506 lines
18 KiB
Scheme
506 lines
18 KiB
Scheme
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;;; An awk loop, after the design of David Albertz and Olin Shivers.
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;;; Copyright (c) 1994 by Olin Shivers.
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;;; - Requires RECEIVE from RECEIVING package.
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;;; - Would require DESTRUCTURE from DESTRUCTURING package, but it appears
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;;; to be broken, so we hack it w/cars and cdrs.
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;;; - Requires STRING-MATCH from SCSH package.
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;;; This should be hacked to convert regexp strings into regexp structures
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;;; at the top of the form, and then just refer to the structs in the
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;;; tests.
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;;; Examples:
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;;
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;;; ;;; Filter -- pass only lines containing my name.
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;;; (awk (read-line) (line) ()
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;;; ("Olin" (display line) (newline)))
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;;;
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;;; ;;; Count the number of non-comment lines of code in my Scheme source.
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;;; (awk (read-line) (line) ((nlines 0))
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;;; ("^[ \t]*;" nlines) ; A comment line.
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;;; (else (+ nlines 1))) ; Not a comment line.
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;;;
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;;; ;;; Read numbers, counting the evens and odds.
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;;; (awk (read) (val) ((evens 0) (odds 0))
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;;; ((zero? val) (display "zero ") (values evens odds)) ; Tell me about
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;;; ((> val 0) (display "pos ") (values evens odds)) ; sign, too.
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;;; (else (display "neg ") (values evens odds))
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;;;
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;;; ((even? val) (values (+ evens 1) odds))
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;;; (else (values evens (+ odds 1))))
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;;; Syntax:
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;;; (awk <reader-exp> <rec&field-vars> [<rec-counter>] <state-var-inits>
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;;; <clause1>
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;;; .
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;;; .
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;;; <clausen>)
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;;; This macro is written using Clinger/Rees explicit-renaming low-level
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;;; macros. So it is pretty ugly. It takes a little care to generate
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;;; cosmetically attractive code, for two reasons:
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;;; - It makes it easier for humans to examine the expanded code.
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;;; - It helps low-tech compilers compile the code well. Some of the
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;;; optimisations the expander implements would be hard for even a
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;;; sophisticated compiler to perform automatically. For example, it doesn't
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;;; introduce a record-counter variable unless required to do so. It's a
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;;; non-trivial analysis to spot and remove an unused loop variable (I show
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;;; how to do so in my dissertation; I don't know of any production
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;;; compilers that do it). Same remarks apply to the variable that tracks
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;;; the state bit for ELSE clauses -- we don't introduce one unless the loop
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;;; actually contains ELSE clauses. The lesson here is that loop macros
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;;; by definition have information about the data-flow of their bodies that
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;;; compilers have to work hard to spot by analysis of their expanded forms.
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;;; The macro can exploit this knowledge at the high-level.
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;;;
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;;; Interesting research issue: Could one design a macro system that would
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;;; allow the macro to communicate this knowledge to the compiler? Could
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;;; the macro's assertions be verified by the compiler, as well?
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;;;
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;;; In any even, there's a down-side to this cosmetic clean-up:
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;;; all of this optimisation definitely makes the macro a lot more hairy
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;;; than it would otherwise be. The expanded code is easier to read; the
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;;; macro itself is harder to read.
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;;; Simple syntax-hacking utilities.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; Return a form that produces multiple values.
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;;; () => (values)
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;;; (v) => v
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;;; (v1 v2 ...) => (values v1 v2 ...)
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(define (mult-values vals rename)
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(if (or (not (pair? vals)) (pair? (cdr vals)))
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`(,(rename 'values) . ,vals)
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(car vals)))
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;;; () => ()
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;;; (v1) => (v1)
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;;; (v1 v2) => ((VALUES v1 v2))
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;;;
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;;; Return an expression list, not an expression. (Either 1 or 0 expressions.)
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;;; Use this one when we don't care what happens if we are returning 0 vals.
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;;; It pairs up with MV-LET below, which ignores the number of values
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;;; returned to it when expecting zero values.
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(define (sloppy-mult-values vals rename)
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(if (and (pair? vals) (pair? (cdr vals)))
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`((,(rename 'values) . ,vals))
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vals))
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;; DEBLOCK maps an expression to a list of expressions, flattening BEGINS.
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;; (deblock '(begin (begin 3 4) 5 6 (begin 7 8))) => (3 4 5 6 7 8)
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(define (deblock exp rename compare)
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(let ((%block (rename 'begin)))
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(let deblock1 ((exp exp))
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(if (and (pair? exp)
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; (name? (car exp))
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(compare %block (car exp)))
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(apply append (map deblock1 (cdr exp)))
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(list exp)))))
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;; BLOCKIFY maps an expression list to a BEGIN form, flattening nested BEGINS.
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;; (blockify '( (begin 3 4) 5 (begin 6) )) => (begin 3 4 5 6)
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(define (blockify exps rename compare)
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(let ((new-exps (apply append
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(map (lambda (exp) (deblock exp rename compare))
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exps))))
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(cond ((null? new-exps)
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(error "Empty BEGIN" exps))
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((null? (cdr new-exps)) ; (begin exp) => exp
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(car new-exps))
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(else `(,(rename 'begin) . ,new-exps)))))
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(define (mv-let r c vars exp body)
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(if (pair? vars)
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(if (pair? (cdr vars))
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`(,(r 'receive) ,vars ,exp . ,(deblock body r c))
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`(,(r 'let) ((,(car vars) ,exp)) . ,(deblock body r c)))
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(blockify (list exp body) r c)))
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;;; Is X one of the keywords {range, :range, range:, :range:}?
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(define (range-keyword? x rename compare)
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(or (compare x (rename 'range))
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(compare x (rename ':range))
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(compare x (rename 'range:))
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(compare x (rename ':range:))))
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;;; Apply PRED to every element of VALS. Collect & return all the non-#f
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;;; values produced.
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(define (all-trues pred vals)
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(let lp ((vals vals) (ans '()))
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(if (pair? vals)
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(lp (cdr vals)
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(cond ((pred (car vals)) => (lambda (elt) (cons elt ans)))
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(else ans)))
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(reverse ans))))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(define (expand-awk exp r c)
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(let* ((%lambda (r 'lambda)) ; Bind a mess of keywords.
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(%let (r 'let))
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(%receive (r 'receive))
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(%values (r 'values))
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(%if (r 'if))
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(%eof-object? (r 'eof-object?))
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(%after (r 'after))
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(%else (r 'else))
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(%+ (r '+))
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(gensym (let ((i 0))
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(lambda (s)
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(set! i (+ i 1))
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(string->symbol (string-append s (number->string i))))))
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;; Is the clause a range-test clause?
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(range? (lambda (clause) (range-keyword? (car clause) r c)))
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;; Make some standard vars we'll need.
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(lp-var (r 'lp))
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(reader (r 'read-rec))
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;; If I throw in an abort-loop or abort-iteration macro,
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;; I'll also need to make two vars for the continuations.
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;; Rip the form apart.
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(reader-exp (cadr exp))
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(rec/field-vars (caddr exp))
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(rec-var (car rec/field-vars)) ; The var bound to the record.
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(rest (cdddr exp))) ; Stuff after the rec&field-vars.
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(receive (rec-counter state-inits clauses) ; Parse out the last
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(if (list? (car rest)) ; three parts of the
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(values #f (car rest) (cdr rest)) ; form.
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(values (car rest) (cadr rest) (cddr rest)))
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;; Some analysis: what have we got?
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;; Range clauses, else clauses, line num tests,...
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(let* ((recnum-tests? ; Do any of the clauses test the record
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(any? (lambda (clause) ; count? (I.e., any integer tests?)
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(let ((test (car clause)))
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(or (integer? test)
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(and (range? clause)
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(or (integer? (cadr clause))
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(integer? (caddr clause)))))))
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clauses))
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;; If any ELSE clauses, bind this to the var in which we
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;; will keep the else state, otherwise #f.
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(else-var (and (any? (lambda (clause)
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(c (car clause) %else))
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clauses)
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(r 'elss)))
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;; Make a list of state vars for the range clauses.
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;; For each range clause, we need a boolean var to track
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;; whether or not the range is activated.
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(range-vars (all-trues (lambda (clause)
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(and (range? clause)
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(r (gensym "r."))))
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clauses))
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(svars (map car state-inits)) ; The user's state variables.
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;; If the user didn't declare a record-counter var,
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;; but he is testing line numbers (with integer test forms),
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;; go ahead and generate a record-counter of our own.
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(rec-counter (or rec-counter
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(and recnum-tests?
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(r (gensym "record-count.")))))
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;; Generate the loop vars & their inits.
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;; These are: the record counter, the range vars,
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;; and the user's state vars.
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;; All of these different sets are optional.
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(loop-vars (append (if rec-counter (list rec-counter) '())
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range-vars
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svars))
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(loop-var-init-values (append (if rec-counter '(0) '())
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(map (lambda (x) #f) range-vars)
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(map cadr state-inits)))
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;; A LET list initialising all the loop vars.
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(loop-var-init (map list loop-vars loop-var-init-values))
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;; Build the clause that computes the loop's return value.
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;; If the user gave an AFTER clause, use its body. Otherwise,
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;; it's (values ,@svars).
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(after-clause? (lambda (clause) (c (car clause) %after)))
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(after-exp (let ((after-clauses (filter after-clause? clauses)))
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(cond ((null? after-clauses)
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(mult-values svars r))
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((null? (cdr after-clauses))
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(blockify (cdar after-clauses) r c))
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(else (error "Multiple AFTER clauses in awk body."
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after-clauses exp)))))
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(loop-body (awk-loop-body lp-var rec-var else-var
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rec-counter range-vars svars
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clauses r c))
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;; Variables that have to be updated per-iteration, as a LET list.
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;; Note that we are careful not to increment the record counter
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;; until after we've verified the new record isn't EOF.
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(per-iteration-updates
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(append (if else-var `((,else-var #t)) '()) ; Else state.
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(if rec-counter ; Record count.
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`((,rec-counter (,%+ ,rec-counter 1)))
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'())))
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(loop-body (if (pair? per-iteration-updates)
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`(,%let ,per-iteration-updates
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. ,(deblock loop-body r c))
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loop-body)))
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`(,%let ((,reader (,%lambda () ,reader-exp)))
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(,%let ,lp-var ,loop-var-init
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,(mv-let r c rec/field-vars `(,reader)
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`(,%if (,%eof-object? ,rec-var) ,after-exp
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,loop-body))))))))
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;;; Expand into the body of the awk loop -- the code that tests & executes
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;;; each clause, and then jumps to the top of the loop.
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(define (awk-loop-body lp-var rec-var else-var rec-counter
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range-vars svars clauses r c)
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(let ((clause-vars (if else-var (cons else-var svars) svars))
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(loop-vars (append (if rec-counter (list rec-counter) '())
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range-vars
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svars))
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(range-clause? (lambda (clause) (range-keyword? (car clause) r c)))
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(%after (r 'after))
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(%else (r 'else)))
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(let expand ((clauses clauses) (range-vars range-vars))
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(if (pair? clauses)
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(let* ((clause (car clauses))
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(test (car clause)))
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(cond ((range-keyword? test r c)
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(let ((tail (expand (cdr clauses) (cdr range-vars))))
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(expand-range-clause clause tail (car range-vars)
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rec-var else-var rec-counter svars
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r c)))
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((c test %after) ; An AFTER clause. Skip it.
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(expand (cdr clauses) range-vars))
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((c test %else) ; An ELSE clause.
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(let ((tail (expand (cdr clauses) range-vars)))
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(expand-else-clause clause tail else-var svars r c)))
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(else ; A simple clause.
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(let ((tail (expand (cdr clauses) range-vars)))
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(expand-simple-clause clause tail
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rec-var else-var rec-counter svars
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r c)))))
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;; No clauses -- just jump to top of loop.
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`(,lp-var . ,loop-vars)))))
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;;; Make a Scheme expression out of a test form.
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;;; Integer i => (= i <record-counter>)
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;;; String s => (string-match s <record>)
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;;; Expression e => e
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(define (->simple-clause-test test-form rec-var rec-counter r)
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(cond ((integer? test-form) `(,(r '=) ,rec-counter ,test-form))
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((string? test-form) `(,(r 'string-match) ,test-form ,rec-var))
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(else test-form)))
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(define (expand-simple-clause clause tail
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rec-var else-var rec-counter svars
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r c)
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(let* ((%let (r 'let))
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(%= (r '=))
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(%string-match (r 'string-match))
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(%arrow (r '=>))
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(%if (r 'if))
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(test (car clause))
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(test (->simple-clause-test test rec-var rec-counter r))
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;; Is clause of the form (test => proc)
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(arrow? (and (= 3 (length clause))
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(c (cadr clause) %arrow)))
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(null-clause-list (null-clause-action else-var svars r))
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;; The core form conditionally executes the body.
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;; It returns the new else var and the new state vars, if any.
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(core (if arrow?
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(let* ((tv (r 'tval)) ; APP is the actual
|
||
|
|
(app `(,(caddr clause) ,tv))) ; body: (proc tv).
|
||
|
|
`(,%let ((,tv ,test))
|
||
|
|
(,%if ,tv
|
||
|
|
,(clause-action (list app) else-var svars r c)
|
||
|
|
. ,null-clause-list)))
|
||
|
|
|
||
|
|
`(,%if ,test ,(clause-action (cdr clause) else-var svars r c)
|
||
|
|
. ,null-clause-list)))
|
||
|
|
|
||
|
|
(loop-vars (if else-var (cons else-var svars) svars)))
|
||
|
|
|
||
|
|
;; Do the core computation, update the iteration vars,
|
||
|
|
;; and then do the tail in the scope of the updated environment.
|
||
|
|
(core-then-tail loop-vars core tail r c)))
|
||
|
|
|
||
|
|
(define (core-then-tail loop-vars core tail r c)
|
||
|
|
(mv-let r c loop-vars core tail))
|
||
|
|
|
||
|
|
(define (expand-range-clause clause tail range-var
|
||
|
|
rec-var else-var rec-counter svars
|
||
|
|
r c)
|
||
|
|
(let* ((start-test (cadr clause))
|
||
|
|
(stop-test (caddr clause))
|
||
|
|
(body (cdddr clause))
|
||
|
|
|
||
|
|
(%receive (r 'receive))
|
||
|
|
(%if (r 'if))
|
||
|
|
(%lambda (r 'lambda))
|
||
|
|
|
||
|
|
(keyword (car clause)) ; range or :range or range: or :range:
|
||
|
|
(tester (r (cond ((c keyword (r 'range)) 'next-range)
|
||
|
|
((c keyword (r ':range)) 'next-:range)
|
||
|
|
((c keyword (r 'range:)) 'next-range:)
|
||
|
|
((c keyword (r ':range:)) 'next-:range:)
|
||
|
|
(else (error "Unrecognised range keyword!" clause)))))
|
||
|
|
|
||
|
|
;; Convert the start and stop test forms to code.
|
||
|
|
(start-test (->simple-clause-test start-test rec-var rec-counter r))
|
||
|
|
(stop-test (->simple-clause-test stop-test rec-var rec-counter r))
|
||
|
|
|
||
|
|
(start-thunk `(,%lambda () ,start-test)) ; ...and thunkate them.
|
||
|
|
(stop-thunk `(,%lambda () ,stop-test))
|
||
|
|
|
||
|
|
(loop-vars (if else-var (cons else-var svars) svars))
|
||
|
|
(this-rec (r 'this-record?))
|
||
|
|
|
||
|
|
(core `(,%if ,this-rec
|
||
|
|
,(clause-action body else-var svars r c)
|
||
|
|
. ,(null-clause-action else-var svars r))))
|
||
|
|
|
||
|
|
`(,%receive (,this-rec ,range-var)
|
||
|
|
(,tester ,start-thunk ,stop-thunk ,range-var)
|
||
|
|
,(core-then-tail loop-vars core tail r c))))
|
||
|
|
|
||
|
|
|
||
|
|
(define (expand-else-clause clause tail else-var svars r c)
|
||
|
|
(let* ((body (cdr clause))
|
||
|
|
(tail-exps (deblock tail r c))
|
||
|
|
|
||
|
|
(%if (r 'if))
|
||
|
|
(%receive (r 'receive))
|
||
|
|
(%let (r 'let))
|
||
|
|
|
||
|
|
;; We are hard-wiring the else var to #t after this, so the core
|
||
|
|
;; expression doesn't need to return it -- just the new values
|
||
|
|
;; of the user's state vars.
|
||
|
|
(core `(,%if ,else-var
|
||
|
|
,(clause-action body #f svars r c)
|
||
|
|
. ,(sloppy-mult-values svars r))))
|
||
|
|
|
||
|
|
(mv-let r c svars core `(,%let ((,else-var #t)) . ,tail-exps))))
|
||
|
|
|
||
|
|
|
||
|
|
;;; BODY is a list of expressions from a loop clause. We want to evaluate it,
|
||
|
|
;;; under some conditions.
|
||
|
|
;;; - The body evaluates to multiple values, one for each state variable.
|
||
|
|
;;; However, if there are no state variables, we want to *ignore* the
|
||
|
|
;;; values produced by the body, and explicitly return 0 values,
|
||
|
|
;;; not blow up if the body should happen not to return exactly zero values.
|
||
|
|
;;; - If we are tracking an else-variable, then the body firing will turn
|
||
|
|
;;; it off by returning its new #f value.
|
||
|
|
|
||
|
|
(define (clause-action body else-var svars r c)
|
||
|
|
(let ((%values (r 'values))
|
||
|
|
(%receive (r 'receive)))
|
||
|
|
|
||
|
|
(blockify (if (pair? svars)
|
||
|
|
|
||
|
|
(if else-var
|
||
|
|
(if (cdr svars) ; We've got state vars and an else var.
|
||
|
|
`((,%receive ,svars ,(blockify body r c)
|
||
|
|
(,%values #f . ,svars)))
|
||
|
|
`((,%values #f ,(blockify body r c)))) ; Gratuitous.
|
||
|
|
body) ; State vars, but no else var.
|
||
|
|
|
||
|
|
;; No state vars -- ignore value computed by BODY forms.
|
||
|
|
`(,@body . ,(if else-var '(#f) `())))
|
||
|
|
r c)))
|
||
|
|
|
||
|
|
|
||
|
|
;;; The clause didn't execute. Return the svars unchanged, and also
|
||
|
|
;;; return the current else-value if we are tracking one. We return
|
||
|
|
;;; a 0 or 1 element expression list -- if no values are being expected
|
||
|
|
;;; this returns the empty list.
|
||
|
|
|
||
|
|
(define (null-clause-action else-var svars r)
|
||
|
|
(sloppy-mult-values (if else-var (cons else-var svars) svars)
|
||
|
|
r))
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
;;; These procs are for handling RANGE clauses.
|
||
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||
|
|
;;; First return value tells whether this line is active;
|
||
|
|
;;; next value tells whether region is active after this line.
|
||
|
|
;;;
|
||
|
|
;;; (:range 0 4) = 0 1 2 3 This is the most useful one.
|
||
|
|
;;; (range: 0 4) = 1 2 3 4
|
||
|
|
;;; (range 0 4) = 1 2 3
|
||
|
|
;;; (:range: 0 4) = 0 1 2 3 4
|
||
|
|
|
||
|
|
;;; If these were inlined and the test thunks substituted, it would
|
||
|
|
;;; be acceptably efficient. But who writes Scheme compilers that good
|
||
|
|
;;; in the 90's?
|
||
|
|
|
||
|
|
(define (next-:range start-test stop-test state)
|
||
|
|
(let ((new-state (if state
|
||
|
|
(or (not (stop-test)) ; Stop,
|
||
|
|
(start-test)) ; but restart.
|
||
|
|
|
||
|
|
(and (start-test) ; Start,
|
||
|
|
(not (stop-test)))))) ; but stop, too.
|
||
|
|
(values new-state new-state)))
|
||
|
|
|
||
|
|
(define (next-range: start-test stop-test state)
|
||
|
|
(values state
|
||
|
|
(if state
|
||
|
|
(or (not (stop-test)) ; Stop,
|
||
|
|
(start-test)) ; but restart.
|
||
|
|
(and (start-test) ; Start,
|
||
|
|
(not (stop-test)))))) ; but stop, too.
|
||
|
|
|
||
|
|
(define (next-range start-test stop-test state)
|
||
|
|
(if state
|
||
|
|
(let ((not-stop (not (stop-test))))
|
||
|
|
(values not-stop
|
||
|
|
(or not-stop ; Stop,
|
||
|
|
(start-test)))) ; but restart.
|
||
|
|
(values #f
|
||
|
|
(and (start-test) ; Start,
|
||
|
|
(not (stop-test)))))) ; but stop, too.
|
||
|
|
|
||
|
|
(define (next-:range: start-test stop-test state)
|
||
|
|
(if state
|
||
|
|
(values #t
|
||
|
|
(or (not (stop-test)) ; Stop
|
||
|
|
(start-test))) ; but restart.
|
||
|
|
|
||
|
|
(let ((start? (start-test)))
|
||
|
|
(values start?
|
||
|
|
(and start? ; Start,
|
||
|
|
(not (stop-test))))))) ; but stop, too.
|