4. Bigloo -- Core Language

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Home: | Bigloo A ``practical Scheme compiler'' User manual for version 2.6b December 2003
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Core Language
4.1 | Syntax
| 4.1.1 | Comments
| 4.1.2 | Expressions
| 4.1.3 | Definitions
Chapters
| Acknowledgements
1. | Table of contents
2. | Overview of Bigloo
3. | Modules
4. | Core Language
5. | Standard Library
6. | Pattern Matching
7. | Object System
8. | Threads
9. | Regular parsing
10. | Lalr(1) parsing
11. | Errors and Assertions
12. | Eval and code interpretation
13. | Macro expansion
14. | Command Line Parsing
15. | Explicit typing
16. | The C interface
17. | The Java interface
18. | Bigloo Libraries
19. | Extending the Runtime System
20. | SRFIs
21. | DSSSL support
22. | Compiler description
23. | User Extensions
24. | Bigloo Development Environment
25. | Global Index
26. | Library Index
| Bibliography
| This chapter presents the Bigloo basics. It presents the elements that compose the body of a module (see Modules).
4.1 Syntax
The syntax of Bigloo is that of Scheme (a parenthesis based one) with two exceptions: type information and multi-line comments. Type information is supplied when identifiers are introduced (via `lambda`, `let`, `define`, ...) and those identifiers holding type information are referred to as typed identifiers. They are defined by the following grammar:
    <ident>        ==> <r5rs-ident> | <typed-ident>
    <typed-ident>  ==> <r5rs-ident>::<r5rs-ident>
    <r5rs-ident>   ==> the standard Scheme identifiers

For details of the standard Scheme identifiers, see info-file `r5rs.info', .
Multi-lines comments (see http://srfi.schemers.org/srfi-30/) are defined as:

    <ident>        ==> <r5rs-ident> | <typed-ident>
    <comment>      ==> ;<all subsequent characters up to a line break>
           	       | #| <comment-text> (<comment> <comment-text>)* |#
    <comment-text> ==> <character sequence not containing #| or |#>

### 4.1.1 Comments

Comments and whitespaces are the same as in r5rs, Whitespace and comments.

    ;;; The FACT procedure computes the factorial
    ;;; of a non-negative integer.
    (define fact
      (lambda (n)
        (if (= n 0)
            1        ;; Base case: return 1
            (* n (fact (- n 1))))))

### 4.1.2 Expressions

Bigloo expressions are the same as in r5rs, Expressions. Bigloo has more syntactic keywords than Scheme. The Bigloo syntactic keywords are:

    =>                      do                    or
    and                     else                  quasiquote
    begin                   if                    quote
    case                    lambda                set!
    cond                    let                   unquote
    unquote-splicing        define                let*
    delay                   letrec                module
    labels                  try                   define-struct
    unwind-protect          bind-exit             define-inline
    regular-grammar         lalr-grammar          regular-search
    define-expander         define-macro          match-case
    match-lambda            pragma                failure
    assert                  define-generic        define-method
    instantiate             duplicate             with-access
    widen!                  shrink!               multiple-value-bind
    let-syntax              letrec-syntax         define-syntax
    cond-expand             receive               args-parse
    define-record-type      and-let*

All other non atomic Bigloo forms are evaluated as functioncalls or macro class.

<variable> | syntax
quote datum | syntax
`'`datum | syntax
<constant> | syntax
    (define x 28)                          =>
    x                                      => 28
    (quote a)                              => A
    (quote #(a b c))                       => #(A B C)
    (quote (+ 1 2))                        => (+ 1 2)
    'a                                     => A
    '#(a b c)                              => #(A B C)
    '()                                    => ()
    '(+ 1 2)                               => (+ 1 2)
    '(quote a)                             => (QUOTE A)
    '"abc"                                 => "abc"
    "abc"                                  => "abc"
    '145932                                => 145932
    145932                                 => 145932
    '#t                                    => #t
    #t                                     => #t

operator operand ... | syntax
    (+ 3 4)                                => 7
    ((if #f + *) 3 4)                      => 12
    ((lambda (x) (+ 1 x)) 5)               => 6

lambda formals body | syntax
    (lambda (x) (+ x x))                   => a procedure
    ((lambda (x) (+ x x)) 4)               => 8

    (define reverse-subtract
      (lambda (x y) (- y x)))
    (reverse-subtract 7 10)                => 3

    (define add4
      (let ((x 4))
        (lambda (y) (+ x y))))
    (add4 6)                               => 10

    ((lambda x x) 3 4 5 6)                 => (3 4 5 6)
    ((lambda (x y . z) z)
     3 4 5 6)                              => (5 6)

if test consequent [alternate] | syntax
    (if (> 3 2) 'yes 'no)                  => yes
    (if (> 2 3) 'yes 'no)                  => no
    (if (> 3 2)
        (- 3 2)
        (+ 3 2))                           => 1

set! variable expression | syntax
    (define x 2)
    (+ x 1)                                => 3
    (set! x 4)                             => unspecified
    (+ x 1)                                => 5

cond clause clause ... | library syntax
    (cond ((> 3 2) 'greater)
          ((< 3 2) 'less))                 => greater

    (cond ((> 3 3) 'greater)
          ((< 3 3) 'less)
          (else 'equal))                   => equal

    (cond ((assv 'b '((a 1) (b 2))) => cadr)
          (else #f))                       => 2

case key clause clause ... | library syntax
    (case (* 2 3)
      ((2 3 5 7) 'prime)
      ((1 4 6 8 9) 'composite))            => composite
    (case (car '(c d))
      ((a) 'a)
      ((b) 'b))                            => unspecified
    (case (car '(c d))
      ((a e i o u) 'vowel)
      ((w y) 'semivowel)
      (else 'consonant))                   => consonant

and test ... | library syntax
    (and (= 2 2) (> 2 1))                  => #t
    (and (= 2 2) (< 2 1))                  => #f
    (and 1 2 'c '(f g))                    => (f g)
    (and)                                  => #t

and-let* test ... | bigloo syntax
In case of an ordinary `and` formed of proper boolean expressions: `(and e1 e2 ...)` expression `e2`, if it gets to be evaluated, knows that `e1` has returned non-`#f`. Moreover, `e2` knows exactly what the result of `e1` was -- `#t` -- which `e2` can use to its advantage. If `e1` however is an extended boolean expression, `e2` can no longer tell which particular non-`#f` value `e1` has returned. Chances are it took a lot of work to evaluate `e1`, and the produced result (a number, a vector, a string, etc) may be of value to `e2`. Alas, the `and` form merely checks that the result is not an `#f`, and throws it away. If `e2` needs it, it has to compute that value anew. This proposed `and-let*` special form lets constituent expressions get hold of the results of already evaluated expressions, without re-doing their work. `and-let*` can be thought of as a combination of `let*` and `and`, or a generalization of `cond`'s send operator `=>`. An `and-let*` form can also be considered a sequence of guarded expressions. In a regular program, forms may produce results, bind them to variables and let other forms use these results. `and-let*` differs in that it checks to make sure that every produced result "makes sense" (that is, not an `#f`). The first "failure" triggers the guard and aborts the rest of the sequence (which presumably would not make any sense to execute anyway).
    (and-let* ((x 1) (y 2)) (cons x y))    => (1 . 2)
    (and-let* ((x 1) (z #f)) x)            => #f

    (and-let* ((my-list (compute-list)) ((not (null? my-list))))
              (do-something my-list))

    (define (look-up key alist)
      (and-let* ((x (assq key alist))) (cdr x)))

    (or (and-let* ((c (read-char))
                   ((not (eof-object? c))))
                  (string-set! some-str i c)
                  (set! i (+ 1 i)))
Note: This documentation has been written by Oleg Kiselyov under the following copyright:
    Copyright (C) Oleg Kiselyov (1998). All Rights Reserved.

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    included on all such copies and derivative works. However, this
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or test ... | library syntax
    (or (= 2 2) (> 2 1))                   => #t
    (or (= 2 2) (< 2 1))                   => #t
    (or #f #f #f)                          => #f
    (or (memq 'b '(a b c))
        (/ 3 0))                           => (b c)

let [name] (binding ...) body | library syntax
    (let ((x 2) (y 3))
      (* x y))                             => 6

    (let ((x 2) (y 3))
      (let ((x 7)
            (z (+ x y)))
        (* z x)))                          => 35

    (let loop ((l '(1 2 3)))
       (if (null? l)
           '()
           (cons (+ 1 (car l))
                 (loop (cdr l)))))         => (2 3 4)

let* (binding ...) body | library syntax
    (let ((x 2) (y 3))
      (let* ((x 7)
             (z (+ x y)))
        (* z x)))                          => 70

letrec (binding ...) body | library syntax
    (letrec ((even?
              (lambda (n)
                (if (zero? n)
                    #t
                    (odd? (- n 1)))))
             (odd?
              (lambda (n)
                (if (zero? n)
                    #f
                    (even? (- n 1))))))
      (even? 88))
                                           => #t

labels ((name (arg ...) body) ...) body | bigloo syntax
The syntax is similar to the Common Lisp one [Steele90], where created bindings are immutable.
    (labels ((loop (f l acc)
                   (if (null? l)
                       (reverse! acc)
                       (loop f (cdr l) (cons (f (car l)) acc)))))
       (loop (lambda (x) (+ 1 x)) (list 1 2 3) '()))
       => (2 3 4)

begin expression expression ... | library syntax
    (define x 0)

    (begin (set! x 5)
           (+ x 1))                        => 6

    (begin (display "4 plus 1 equals ")
           (display (+ 4 1)))              => unspecified
                                           -| 4 plus 1 equals 5

do ((variable init step) ...) (test expression ...) body | library syntax
    (do ((vec (make-vector 5))
         (i 0 (+ i 1)))
        ((= i 5) vec)
      (vector-set! vec i i))               => #(0 1 2 3 4)

    (let ((x '(1 3 5 7 9)))
      (do ((x x (cdr x))
           (sum 0 (+ sum (car x))))
          ((null? x) sum)))                => 25

delay expression | library syntax

quasiquote template | syntax
``` template | syntax
    `(list ,(+ 1 2) 4)                     => (list 3 4)
    (let ((name 'a)) `(list ,name ',name))
              => (list a (quote a))
    `(a ,(+ 1 2) ,@(map abs '(4 -5 6)) b)
              => (a 3 4 5 6 b)
    `((foo ,(- 10 3)) ,@(cdr '(c)) . ,(car '(cons)))
              => ((foo 7) . cons)
    `#(10 5 ,(sqrt 4) ,@(map sqrt '(16 9)) 8)
              => #(10 5 2 4 3 8)
    `(a `(b ,(+ 1 2) ,(foo ,(+ 1 3) d) e) f)
              => (a `(b ,(+ 1 2) ,(foo 4 d) e) f)
    (let ((name1 'x)
          (name2 'y))
      `(a `(b ,,name1 ,',name2 d) e))
              => (a `(b ,x ,'y d) e)
    (quasiquote (list (unquote (+ 1 2)) 4))
              => (list 3 4)
    '(quasiquote (list (unquote (+ 1 2)) 4))
              => `(list ,(+ 1 2) 4)
         i.e., (quasiquote (list (unquote (+ 1 2)) 4))

### 4.1.3 Definitions

Global bindings are introduced by the `define` form:

define variable expression | syntax
define (variable arg ...) body | syntax
    (define add3
      (lambda (x) (+ x 3)))
    (add3 3)                               => 6
    (define first car)
    (first '(1 2))                         => 1

See r5rs, Definitions, for more details. The Bigloo module language (See Module Declaration) enables exports and imports of global definitions.

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Last update Tue Dec 16 13:46:41 2003