snapshot: infix

Like parenthesize, I'm copying tests over from https://github.com/akkartik/wart
Unlike parenthesize, though, I can't just transliterate the code itself.
Wart was operating on an intermediate AST representation. Here I'm all
the way down to cells. That seemed like a good idea when I embarked, but
now I'm not so sure. Operating with the right AST data structure allowed
me to more easily iterate over the elements of a list. The natural recursion
for cells is not a good fit.

This patch and the next couple is an interesting case study in what makes
Unix so effective. Yes, you have to play computer, and yes it gets verbose
and ugly. But just diff and patch go surprisingly far in helping build a
picture of the state space in my brain.

Then again, there's a steep gradient of skills here. There are people who
can visualize state spaces using diff and patch far better than me, and
people who can't do it as well as me. Nature, nurture, having different
priorities, whatever the reason. Giving some people just the right crutch
excludes others.

1 files changed, 8 insertions, 2 deletions

diff --git a/shell/parse.mu b/shell/parse.mu
index c9e2901f..d888f56b 100644
--- a/shell/parse.mu
+++ b/shell/parse.mu
@@ -8,8 +8,8 @@ fn parse-input tokens: (addr stream token), out: (addr handle cell), trace: (add
     return
   }
   var close-paren?/eax: boolean <- copy 0/false
-  var dummy?/ecx: boolean <- copy 0/false
-  close-paren?, dummy? <- parse-sexpression tokens, out, trace
+  var dot?/ecx: boolean <- copy 0/false
+  close-paren?, dot? <- parse-sexpression tokens, out, trace
   {
     compare close-paren?, 0/false
     break-if-=
@@ -17,6 +17,12 @@ fn parse-input tokens: (addr stream token), out: (addr handle cell), trace: (add
     return
   }
   {
+    compare dot?, 0/false
+    break-if-=
+    error trace, "'.' is not a valid expression"
+    return
+  }
+  {
     var empty?/eax: boolean <- stream-empty? tokens
     compare empty?, 0/false
     break-if-!=