From 773f195f371d1c2eea3cb029fbbcca3f36d584b3 Mon Sep 17 00:00:00 2001
From: Pekka Laiho <pekka.i.laiho@gmail.com>
Date: Thu, 28 May 2020 19:41:41 +0700
Subject: [PATCH] eval according to example

---
 src/Evaller.php | 91 +++++++++++++++++++------------------------------
 1 file changed, 35 insertions(+), 56 deletions(-)

diff --git a/src/Evaller.php b/src/Evaller.php
index 8c51ea2..6851dbd 100644
--- a/src/Evaller.php
+++ b/src/Evaller.php
@@ -16,64 +16,43 @@ class Evaller
         return $results;
     }
 
-    public function doEval($expr, Env $env)
+    public function evalAst($ast, Env $env)
     {
-        if ($expr instanceof MList && $expr->count() > 0) {
-            $first = $expr->get(0);
-
-            if ($first instanceof Symbol) {
-                // Special built-in features
-                if ($first->getName() == 'env') {
-                    return $env;
-                } elseif ($first->getName() == 'quote') {
-                    if ($expr->count() != 2) {
-                        throw new MadLispException("quote requires exactly 1 argument");
-                    }
-
-                    return $expr->get(1);
-                } elseif ($first->getName() == 'if') {
-                    if ($expr->count() != 4) {
-                        throw new MadLispException("if requires exactly 3 arguments");
-                    }
-
-                    // Eval condition
-                    $result = $this->doEval($expr->get(1), $env);
-
-                    // Eval true or false branch and return it
-                    if ($result == true) {
-                        return $this->doEval($expr->get(2), $env);
-                    } else {
-                        return $this->doEval($expr->get(3), $env);
-                    }
-                }
-
-                // Normal symbol, fetch from env
-                $first = $env->get($first->getName());
-            }
-
-            if (!($first instanceof Closure)) {
-                throw new MadLispException("first argument of list is not function");
-            }
-
-            $args = array_slice($expr->getData(), 1);
-
-            // Evaluate args
-            $args = array_map(fn ($a) => $this->doEval($a, $env), $args);
-
-            // Call func and return result
-            return $first(...$args);
-        } elseif ($expr instanceof Hash) {
-            // Hash: return new hash with all items evaluated
-            $items = [];
-            foreach ($expr->getData() as $key => $val) {
-                $items[$key] = $this->doEval($val, $env);
-            }
-            return new Hash($items);
-        } elseif ($expr instanceof Symbol) {
-            return $env->get($expr->getName());
+        if ($ast instanceof Symbol) {
+            // Lookup symbol from env
+            return $env->get($ast->getName());
+        } elseif ($ast instanceof MList) {
+            // Eval contents and return new list
+            $results = array_map(fn ($a) => $this->doEval($a, $env), $ast->getData());
+            return new MList($results);
         }
 
-        // Return the expression unchanged
-        return $expr;
+        return $ast;
+    }
+
+    public function doEval($ast, Env $env)
+    {
+        // Not list
+        if (!($ast instanceof MList)) {
+            return $this->evalAst($ast, $env);
+        }
+
+        // Empty list
+        if ($ast->count() == 0) {
+            return $ast;
+        }
+
+        // Get new evaluated list
+        $ast = $this->evalAst($ast, $env);
+
+        $first = $ast->get(0);
+
+        if (!($first instanceof Closure)) {
+            throw new MadLispException("first item of list is not function");
+        }
+
+        $args = array_slice($ast->getData(), 1);
+
+        return $first(...$args);
     }
 }