switch statement

Author: leafo

moonscript/parse.lua

@@ -272,7 +272,7 @@ local build_grammar = wrap_env(function()
 		CheckIndent = Cmt(Indent, check_indent), -- validates line is in correct indent
 		Line = (CheckIndent * Statement + Space * #Stop),
 
-		Statement = (Import + While + With + For + ForEach + Return
+		Statement = (Import + While + With + For + ForEach + Switch + Return
 			+ ClassDecl + Export + BreakLoop + Ct(ExpList) / flatten_or_mark"explist" * Space) * ((
 				-- statement decorators
 				key"if" * Exp * (key"else" * Exp)^-1 * Space / mark"if" +
@@ -298,6 +298,12 @@ local build_grammar = wrap_env(function()
 
 		With = key"with" * Exp * key"do"^-1 * Body / mark"with",
 
+		Switch = key"switch" * Exp * key"do"^-1 * Space^-1 * Break * SwitchBlock / mark"switch",
+
+		SwitchBlock = EmptyLine^0 * Advance * Ct(SwitchCase * (Break^1 * SwitchCase)^0 * (Break^1 * SwitchElse)^-1) * PopIndent,
+		SwitchCase = key"when" * Exp * key"then"^-1 * Body / mark"case",
+		SwitchElse = key"else" * Body / mark"else",
+
 		If = key"if" * Exp * key"then"^-1 * Body *
 			((Break * CheckIndent)^-1 * EmptyLine^0 * key"elseif" * Exp * key"then"^-1 * Body / mark"elseif")^0 *
 			((Break * CheckIndent)^-1 * EmptyLine^0 * key"else" * Body / mark"else")^-1 / mark"if",
@@ -317,7 +323,7 @@ local build_grammar = wrap_env(function()
 		CompFor = key"for" * Ct(NameList) * key"in" * (sym"*" * Exp / mark"unpack" + Exp) / mark"for",
 		CompClause = CompFor + key"when" * Exp / mark"when",
 
-		Assign = Ct(AssignableList) * sym"=" * (Ct(With + If) + Ct(TableBlock + ExpListLow)) / mark"assign",
+		Assign = Ct(AssignableList) * sym"=" * (Ct(With + If + Switch) + Ct(TableBlock + ExpListLow)) / mark"assign",
 		Update = Assignable * ((sym"..=" + sym"+=" + sym"-=" + sym"*=" + sym"/=" + sym"%=")/trim) * Exp / mark"update",
 
 		-- we can ignore precedence for now

moonscript/transform.lua

@@ -492,6 +492,54 @@ Statement = Transformer({
       })
     end
   end,
+  switch = function(self, node, ret)
+    local _, exp, conds = unpack(node)
+    print("compiling switch", ret)
+    local exp_name = NameProxy("exp")
+    local convert_cond
+    convert_cond = function(cond)
+      local t, case_exp, body = unpack(cond)
+      local out = { }
+      insert(out, t == "case" and "elseif" or "else")
+      if t ~= "else" then
+        if t ~= "else" then
+          insert(out, {
+            "exp",
+            case_exp,
+            "==",
+            exp_name
+          })
+        end
+      else
+        body = case_exp
+      end
+      if ret then
+        body = apply_to_last(body, ret)
+      end
+      insert(out, body)
+      return out
+    end
+    local first = true
+    local if_stm = {
+      "if"
+    }
+    local _list_0 = conds
+    for _index_0 = 1, #_list_0 do
+      local cond = _list_0[_index_0]
+      local if_cond = convert_cond(cond)
+      if first then
+        first = false
+        insert(if_stm, if_cond[2])
+        insert(if_stm, if_cond[3])
+      else
+        insert(if_stm, if_cond)
+      end
+    end
+    return build.group({
+      build.assign_one(exp_name, exp),
+      if_stm
+    })
+  end,
   class = function(self, node)
     local _, name, parent_val, tbl = unpack(node)
     local constructor = nil
@@ -856,6 +904,11 @@ Value = Transformer({
       node
     })
   end,
+  switch = function(self, node)
+    return build.block_exp({
+      node
+    })
+  end,
   chain = function(self, node)
     local stub = node[#node]
     if type(stub) == "table" and stub[1] == "colon_stub" then

moonscript/transform.moon

@@ -267,6 +267,45 @@ Statement = Transformer {
         }
       }
 
+  switch: (node, ret) =>
+    _, exp, conds = unpack node
+    print "compiling switch", ret
+
+    exp_name = NameProxy "exp"
+
+    -- convert switch conds into if statment conds
+    convert_cond = (cond) ->
+      t, case_exp, body = unpack cond
+      out = {}
+      insert out, t == "case" and "elseif" or "else"
+      if  t != "else"
+        insert out, {"exp", case_exp, "==", exp_name} if t != "else"
+      else
+        body = case_exp
+
+      if ret
+        body = apply_to_last body, ret
+
+      insert out, body
+
+      out
+
+    first = true
+    if_stm = {"if"}
+    for cond in *conds
+      if_cond = convert_cond cond
+      if first
+        first = false
+        insert if_stm, if_cond[2]
+        insert if_stm, if_cond[3]
+      else
+        insert if_stm, if_cond
+
+    build.group {
+      build.assign_one exp_name, exp
+      if_stm
+    }
+
   class: (node) =>
     _, name, parent_val, tbl = unpack node
 
@@ -473,6 +512,8 @@ Value = Transformer {
 
   if: (node) => build.block_exp { node }
   with: (node) => build.block_exp { node }
+  switch: (node) =>
+    build.block_exp { node }
 
   -- pull out colon chain
   chain: (node) =>

moonscript/types.lua

@@ -10,7 +10,8 @@ manual_return = data.Set({
 })
 cascading = data.Set({
   "if",
-  "with"
+  "with",
+  "switch"
 })
 ntype = function(node)
   if type(node) ~= "table" then

moonscript/types.moon

@@ -11,7 +11,7 @@ import insert from table
 manual_return = data.Set{"foreach", "for", "while", "return"}
 
 -- assigns and returns are bubbled into their bodies
-cascading = data.Set{ "if", "with" }
+cascading = data.Set{ "if", "with", "switch" }
 
 -- type of node as string
 ntype = (node) ->