1 files changed, 66 insertions, 0 deletions
diff --git a/ast.moon b/ast.moon
new file mode 100644
index 0000000..39e2f21
--- /dev/null
+++ b/ast.moon
@@ -0,0 +1,66 @@
+class Atom
+  new: (@raw, @style='', @value) =>
+
+  _walk_sexpr: =>
+
+  stringify: =>
+    switch @style
+      when ''
+        @raw
+      when '"'
+        "\"#{@raw}\""
+      else
+        error!
+
+  @make_num: (match) -> Atom match, '', tonumber match
+  @make_sym: (match) -> Atom match, '', match
+  @make_str: (match) -> Atom match, '"', match
+
+class Xpr
+  new: (parts, @style='(', tag) =>
+    @white = {}
+    @white[0] = parts[1]
+
+    for i = 2,#parts,2
+      @[i/2] = parts[i]
+      @white[i/2] = parts[i+1]
+
+    if tag
+      @tag = tag.value
+
+  _walk_sexpr: =>
+    if @style == '('
+      coroutine.yield @
+
+    for frag in *@
+      frag\_walk_sexpr!
+
+  walk_sexpr: =>
+    coroutine.wrap -> @_walk_sexpr!
+
+  stringify: =>
+    buf = ''
+    buf ..= @white[0]
+    for i, frag in ipairs @
+      buf ..= frag\stringify!
+      buf ..= @white[i]
+
+    switch @style
+      when 'naked'
+        buf
+      else
+        tag = if @tag then "[#{@tag}]" else ''
+        '(' .. tag .. buf .. ')'
+
+  make_sexpr: (tag, parts) ->
+    if parts
+      Xpr parts, '(', tag
+    else
+      Xpr tag, '('
+
+  make_nexpr: (parts) -> Xpr parts, 'naked'
+
+{
+  :Atom
+  :Xpr
+}