From bb2354e8920f5e555fafe4d7162f44b11fa213d9 Mon Sep 17 00:00:00 2001
From: Sameer Rahmani <lxsameer@gnu.org>
Date: Wed, 1 Jan 2020 17:22:11 +0000
Subject: [PATCH] Let special form has been added

---
 .../java/serene/simple/LetSpecialForm.java    | 58 +++++++++++++++++++
 src/main/java/serene/simple/RootScope.java    |  1 -
 src/main/java/serene/simple/SpecialForm.java  |  3 +
 src/main/java/serene/simple/SymbolNode.java   | 50 ++++++++--------
 4 files changed, 86 insertions(+), 26 deletions(-)
 create mode 100644 src/main/java/serene/simple/LetSpecialForm.java

diff --git a/src/main/java/serene/simple/LetSpecialForm.java b/src/main/java/serene/simple/LetSpecialForm.java
new file mode 100644
index 0000000..56b4f7c
--- /dev/null
+++ b/src/main/java/serene/simple/LetSpecialForm.java
@@ -0,0 +1,58 @@
+/**
+ * Serene (simple) - A PoC lisp to collect data on Serenes concepts
+ * Copyright (C) 2019-2020 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA  02110-1301, USA.
+ */
+package serene.simple;
+
+public class LetSpecialForm extends SpecialForm {
+  private ListNode<Node> bindings;
+  private ListNode<Node> body;
+
+  public LetSpecialForm(ListNode<Node> listNode) {
+    super(listNode);
+
+    if (!(listNode.rest().first() instanceof ListNode)) {
+      throw new SereneException("Let bindings should be a list of pairs.");
+    }
+
+    this.bindings = (ListNode<Node>) listNode.rest().first();
+    this.body = listNode.rest().rest();
+  }
+
+  @Override
+  public Object eval(IScope scope) {
+    Scope letScope = new Scope(scope);
+
+    for (Object x : this.bindings) {
+      if (!(x instanceof ListNode))
+        throw new SereneException(String.format("Expect a pair instead of '%s'", x.toString()));
+
+      letScope.insertSymbol(
+        ((ListNode<Node>) x).first().toString(),
+        ((ListNode<Node>) x).rest().first().eval(letScope));
+    }
+
+    Object result = ListNode.EMPTY;
+
+    for(Node x: body) {
+      result = x.eval(letScope);
+    }
+
+    return result;
+  }
+}
diff --git a/src/main/java/serene/simple/RootScope.java b/src/main/java/serene/simple/RootScope.java
index d58cfd7..a930354 100644
--- a/src/main/java/serene/simple/RootScope.java
+++ b/src/main/java/serene/simple/RootScope.java
@@ -47,7 +47,6 @@ public class RootScope extends AScope {
       put("list", new ListFn());
       put("first", new FirstFn());
       put("rest", new RestFn());
-      //put("let", new LetFn());
       // put("cond", new CondFn());
       //put("reduce", new ReduceFn());
       put("System", System.class);
diff --git a/src/main/java/serene/simple/SpecialForm.java b/src/main/java/serene/simple/SpecialForm.java
index 75d2036..3bf3dcb 100644
--- a/src/main/java/serene/simple/SpecialForm.java
+++ b/src/main/java/serene/simple/SpecialForm.java
@@ -25,6 +25,7 @@ public class SpecialForm extends Node {
   private static final SymbolNode FN = new SymbolNode("fn");
   private static final SymbolNode IF = new SymbolNode("if");
   private static final SymbolNode QUOTE = new SymbolNode("quote");
+  private static final SymbolNode LET = new SymbolNode("let");
 
   public ListNode<Node> node;
 
@@ -39,6 +40,8 @@ public class SpecialForm extends Node {
       return l;
     } else if (l.first().equals(DEF)) {
       return new DefSpecialForm(l);
+    } else if (l.first().equals(LET)){
+      return new LetSpecialForm(l);
     } else if (l.first().equals(FN)) {
       return new FnSpecialForm(l);
     } else if (l.first().equals(IF)) {
diff --git a/src/main/java/serene/simple/SymbolNode.java b/src/main/java/serene/simple/SymbolNode.java
index 8854aeb..bce928f 100644
--- a/src/main/java/serene/simple/SymbolNode.java
+++ b/src/main/java/serene/simple/SymbolNode.java
@@ -20,33 +20,33 @@
 package serene.simple;
 
 public class SymbolNode extends Node {
-    public String name;
+  public String name;
 
-    public SymbolNode(String name) {
-        this.name = name;
+  public SymbolNode(String name) {
+    this.name = name;
+  }
+
+  @Override
+  public boolean equals(Node other) {
+    if (other instanceof SymbolNode) {
+      SymbolNode n = (SymbolNode) other;
+
+      if (this.name.equals(n.name)) {
+        return true;
+      }
+
+      return false;
     }
+    return super.equals(other);
+  }
 
-    @Override
-    public boolean equals(Node other) {
-        if (other instanceof SymbolNode) {
-            SymbolNode n = (SymbolNode) other;
+  @Override
+  public Object eval(IScope scope) {
+    return scope.lookupSymbol(this.name);
+  }
 
-            if (this.name.equals(n.name)) {
-                return true;
-            }
-
-            return false;
-        }
-        return super.equals(other);
-    }
-
-    @Override
-    public Object eval(IScope scope) {
-        return scope.lookupSymbol(this.name);
-    }
-
-    @Override
-    public String toString() {
-        return this.name;
-    }
+  @Override
+  public String toString() {
+    return this.name;
+  }
 }