From 4c0a1c3216548fbf3ec25af58fcadf7eced3dac3 Mon Sep 17 00:00:00 2001
From: bryan newbold <bnewbold@leaflabs.com>
Date: Tue, 18 Mar 2014 16:49:30 -0400
Subject: simple -> minimal

---
 minimal.scm | 250 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 250 insertions(+)
 create mode 100644 minimal.scm

(limited to 'minimal.scm')

diff --git a/minimal.scm b/minimal.scm
new file mode 100644
index 0000000..6e4c3c4
--- /dev/null
+++ b/minimal.scm
@@ -0,0 +1,250 @@
+
+; cyclic dependency graph (sigh)
+;
+; meaning
+;   expression-to-action
+;     list-to-action
+;       *application
+;         meaning
+;
+;   actions
+
+; ### preliminaries, utilities, shorthand
+
+; check if something is an atom vs {null, collection}
+(define atom?
+  (lambda (x)
+    (and (not (pair? x)) (not (null? x)))))
+
+; need a list or tuple type; tuples prefered
+(define first
+  (lambda (p) (car p)))
+
+(define second 
+  (lambda (p) (car (cdr p))))
+
+(define third
+  (lambda (p) (car (cdr (cdr p)))))
+
+(define build
+  (lambda (a b) (cons a (cons b (quote ())))))
+
+(define text-of second)
+
+; test functions
+(define add1 (lambda (x) (+ x 1)))
+(define sub1 (lambda (x) (- x 1)))
+
+; table operations
+(define new-entry build)
+
+(define lookup-in-entry
+  (lambda (name entry entry-f)
+    (lookup-in-entry-help name
+			  (first entry)
+			  (second entry)
+			  entry-f)))
+
+(define lookup-in-entry-help
+  (lambda (name names values entry-f)
+    (cond
+     ((null? names) (entry-f name))
+     ((eq? (car names) name) (car values))
+     (else (lookup-in-entry-help name (cdr names) (cdr values) entry-f)))))
+
+(define extend-table cons)
+
+(define lookup-in-table
+  (lambda (name table table-f)
+    (cond
+     ((null? table) (table-f name))
+     (else (lookup-in-entry name 
+			    (car table)
+			    (lambda (n)
+			      (lookup-in-table n (cdr table) table-f)))))))
+
+(define initial-table
+  (lambda (name)
+    (car (quote ()))))
+
+;(lookup-in-entry 'fish
+;		 '((teach a man to fish)
+;		   (1 2 3 4 5))
+;		 (lambda (x) x))
+
+;(lookup-in-table 'fish
+;		 (extend-table '((teach a man to fish)
+;				 (1 2 3 4 5))
+;			       (quote ()))
+;		 (lambda (x) x))
+
+; ### specific types/helpers
+(define builtin?
+  (lambda (l)
+    (eq? (first l) (quote builtin))))
+
+(define non-builtin?
+  (lambda (l)
+    (eq? (first l) (quote non-builtin))))
+
+(define else?
+  (lambda (x)
+    (cond
+     ((atom? x) (eq? x (quote else)))
+     (else #f))))
+
+(define table-of first)
+(define formals-of second)
+(define body-of third)
+(define question-of first)
+(define answer-of second)
+(define cond-lines-of cdr)
+(define function-of car)
+(define arguments-of cdr)
+
+; need generic true/false booleans, a number type, and a symbol type
+; also need a mutable "table" collection
+(define *const
+  (lambda (e table) 
+    (cond          
+     ((number? e) e) 
+     ((eq? e #t) #t)
+     ((eq? e #f) #f)
+     (else (build (quote builtin) e)))))
+;(*const 'asdf '()) ; (builtin asdf)
+
+(define *lambda
+  (lambda (e table)
+    (build (quote non-builtin) (cons table (cdr e)))))
+;(*lambda '(lambda (a b) (cond ((eq? a b) b) (else a))) '( ((1 2 3) (a b c))))
+;  (non-builtin ((((1 2 3) (a b c))) (a b) (cond ((eq? a b) b) (else a))))
+
+(define *quote
+  (lambda (e table)
+    (text-of e)))
+;(*quote '(quote stuff) '()) ; stuff
+
+(define *identifier
+  (lambda (e table)
+    (lookup-in-table e table initial-table)))
+;(*identifier 'asdf '()) ; error
+;(*identifier 'a '( ((1 2 3 a b c) (first second third 1 2 3)))) ; 1
+
+(define *cond
+  (lambda (e table)
+    (evcon (cond-lines-of e) table)))
+
+(define :atom?
+  (lambda (x)
+    (cond
+     ((atom? x) #t)
+     ((null? x) #f)
+     ((eq? (car x) (quote builtin)) #t)
+     ((eq? (car x) (quote non-builtin)) #t)
+     (else #f))))
+
+; ### now we start the meat!
+
+(define atom-to-action
+  (lambda (e)
+    (cond
+     ((number? e) *const)
+     ((eq? e #t) *const)
+     ((eq? e #f) *const)
+     ((eq? e (quote cons)) *const)
+     ((eq? e (quote car)) *const)
+     ((eq? e (quote cdr)) *const)
+     ((eq? e (quote null?)) *const)
+     ((eq? e (quote eq?)) *const)
+     ((eq? e (quote atom?)) *const)
+     ((eq? e (quote zero?)) *const)
+     ((eq? e (quote add1)) *const)
+     ((eq? e (quote sub1)) *const)
+     ((eq? e (quote number?)) *const)
+     (else *identifier))))
+;(atom-to-action 'number?); *const
+
+(define list-to-action
+  (lambda (e)
+    (cond
+     ((atom? (car e)) (cond
+		       ((eq? (car e) (quote quote)) *quote)
+		       ((eq? (car e) (quote lambda)) *lambda)
+		       ((eq? (car e) (quote cond)) *cond)
+		       (else *application)))
+     (else *application))))
+;(list-to-action '(lambda (x) x)) ; *lambda
+;(list-to-action '(cond ((eq? 1 2) #f) (else #t))) ; *cond
+
+(define expression-to-action
+  (lambda (e)
+    (cond
+     ((atom? e) (atom-to-action e))
+     (else (list-to-action e)))))
+;(expression-to-action '#f) ; *const
+;(expression-to-action '(lambda (x) x)) ; *lambda
+
+(define evcon
+  (lambda (lines table)
+    (cond
+     ((else? (question-of (car lines)))
+      (meaning (answer-of (car lines)) table))
+     ((meaning (question-of (car lines)) table)
+      (meaning (answer-of (car lines)) table))
+     (else (evcon (cdr lines) table)))))
+
+(define evlis
+  (lambda (args table)
+    (cond
+     ((null? args) (quote ()))
+     (else (cons (meaning (car args) table)
+		 (evlis (cdr args) table))))))
+;(evlis '(cons #f 4) '()) ; ((builtin cons) #f 4)
+
+(define *application
+  (lambda (e table)
+    (apply2
+     (meaning (function-of e) table)
+     (evlis (arguments-of e) table))))
+
+; basic, low-level, non-compound functions
+(define apply-builtin
+  (lambda (name vals)
+    (cond
+     ((eq? name (quote cons)) (cons (first vals) (second vals)))
+     ((eq? name (quote car)) (car (first vals)))
+     ((eq? name (quote cdr)) (cdr (first vals)))
+     ((eq? name (quote null?)) (null? (first vals)))
+     ((eq? name (quote eq?)) (eq? (first vals) (second vals)))
+     ((eq? name (quote atom?)) (:atom? (first vals)))
+     ((eq? name (quote zero?)) (zero? (first vals)))
+     ((eq? name (quote add1)) (add1 (first vals)))
+     ((eq? name (quote sub1)) (sub1 (first vals)))
+     ((eq? name (quote number?)) (number? (first vals))))))
+
+; for compound functions
+(define apply-closure
+  (lambda (closure vals)
+    (meaning (body-of closure)
+	     (extend-table (new-entry (formals-of closure) vals)
+			   (table-of closure)))))
+
+; this is "how apply would be implemented"; it isn't used in this file
+(define apply2
+  (lambda (fun vals)
+    (cond
+     ((builtin? fun) (apply-builtin (second fun) vals))
+     ((non-builtin? fun) (apply-closure (second fun) vals)))))
+
+; find the value of an s-expression in the context of an environment
+(define meaning
+  (lambda (e table)
+    ((expression-to-action e) e table)))
+;(meaning '(lambda (x) (cons x y)) '(((y z) ((8) 9))))
+; (non-primative ((((y z) ((8) 9)))) (x) (cons x y))
+
+; and finally, helper to find values in a starting environment
+(define value
+  (lambda (e)
+    (meaning e (quote ()))))
+;(value '((lambda (a b) (a (add1 b))) (lambda (c) (add1 c)) 4)) ; 6
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