Things With 'Infix' In The Title:

- ugly-tiny-infix-macro - This is a powerful lisp macro for the purpose of writing your expressions in infix notation while not losing out on lisp's power

## Infix reader-macro by Mark Kantrowitz.

Available from:

The Changelog from the cclan version reads

2005-06-06: * infix.cl: bind *read-suppress* in infix-reader to support the use of infix notation when *read-suppress* is true. Christophe Rhodes <csr21@cam.ac.uk> 2002-03-04: * infix.cl: moved definition of infix-error macro to before its first use. Christophe Rhodes <csr21@cam.ac.uk>.

This is not the most volatile piece of software.

Incidentally, it's probably non-free — there's a non-commercial clause in the licence.

There is also a Debian package.

Another package by Alan Manuel Gloria can be found here, but it's buggy on expressions like

(nfx 55 - 3 * 4 + 2000000)

(giving -1999957 instead of the correct result 2000043. There seems to be a problem with different operators of the same precedence.

Here's a corrected version of the macro implementation:

;; infix.lisp ;; by AmkG ;; Title : Infix notation macro ;; Filename : infix.lisp ;; Written by : Alan Manuel K. Gloria <almkglor@gmail.com> ;; Corrected by : Bruno Daniel <bruno.daniel@gmx.net> ;; Copyright status: ;; Err. I don't care? Okay, I do care. To be honest, I'll just ;; be plain happy if somebody ELSE uses this. Drop me a line, ;; or something. Or don't. I built this for my own amusement, ;; so if anyone else is amused too, well, drop me a line! ;; tested on: ;; clisp ;; gcl ;; sbcl ;; ecl ;; infix notation: ;; Lisp has traditionally used prefix notation for all formulae: in this ;; notation, the operation to be performed is specified before the ;; operands it is to be performed on. This simple notation gives a ;; consistent, regular syntax which greatly facilitates ;; metaprogramming. ;; However, one weakness of prefix notation is that some simple ;; algebraic/arithmetic operations do not and cannot follow the ;; traditional syntax taught to us during elementary - that is, the ;; notation we are used to in arithmetic is not prefix, but infix ;; notation: ;; 1 + 2 - 4 * 5 ;; In Lisp this would be: ;; (- (+ 1 2) (* 4 5))) ;; Despite the inherent advantages of prefix notation, sometimes ;; it's just much easier to write mathematical formulae a little more ;; like the way we actually write them on paper. ;; This file contains a macro, 'nfx, which allows for such an infix ;; notation. There are limitations: you need to put a LOT of spaces ;; in the formula: ;; (nfx 1+2-3) ;would confuse the Lisp parser ;; (nfx 1 + 2 - 3) ;would be understood ;; You can't use certain symbols as variable names: ;; (setf + 42) ;; (nfx (max + 3)) ; would look awfully like +(max,3), not max(+,3) ;; ...but you can embed prefix notation in it! ;; (nfx 1 + (- x 100)) ;it's valid! ;; (nfx 1 + (- x (3 * 3))) ;it's ALSO valid! ;; (nfx 1 + (- x 3 * 3)) ;err... this can give you unexpected behavior ;; ...also, you can define your own infix symbols using definfix: ;; (definfix my-infix-symbol ;; :precedence 40 ;; :function-name +) ;; (nfx 1 my-infix-symbol 2) ;; => 3 ;; send any feedback, bugreports, bugfixes, and cute girls to: ;; almkglor@gmail.com ;; This file defines a macro of the form (nfx ...) whose ;; parameters are a stream of LISP "tokens" (either symbols, ;; constants, or lists). The stream of tokens is interpreted ;; in infix notation. The macro then expands to the prefix ;; form equivalent to the infix form ;; Ex. ;; (macroexpand-1 '(nfx foo = 32)) ;; => (setf foo 32) ;; (macroexpand-1 '(nfx bar == (3 + foo) * quux )) ;; => (equal bar (* (+ 3 foo) quux)) ;; NOTE: detection of function calls ;; function call forms should be supported: ;; (macroexpand-1 '(nfx foo = (max (bar + 32) quux niaw) )) ;; => (setf foo (max (+ bar 32) quux niaw)) ;; (macroexpand-1 '(nfx (cdr foo) = (cons (qux + 1) nil))) ;; => (setf (cdr foo) (cons (+ qux 1) nil)) ;; If any infix notation is in a function call within an ;; nfx form, it should be within a parentheses: ;; (macroexpand-1 '(nfx (max (bar + foo) (quux + quuux)) )) ;; => (max (+ bar foo) (+ quux quuux)) ;; (macroexpand-1 '(nfx (max bar + foo quux + quuux) )) ;; => (max bar + foo quux + quuux) ;; function calls are detected in the following manner: ;; if nfx detects a list in the input stream, ;; if the second item is not a registered infix, ;; function call, for each element recurse and replace the element ;; not a function call, recurse on the list as a new stream ;; this allows us to use prefix operators (such as -) as-is: ;; (macroexpand-1 '(nfx (- bar) == (/ (foo + 1)) )) ;; => (equal (- bar) (/ (+ foo 1))) ;; (nfx-operator-base <action> ...) ;; Handles the operator database (let ((nfx-data (make-hash-table :test 'eq))) (defun nfx-operator-base (action &rest params) (labels ((getval (sym) (gethash sym nfx-data) ) (add (params) (setf (gethash (car params) nfx-data) (apply #'vector params)))) (case action (:get (getval (car params))) (:add (add params)))))) ;;; the nfx macro (defun nfx-impl (s) (let (opstack curop tmp (bldg (cons nil nil))) (labels ( ;; tconc = a cons with pointers to the head and the last element of ;; a list. This function appends an element to such a tconc. (tconc-append (l v) (if (car l) (setf (cdr l) (setf (cddr l) (cons v nil))) (setf (car l) (setf (cdr l) (cons v nil))) )) ;; top-of-stack query (top-opstack () (caaar opstack)) ;; handles any sub-lists (enlist (l) (when l (cond ((getop (cadr l)) (cons 'nfx l)) (t (mapcar #'(lambda (o) (if (listp o) (enlist o) o)) l))))) ;; pushes an operation onto the stack - used when the currently ;; being built operation is of lower precedence than the ;; operation being considered (push-oper () (push bldg opstack) (setf bldg (cons nil nil))) ;; pops off an operation from the stack, ;; - used before collapsing the call (pop-oper () (let ((top (pop opstack)) ) (tconc-append top (car bldg)) (setf bldg top))) ;; sub-expression handling code (expr (o) (if (listp o) (enlist o) o)) ;; determine if the specified operation has precedence over the ;; operation currently being built (precedes? (op1 op2 associativity) (or (< (precedence op1) (precedence op2)) (and (= (precedence op1) (precedence op2)) (eq (associativity op1) associativity)))) ;; funges bldg: collapses fungible operations into one form (fungebldg (bldg) (mapcan #'(lambda (o) (cond ((listp o) (setf o (fungebldg o)) (cond ((and (fungible (car bldg)) (eq (car o) (car bldg))) (cdr o)) (t (cons o nil)))) (t (cons o nil)))) bldg)) ;; fixes bldg: changes operation objects to their functions (fixbldg (bldg) (when (vectorp (car bldg)) (setf (car bldg) (function-name (car bldg))) ) (mapc #'(lambda (o) (when (listp o) (fixbldg o) )) bldg )) ;; error-handling function (err (l) (error "improper nfx expression:~%~s" l)) (print-expr-list (l) (format t "(") (loop :for x in l :for i from 0 :do (when (plusp i) (format t " ")) (cond ((vectorp x) (format t "~s" (aref x 0))) ((listp x) (print-expr-list x)) (t (format t "~s" x)))) (format t ")")) ;; (print-tconc (tc) ;; (print-expr-list (car tc)) ;; (format t "~%")) ;; accessor functions (precedence (op) (if op (aref op 1) 99999)) (associativity (op) (aref op 2)) (function-name (op) (aref op 3)) (fungible (op) (when (vectorp op) (aref op 4))) ;; get the data for a (presumed) infix operator (getop (op) (nfx-operator-base :get op))) (case (length s) (1 (expr (car s))) (2 (err s)) (t (do ( ;; variable and step list (oL s (cddr oL)) ) ( ;; termination condition (null (cddr oL)) (tconc-append bldg (expr (car oL))) (when (cdr oL) (err oL) ) (loop :while opstack :do (pop-oper)) (fixbldg (fungebldg (caar bldg)))) (setf curop (getop (cadr oL))) (cond (curop (cond ((precedes? curop (caar bldg) :right) (push-oper) (tconc-append bldg curop) (tconc-append bldg (expr (car oL))) ) (t (tconc-append bldg (expr (car oL))) ;; collapse while the stacktop is precedent over the ;; current op (loop :while (precedes? (top-opstack) curop :left) :do (pop-oper)) (setf tmp (car bldg)) (setf bldg (cons nil nil)) (tconc-append bldg curop) (tconc-append bldg tmp) ))) (t (err oL))))))))) (defmacro nfx (&rest s) (nfx-impl s)) ;; (definfix <operator> ;; :precedence <integer> ;; [:associativity <:left | :right>] ;; [:function-name <actual function>] ;; [:fungible <t | nil>]) ;; - defines an infix operator with the symbol <operator>, ;; with a precedence of <integer>. The smaller the precedence ;; number, the more precedence it has: * and / have smaller ;; precedence number than + and -. ;; - associativity defaults to :left, which means that if two ;; operators of the same precedence are encountered, the first ;; one resolves first: 1 x 2 x 3 becomes ((1 x 2) x 3). This ;; is appropriate for most maths. :right associativity means ;; that 1 x 2 x 3 becomes (1 x (2 x 3)). This is appropriate ;; for assignment. IMPORTANT: operators with the same ;; precedence must have the same associativities! ;; - function-name defaults to the same symbol as the operator. ;; For example, the function-name of = is setf. ;; - fungible means that if the same operator is encountered ;; several times, then all inputs are funged into one function ;; call. For example, 1 + 2 + 3 becomes (+ 1 2 3), 1 < 2 < 3 ;; becomes (< 1 2 3). This is not true for assignment: ;; x = y = z should become (setf x (setf y z)), not (setf x y z) ;; - fungible defaults to t because I noticed that nearly every ;; single darned operator was fungible. Except assignment. ;; Saved some dozen lines of code too. (defmacro definfix (operator &key precedence (associativity :left) function-name (fungible t)) `(nfx-operator-base :add ',operator ,precedence ,associativity ',(if function-name function-name operator ) ,fungible)) ;; Predefined operators ;; Note: precedences are divisibles of 10, in case you ;; want to insert precedence levels between levels. ;; since we expect infix notation only (not infix-postfix), ;; our array accessor is a single infix @ (definfix @ :precedence 10 :function-name aref) (definfix ** :precedence 20 :function-name expt) (definfix * :precedence 30) (definfix / :precedence 29) (definfix % :precedence 28 :function-name mod) (definfix + :precedence 40) (definfix - :precedence 40) (definfix <= :precedence 60) (definfix < :precedence 60) (definfix >= :precedence 60) (definfix > :precedence 60) (definfix = :precedence 70 :fungible nil) (definfix /= :precedence 70) ;; 80-100 should be for the bitwise operators (&, |, ^), ;; once I figure out how CL handles bitops. (definfix && :precedence 110 :function-name and) (definfix || :precedence 120 :function-name or) (set-dispatch-macro-character #\# #\n #'(lambda (stream c1 c2) (declare (ignorable c1 c2)) (let ((rd (read stream t nil t))) (if (listp rd) `(nfx ,@rd) (progn (print 'invalid-#n-usage) (print rd) (error 'error) ))))) ;; (nfx 55 - 3 * 4 + 2000000) used to give -1999957 ;; instead of the correct result 2000043. This is now corrected. -- Bruno Daniel

The program is in the public domain. A later version with an MIT license attached is here.