document in all relevant places that delaying syntax error in check e…

…xpressions is intentional and provide an example of why this is so

htdp-doc/scribblings/htdp-langs/prim-ops.rkt

@@ -322,7 +322,7 @@
             [(check-expect expression expected-expression)]]{
 
    Checks that the first @racket[expression] evaluates to the same value as the
-   @racket[expected-expression].
+   @racket[expected-expression]. 
 
 @;%
 @(begin
@@ -341,8 +341,11 @@ A @racket[check-expect] expression must be placed at the top-level of a
  ahead of the tested function definition. By placing @racket[check-expect]s
  there, a programmer conveys to a future reader the intention behind the
  program with working examples, thus making it often superfluous to read
- the function definition proper. 
-
+ the function definition proper. Syntax errors in
+  @racket[check-expect] (and all check forms)
+are intentionally delayed to run time so that students can write tests
+@emph{without} necessarily writing complete function headers.  
+
 It is an error for @racket[expr] or @racket[expected-expr] to produce an
 inexact number or a function value. As for inexact numbers, it is
 @italic{morally} wrong to compare them for plain equality. Instead one

htdp-doc/test-engine/test-engine.scrbl

@@ -27,7 +27,9 @@ as parameters to configure the behavior of test reports.
 Each check form may only occur at the top-level; results are collected
 and reported by the test function.  Note that the check forms only
 register checks to be performed.  The checks are actually run by the
-@racket[test] function.
+@racket[test] function. Furthermore, syntax errors in check forms 
+are intentionally delayed to run time so that students can write tests
+@emph{without} necessarily writing complete function headers.  
 
 @defform[(check-expect expr expected-expr)]{
 Checks whether the value of the @racket[expr] expression is

htdp-lib/test-engine/README.md

@@ -10,7 +10,7 @@ teaching languages.
 - `test-engine.rkt`: register tests, run them, collect & inspect results
 - `racket-tests.rkt`: surface syntax for the teaching languages
 - `syntax.rkt`: utilities for defining surface syntax in a way that
-  works with the stepper
+     works with the stepper
 - `markup-gui.rkt`: graphical rendering for markup in a `text%` object
 - `test-markup.rkt`: convert test results into markup
 - `srcloc.rkt`: extract source location from the stack trace in an exception
@@ -32,3 +32,7 @@ the `simple-tree-text-markup` package.
 
 The teaching languages use `test-engine/markup-gui` to render in
 DrRacket.
+
+Note The test engine delays the reporting of error in `syntax.rkt` so
+that check expressions can be used without always writing a dummy
+function header. See note there. 

htdp-lib/test-engine/syntax.rkt

@@ -37,7 +37,20 @@
                          (syntax-column stx)
                          (syntax-position stx)
                          (syntax-span stx)))))
-  (define test-expr-checked-for-syntax-error #`(convert-compile-time-error #,test-expr))
+
+  ;; -----------------------------------------------------------------------------
+  ;; We want to delay compile-time errors in the check position of
+  #;   (check-expect check expect)
+  ;; to the run-time phase so that students are encourgaed to run
+  ;; partial programs and get feedback on some of the tests. The
+  ;; "exemplar" package (Shriram, Daniel Patterson, Ben Lerner and
+  ;; Northwestern?) relies on this property in that it requests that
+  ;; students formulate tests WITHOUT even formulating a function header. 
+
+  (define test-expr-checked-for-syntax-error
+  #`(convert-compile-time-error #,test-expr))
+  ;; -----------------------------------------------------------------------------
+
   (if (eq? 'module (syntax-local-context))
       #`(define #,bogus-name
           #,(stepper-syntax-property