Fix conditionals; rename eval->exec.

init.lua

@@ -3,7 +3,7 @@ local lume = require("lume")
 -- helper to turn Lua functions into Forth-like words take/return on stack
 local stack_fn = function(arg_count, f)
    return function(stack)
-      assert(#stack >= arg_count, "Stack underflow")
+      assert(#stack >= arg_count, "stack underflow")
       local args = lume.last(stack, arg_count)
       for _=1,arg_count do table.remove(stack) end
       lume.push(stack, f(unpack(args)))
@@ -22,18 +22,29 @@ local function read_till(env, stoppers)
    return token
 end
 
-
-
 local function compile_token(token, env, exec_token)
    if(not env.compiling) then return exec_token(env, token)
    elseif(env.compilers[token]) then env.compilers[token](env.stack, env, token)
    else table.insert(env.compiling, token) end
 end
 
-local function exec_body(body, env, exec_token)
+local function exec_word(body, env, exec_token)
    local i = 1
    while body[i] do
-      exec_token(env, body[i])
+      if(#env.conditionals == 0) then
+         exec_token(env, body[i])
+      elseif(body[i] == "then") then
+         assert(#env.conditionals > 0, "if/then mismatch")
+         table.remove(env.conditionals)
+      elseif(body[i] == "else") then
+         assert(#env.conditionals > 0, "if/else mismatch")
+         env.conditionals[#env.conditionals] =
+            not env.conditionals[#env.conditionals]
+      elseif(lume.last(env.conditionals)) then
+         exec_token(env, body[i])
+      elseif(body[i] == "if") then
+         while(body[i] and body[i] ~= "then") do i = i + 1 end
+      end
       i = i + 1
    end
 end
@@ -47,7 +58,7 @@ local function exec_token(env, token)
    elseif(type(env.dictionary[token]) == "function") then
       env.dictionary[token](env.stack, env)
    elseif(type(env.dictionary[token]) == "table") then
-      exec_body(env.dictionary[token], env, exec_token)
+      exec_word(env.dictionary[token], env, exec_token)
    else
       env.write("unknown word: " .. token .. "\n")
    end
@@ -60,8 +71,6 @@ local function exec(env, stoppers)
    return exec(env, stoppers)
 end
 
-
-
 local primitives = {
    swap = stack_fn(2, function(a, b) return b, a end),
    rot = stack_fn(3, function(a, b, c) return b, c, a end),
@@ -85,6 +94,10 @@ local primitives = {
       env.compiling = {}
       env.dictionary[pop_token(env)] = env.compiling
    end,
+   ["if"] = function(stack, env)
+      assert(#stack >= 1, "stack underflow")
+      table.insert(env.conditionals, table.remove(stack))
+   end,
    ["("] = function(_,  env) read_till(env, {")"}) end,
    [".s"] = function(stack, env)
       env.write(table.concat(lume.map(stack, tostring), " ") .. "\n")

test_core.lua

@@ -42,17 +42,15 @@ return {test_booleans=
            end,
         test_if=
            function()
-              -- assert_stack({1, 2}, "1 : f true if 2 then ; f")
-              -- assert_stack({1}, "1 : f false if 2 3 then ; f")
-              -- assert_stack({2, 8}, "true if 2 8 else 4 then")
-              -- assert_stack({4}, "false if 2 1 else 4 then")
-              -- assert_stack({92}, "true if 3 2 1 + = if 92 else 2 then then")
+              assert_stack({1, 2}, "1 : f true if 2 then ; f")
+              assert_stack({1}, "1 : f false if 2 3 then ; f")
+              assert_stack({2, 8}, ": f true if 2 8 else 4 then ; f")
+              assert_stack({4}, ": f false if 2 1 else 4 then ; f")
+              assert_stack({92},
+                 "true : f if 3 2 1 + = if 92 else 2 then then ; f")
+              assert_stack({32},
+                 ": f false if 77 2 1 + = if 92 else 2 then else 32 then ; f")
            end,
-        -- test_nested_if=
-        --    function()
-        --       assert_stack({32}, "false if 77 2 1 + = if 92 else 2 then "..
-        --          " else 32 then")
-        --    end,
         -- test_loops=
         --    function()
         --       assert_stack({55}, "0 1 10 do i + loop")