From 11cbf7647f7672243f39bd995d8c73c5a5a8424d Mon Sep 17 00:00:00 2001
From: Felix Martin <mail@felixm.de>
Date: Fri, 15 Jan 2021 14:38:24 -0500
Subject: [PATCH] Implement 4.1

---
 ex-4_01-xx.scm     |  23 +++++++-
 misc/evaluator.scm | 136 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 158 insertions(+), 1 deletion(-)
 create mode 100644 misc/evaluator.scm

diff --git a/ex-4_01-xx.scm b/ex-4_01-xx.scm
index 0667aba..efc9f86 100644
--- a/ex-4_01-xx.scm
+++ b/ex-4_01-xx.scm
@@ -1,4 +1,25 @@
 (load "util.scm")
+(load "misc/evaluator.scm")
 
-(display "\nex-4.1\n")
+(display "\nex-4.1 - list-of-values\n")
+
+(define (list-of-values-left-to-right exps env)
+  (if (no-operands? exps)
+      '()
+      (let ((first (eval (first-operand exps) env)))
+        (let ((rest ((list-of-values (rest-operands exps) env))))
+          (cons first rest)))))
+
+(define (list-of-values-right-to-left exps env)
+  (if (no-operands? exps)
+      '()
+      (let ((rest ((list-of-values (rest-operands exps) env))))
+        (let ((first (eval (first-operand exps) env)))
+          (cons first rest)))))
+
+(display "[done]\n")
+
+(display "\nex-4.2\n")
+
+(display "\nex-4.3\n")
 
diff --git a/misc/evaluator.scm b/misc/evaluator.scm
new file mode 100644
index 0000000..0feb4df
--- /dev/null
+++ b/misc/evaluator.scm
@@ -0,0 +1,136 @@
+(define (eval exp env)
+  (cond ((self-evaluating? exp) exp)
+        ((variable? exp) (lookup-variable-value exp env))
+        ((quoted? exp) (text-of-quotation exp))
+        ((assignment? exp) (eval-assignment exp env))
+        ((definition? exp) (eval-definition exp env))
+        ((if? exp) (eval-if exp env))
+        ((lambda? exp)
+         (make-procedure (lambda-parameters exp)
+                         (lambda-body exp)
+                         env))
+        ((begin? exp)
+         (eval-sequence (begin-actions exp) env))
+        ((cond? exp) (eval (cond->if exp) env))
+        ((application? exp)
+         (apply (eval (operator exp) env)
+                (list-of-values (operands exp) env)))
+        (else
+         (error "Unknown expression type -- EVAL" exp))))
+
+(define (apply procedure arguments)
+  (cond ((primitive-procedure? procedure)
+         (apply-primitive-procedure procedure arguments))
+        ((compound-procedure? procedure)
+         (eval-sequence
+           (procedure-body procedure)
+           (extend-environment
+             (procedure-parameters procedure)
+             arguments
+             (procedure-environment procedure))))
+        (else
+         (error
+          "Unknown procedure type -- APPLY" procedure))))
+
+(define (list-of-values exps env)
+  (if (no-operands? exps)
+      '()
+      (cons (eval (first-operand exps) env)
+            (list-of-values (rest-operands exps) env))))
+
+(define (eval-if exp env)
+  (if (true? (eval (if-predicate exp) env))
+      (eval (if-consequent exp) env)
+      (eval (if-alternative exp) env)))
+
+(define (eval-sequence exps env)
+  (cond ((last-exp? exps) (eval (first-exp exps) env))
+        (else (eval (first-exp exps) env)
+              (eval-sequence (rest-exps exps) env))))
+
+(define (eval-assignment exp env)
+  (set-variable-value! (assignment-variable exp)
+                       (eval (assignment-value exp) env)
+                       env)
+  'ok)
+
+(define (eval-definition exp env)
+  (define-variable! (definition-variable exp)
+                    (eval (definition-value exp) env)
+                    env)
+  'ok)
+
+(define (self-evaluating? exp)
+  (cond ((number? exp) true)
+        ((string? exp) true)
+        (else false)))
+
+(define (variable? exp) (symbol? exp))
+
+(define (quoted? exp)
+  (tagged-list? exp 'quote))
+
+(define (text-of-quotation exp) (cadr exp))
+
+(define (tagged-list? exp tag)
+  (if (pair? exp)
+      (eq? (car exp) tag)
+      false))
+
+(define (assignment? exp)
+  (tagged-list? exp 'set!))
+(define (assignment-variable exp) (cadr exp))
+(define (assignment-value exp) (caddr exp))
+
+(define (definition? exp)
+  (tagged-list? exp 'define))
+
+(define (definition-variable exp)
+  (if (symbol? (cadr exp))
+      (cadr exp)
+      (caadr exp)))
+
+(define (definition-value exp)
+  (if (symbol? (cadr exp))
+      (caddr exp)
+      (make-lambda (cdadr exp)   ; formal parameters
+                   (cddr exp)))) ; body
+
+(define (lambda? exp) (tagged-list? exp 'lambda))
+(define (lambda-parameters exp) (cadr exp))
+(define (lambda-body exp) (cddr exp))
+
+
+(define (make-lambda parameters body)
+  (cons 'lambda (cons parameters body)))
+
+(define (if? exp) (tagged-list? exp 'if))
+(define (if-predicate exp) (cadr exp))
+(define (if-consequent exp) (caddr exp))
+(define (if-alternative exp)
+  (if (not (null? (cdddr exp)))
+      (cadddr exp)
+      'false))
+
+(define (make-if predicate consequent alternative)
+  (list 'if predicate consequent alternative))
+
+(define (begin? exp) (tagged-list? exp 'begin))
+(define (begin-actions exp) (cdr exp))
+(define (last-exp? seq) (null? (cdr seq)))
+(define (first-exp seq) (car seq))
+(define (rest-exps seq) (cdr seq))
+
+(define (sequence->exp seq)
+  (cond ((null? seq) seq)
+        ((last-exp? seq) (first-exp seq))
+        (else (make-begin seq))))
+(define (make-begin seq) (cons 'begin seq))
+
+(define (application? exp) (pair? exp))
+(define (operator exp) (car exp))
+(define (operands exp) (cdr exp))
+(define (no-operands? ops) (null? ops))
+(define (first-operand ops) (car ops))
+(define (rest-operands ops) (cdr ops))
+