Changeset 1066

Timestamp:

2015-06-10T09:12:53-07:00 (9 years ago)

Author:

Marek Rychlik

Message:

* empty log message *

File:

• branches/f4grobner/polynomial.lisp (modified) (1 diff)

branches/f4grobner/polynomial.lisp

@@ -322 +322 @@
   (declare (type poly p))
   (reduce (ring-gcd ring) (mapcar #'term-coeff (rest (poly-termlist p))) :initial-value (poly-lc p)))
+
+(defun parse-expr (&optional stream)
+  "Parser of infix expressions with integer/rational coefficients
+The parser will recognize two kinds of polynomial expressions:
+
+- polynomials in fully expanded forms with coefficients
+  written in front of symbolic expressions; constants can be optionally
+  enclosed in (); for example, the infix form
+        X^2-Y^2+(-4/3)*U^2*W^3-5
+  parses to
+        (+ (- (EXPT X 2) (EXPT Y 2)) (* (- (/ 4 3)) (EXPT U 2) (EXPT W 3)) (- 5))
+
+- lists of polynomials; for example
+        [X-Y, X^2+3*Z]          
+  parses to
+          (:[ (- X Y) (+ (EXPT X 2) (* 3 Z)))
+  where the first symbol [ marks a list of polynomials.
+
+-other infix expressions, for example
+        [(X-Y)*(X+Y)/Z,(X+1)^2]
+parses to:
+        (:[ (/ (* (- X Y) (+ X Y)) Z) (EXPT (+ X 1) 2))
+Currently this function is implemented using M. Kantrowitz's INFIX package."
+  (read-from-string
+   (concatenate 'string
+     "#I(" 
+     (with-output-to-string (s)
+       (loop
+         (multiple-value-bind (line eof)
+             (read-line stream t)
+           (format s "~A" line)
+           (when eof (return)))))
+     ")")))
+