Check nasm availability and give good error message when not.

Author: dvanhorn

langs/a86/check-nasm.rkt

@@ -0,0 +1,39 @@
+#lang racket
+(provide check-nasm-available)
+(require racket/gui/dynamic)
+
+(define nasm-msg
+  #<<HERE
+nasm not found: either you have not installed nasm
+or it cannot be found in your PATH: ~a.~a
+HERE
+  )
+
+(define macosx-msg
+  #<<HERE
+
+
+It appears you launched DrRacket using Finder, which
+does properly set up the PATH environment variable.
+Try launching DrRacket from the command line using the
+'drracket' command.
+HERE
+  )
+
+(define (macos?)
+  (eq? 'macosx (system-type 'os)))
+
+;; This will lie if you happen to run drracket from /, but that's OK.
+(define (launched-with-finder?)
+  (equal? (string->path "/") (find-system-path 'orig-dir)))
+
+(define (drracket?)
+  (gui-available?))
+
+(define (check-nasm-available)
+  (unless (parameterize ([current-output-port (open-output-string)]
+                         [current-error-port (open-output-string)])
+            (system "nasm -v"))
+    (error (format nasm-msg
+                   (getenv "PATH")
+                   (if (and (drracket?) (macos?) (launched-with-finder?))  macosx-msg "")))))

langs/a86/interp.rkt

@@ -4,10 +4,13 @@
  [asm-interp    (-> (listof instruction?) any/c)]
  [asm-interp/io (-> (listof instruction?) string? any/c)])
 
-(require "printer.rkt" "ast.rkt" "callback.rkt"
+(require "printer.rkt" "ast.rkt" "callback.rkt" "check-nasm.rkt"
          (rename-in ffi/unsafe [-> _->]))
 (require (submod "printer.rkt" private))
 
+;; Check NASM availability when required to fail fast.
+(check-nasm-available)
+
 ;; Assembly code is linked with object files in this parameter
 (define current-objs
   (make-parameter '()))