1 files changed, 157 insertions, 0 deletions
diff --git a/core/value.moon b/core/value.moon
new file mode 100644
index 0000000..f3f9796
--- /dev/null
+++ b/core/value.moon
@@ -0,0 +1,157 @@
+-- ALV Value types
+import Op, Action, FnDef from require 'core.base'
+
+local Scope
+load_ = ->
+  import Scope from require 'core.scope'
+
+ancestor = (klass) ->
+  assert klass, "cant find the ancestor of nil"
+  while klass.__parent
+    klass = klass.__parent
+  klass
+
+-- Result of evaluating an expression
+-- carries (all optional):
+-- - a Value
+-- - an Op (to update)
+-- - children (results of subexpressions that were evaluated)
+--
+-- ResultNodes form a tree that controls execution order and message passing
+-- between Ops.
+class ResultNode
+  -- params: table with optional keys op, value, children
+  new: (params={}) =>
+    @op = params.op
+    @value = params.value
+    @children = params.children or {}
+
+  -- unwrap value and assert that neither @op nor @children were set
+  value_only: (msg) =>
+    assert not @op and #@children == 0, msg or "pure expression expected"
+    @value
+
+  update: (dt) =>
+    for child in *@children
+      child\update dt
+    @op\update dt if @op
+
+  __tostring: =>
+    buf = "<result=#{@value}"
+    buf ..= " #{@op}" if @op
+    buf ..= " (#{#@children} children)" if #@children > 0
+    buf ..= ">"
+    buf
+
+local Const, Stream
+
+-- ALV Type wrapper
+class Value
+  -- @type      - type name.
+  --              builtin types: * literals: sym, num, bool
+  --                             * scope, opdef, fndef, builtin
+  -- @value     - Lua value - access through :unwrap()
+  new: (@type, @value) =>
+
+  -- asserts value-constness
+  -- returns self (for chaining)
+  const: => error 'not a constant'
+
+  -- unwrap to the Lua type
+  -- asserts @type == type, msg if given
+  unwrap: (type, msg) =>
+    assert type == @type, msg or "#{@} is not a #{type}" if type
+    @value
+
+-- static
+  __tostring: =>
+    value = if 'table' == (type @value) and rawget @value, '__base' then @value.__name else @value
+    "<#{@@__name} #{@type}: #{value}>"
+  __eq: (other) => other.type == @type and other.value == @value
+  __inherited: (cls) =>
+    cls.__base.__tostring = @__tostring
+    cls.__base.__eq = @__eq
+
+  -- wrap a Lua type
+  @wrap: (val, name='(unknown)') ->
+    typ = switch type val
+      when 'number' then 'num'
+      when 'string' then 'str'
+      when 'table'
+        if base = rawget val, '__base'
+          -- a class
+          switch ancestor val
+            when Op then 'opdef'
+            when Action then 'builtin'
+            else
+              error "#{name}: cannot wrap class '#{val.__name}'"
+        elseif val.__class
+          -- an instance
+          switch ancestor val.__class
+            when Scope then 'scope'
+            when FnDef then 'fndef'
+            when Value
+              return val
+            else
+              error "#{name}: cannot wrap '#{val.__class.__name}' instance"
+        else
+          -- plain table
+          return Const 'scope', Scope.from_table val
+      else
+        error "#{name}: cannot wrap Lua type '#{type val}'"
+
+    Const typ, val
+
+class Stream extends Value
+  new: (@type, @value=nil) =>
+
+  set: (@value) =>
+    -- set dirty flag (?)
+
+class Const extends Value
+  new: (type, value, @raw) =>
+    super type, value
+
+-- Value interface
+  const: => @
+
+-- AST interface
+  eval: (scope) =>
+    value = switch @type
+      when 'num', 'str'
+        @
+      when 'sym'
+        assert (scope\get @value), "undefined reference to symbol '#{@value}'"
+      else
+        error "cannot evaluate #{@}"
+
+    ResultNode :value
+
+  quote: => @
+
+  stringify: => @raw
+
+  clone: (prefix) => @
+  -- in case of doubt:
+  -- clone: (prefix) => Const @type, @value, @raw
+
+-- static
+  unescape = (str) -> str\gsub '\\([\'"\\])', '%1'
+
+  @parse: (type, sep) =>
+    switch type
+      when 'num' then (match) -> @ 'num', (tonumber match), match
+      when 'sym' then (match) -> @ 'sym', match, match
+      when 'str' then (match) -> @ 'str', (unescape match), sep .. match .. sep
+
+  @num: (num) -> Const 'num', num, tostring num
+  @str: (str) -> Const 'str', str, "'#{str}'"
+  @sym: (sym) -> Const 'sym', sym, sym
+  @bool: (bool) -> Const 'bool', bool, tostring bool
+
+{
+  :ResultNode
+  :Value
+  :Stream, :Const
+  :load_
+}