top~ . id)
+    (λ x `(id ,@x)))
+
+(define-syntax (bound/c stx)
+    (syntax-case stx ()
+      [(_ x)
+       (if (identifier-binding #'x )
+           #'x
+           #'(#%top . x))]))
+
 (define-for-syntax (put-file-in-require-form file)
   `(file ,(->string file)))
 
diff --git a/main.rkt b/main.rkt
index 56d74de..fc041cd 100644
--- a/main.rkt
+++ b/main.rkt
@@ -25,19 +25,6 @@
      (require pollen/tools pollen/main-helper)
      (require-and-provide-extras) ; brings in the project require files
      
-     ;; #%top binding catches ids that aren't defined
-     ;; here, convert them to basic xexpr
-     ;; #%top is a syntax transformer that returns a function
-     ;; λ x captures all the args (vs. λ(x), which only catches one)
-     ;; and id is not spliced because it's syntax, not a true variable
-     ;; WARNING! This is convenient for writing pollen documents
-     ;; (which is why it works this way)
-     ;; but it makes debugging tricky, because an undefined (symbol item ...)
-     ;; is just treated as a valid tagged-xexpr, not an undefined function.
-     (define-syntax-rule (#%top . id)
-       ;; todo: can #%top emit a debug message when a function hits it?
-       (λ x `(id ,@x)))
-     
      expr ... ; body of module  
      
      ;; set up a hook for identifier 'here'
@@ -47,9 +34,9 @@
      (provide (all-from-out ; pollen file should bring its requires
                pollen/tools))) 
    
-   (require 'pollen-inner) ; provides doc & #%top, among other things
+   (require 'pollen-inner) ; provides doc, among other things
    
-   (define here (path->pnode inner-here-path))
+   (define here ((bound/c path->pnode) inner-here-path))
    
    ;; prepare the elements, and append inner-here-path as meta.
    ;; put it first so it can be overridden by custom meta later on
@@ -85,7 +72,7 @@
    
    (define main (apply (if here-is-ptree?
                            ;; ptree source files will go this way,
-                           ptree-source-decode
+                           (bound/c ptree-source-decode)
                            ;; ... but other files, including pollen, will go this way.
                            ;; Root is treated as a function. 
                            ;; If it's not defined elsewhere,