New, improved let-opt. More features.
But I have a whole different design for handling optional args, so this will all go away at some point.
This commit is contained in:
olin-shivers
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commit
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673
scsh/let-opt.scm
673
scsh/let-opt.scm
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@ -1,24 +1,23 @@
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;;; LET-OPTIONALS macros
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;;; Copyright (c) 2001 by Olin Shivers.
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;;; See file COPYING.
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;;; This file defines three macros for parsing optional arguments to procs:
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;;; (LET-OPTIONALS arg-list ((var1 default1) ...) . body)
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;;; (LET-OPTIONALS* arg-list ((var1 default1) ...) . body)
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;;; (:OPTIONAL rest-arg default-exp)
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;;; (LET-OPTIONALS arg-list (opt-clause1 ... opt-clauseN [rest])
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;;; body ...)
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;;; (LET-OPTIONALS* arg-list (opt-clause1 ... opt-clauseN [rest])
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;;; body ...)
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;;; (:OPTIONAL rest-arg default-exp [arg-check])
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;;; where
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;;; <opt-clause> ::= (var default [arg-check supplied?])
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;;; | ((var1 ... varN) external-arg-parser)
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;;;
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;;; The LET-OPTIONALS macro is defined using the Clinger/Rees
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;;; explicit-renaming low-level macro system. You'll have to do some work to
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;;; port it to another macro system.
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;;; LET-OPTIONALS* has LET* scope -- each arg clause sees the bindings of
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;;; the previous clauses. LET-OPTIONALS has LET scope -- each arg clause
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;;; sees the outer scope (an ARG-CHECK expression sees the outer scope
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;;; *plus* the variable being bound by that clause, by necessity).
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;;;
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;;; The LET-OPTIONALS* and :OPTIONAL macros are defined with simple
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;;; high-level macros, and should be portable to any R4RS system.
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;;;
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;;; These macros are all careful to evaluate their default forms *only* if
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;;; their values are needed.
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;;;
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;;; The top-level forms in this file are Scheme 48 module expressions.
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;;; I use the module system to help me break up the expander code for
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;;; LET-OPTIONALS into three procedures, which makes it easier to understand
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;;; and test. But if you wanted to port this code to a module-less Scheme
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;;; system, you'd probably have to inline the three procs into the actual
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;;; macro definition.
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;;; In practice, LET-OPTIONALS* is the one you want.
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;;;
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;;; The only interesting module that is exported by this file is
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;;; LET-OPT
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@ -27,19 +26,41 @@
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;;; (let-optionals* :syntax)
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;;; (:optional :syntax))
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;;;
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;;; The LET-OPTIONALS macro is defined using the Clinger/Rees
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;;; explicit-renaming low-level macro system. You'll have to do some work to
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;;; port it to another macro system.
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;;;
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;;; The :OPTIONAL macro is defined with simple high-level macros,
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;;; and should be portable to any R4RS system.
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;;;
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;;; These macros are all careful to evaluate their default forms *only* if
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;;; their values are needed.
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;;;
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;;; The LET-OPTIONALS expander is pretty hairy. Sorry. It does produce
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;;; very good code.
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;;;
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;;; The top-level forms in this file are Scheme 48 module expressions.
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;;; I use the module system to help me break up the expander code for
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;;; LET-OPTIONALS into three procedures, which makes it easier to understand
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;;; and test. But if you wanted to port this code to a module-less Scheme
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;;; system, you'd probably have to inline the auxiliary procs into the actual
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;;; macro definition.
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;;;
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;;; To repeat: This code is not simple Scheme code; it is module code.
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;;; It must be loaded into the Scheme 48 ,config package, not the ,user
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;;; package.
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;;;
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;;; The only non-R4RS dependencies in the macros are ERROR
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;;; The only non-R4RS dependencies in the macros are ERROR, RECEIVE,
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;;; and CALL-WITH-VALUES.
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;;;
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;;; See below for details on each macro.
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;;; -Olin
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;;; (LET-OPTIONALS arg-list ((var1 default1) ...)
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;;; body
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;;; ...)
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;;; (LET-OPTIONALS* arg-list (clause ... [rest]) body ...)
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;;; (LET-OPTIONALS arg-list (clause ... [rest]) body ...)
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;;;
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;;; clause ::= (var default [arg-test supplied?]) ; The simple case
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;;; | ((var1 ...) external-arg-parser) ; external hook
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; This form is for binding a procedure's optional arguments to either
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;;; the passed-in values or a default.
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@ -49,22 +70,68 @@
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;;; the remaining VARi are bound to their corresponding DEFAULTi values.
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;;; It is an error if there are more args than variables.
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;;;
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;;; Simple example:
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;;; (let-optionals* args ((in (current-input-port))
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;;; (out (current-output-port))
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;;; (nbytes (string-length s)))
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;;; ...)
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;;;
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;;; - The default expressions are *not* evaluated unless needed.
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;;;
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;;; - When evaluated, the default expressions are carried out in the *outer*
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;;; environment. That is, the DEFAULTi forms do *not* see any of the VARi
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;;; bindings.
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;;; - When a LET-OPTIONALS* form is evaluated, the default expressions are
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;;; carried out in a "sequential" LET*-style scope -- each clause is
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;;; evaluated in a scope that sees the bindings introduced by the previous
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;;; clauses.
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;;;
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;;; I originally wanted to have the DEFAULTi forms get eval'd in a LET*
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;;; style scope -- DEFAULT3 would see VAR1 and VAR2, etc. But this is
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;;; impossible to implement without side effects or redundant conditional
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;;; tests. If I drop this requirement, I can use the efficient expansion
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;;; shown below. If you need LET* scope, use the less-efficient
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;;; LET-OPTIONALS* form defined below.
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;;; - LET-OPTIONALS, in contrast, evaluates all clauses in the *outer*
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;;; environment. Each ARG-TEST form, however, does see the variable
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;;; bound by that clause (see below).
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;;;
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;;; - If there's an ARG-TEST form, it is evaluated when an argument is
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;;; passed in; it is not evaluated when the argument is defaulted.
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;;; If it produces false, an error is raised. You can stick an arg-checking
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;;; expression here. Here's the above example with full arg-checking:
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;;; (let ((strlen (string-length s)))
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;;; (let-optionals args ((in (current-input-port) (input-port? in))
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;;; (out (current-output-port) (output-port? out))
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;;; (nbytes strlen (and (integer? nbytes)
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;;; (< -1 nbytes strlen))))
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;;; ...))
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;;;
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;;; The ARG-TEST expression is evaluated in the outer scope of the LET,
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;;; plus a binding for the parameter being checked.
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;;;
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;;; - A SUPPLIED? variable is bound to true/false depending on whether or
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;;; not a value was passed in by the caller for this parameter.
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;;;
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;;; - If there's a final REST variable in the binding list, it is bound
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;;; to any leftover unparsed values from ARG-LIST. If there isn't a final
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;;; REST var, it is an error to have extra values left. You can use this
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;;; feature to parse a couple of arguments with LET-OPTIONALS, and handle
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;;; following args with some other mechanism. It is also useful for
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;;; procedures whose final arguments are homogeneous.
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;;;
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;;; - A clause of the form ((var1 ... varn) external-arg-parser) allows you
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;;; to parse & arg-check a group of arguments together. EXTERNAL-ARG-PARSER
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;;; is applied to the argument list. It returns n+1 values: one
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;;; for the leftover argument list, and one for each VARi.
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;;;
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;;; This facility is intended for things like substring start/end index
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;;; pairs. You can abstract out the code for parsing the pair of arguments
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;;; in a separate procedure (parse-substring-index-args args string proc)
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;;; and then a function such as READ-STRING! can simply invoke the procedure
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;;; with a
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;;; ((start end) (lambda (args) (parse-substring-index-args args s read-string!)))
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;;; clause. That is, the external-arg parser facility is a hook
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;;; that lets you interface other arg parsers into LET-OPTIONALS.
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;;; Expanding the form
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;;;;;;;;;;;;;;;;;;;;;;
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;;; We expand the form into a code DAG that avoids repeatedly testing the
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;;; arg list once it runs out, but still shares code. For example,
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;;;
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;;; Example:
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;;; (define (read-string! str . maybe-args)
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;;; (let-optionals maybe-args ((port (current-input-port))
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;;; (let-optionals* maybe-args ((port (current-input-port))
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;;; (start 0)
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;;; (end (string-length str)))
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;;; ...))
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@ -72,107 +139,316 @@
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;;; expands to:
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;;;
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;;; (let* ((body (lambda (port start end) ...))
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;;; (end-def (lambda (%port %start) (body %port %start <end-default>)))
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;;; (start-def (lambda (%port) (end-def %port <start-default>)))
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;;; (end-def (lambda (port start) (body port start <end-default>)))
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;;; (start-def (lambda (port) (end-def port <start-default>)))
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;;; (port-def (lambda () (start-def <port-def>))))
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;;; (if (null? rest) (port-def)
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;;; (let ((%port (car rest))
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;;; (rest (cdr rest)))
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;;; (if (null? rest) (start-def %port)
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;;; (let ((%start (car rest))
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;;; (rest (cdr rest)))
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;;; (if (null? rest) (end-def %port %start)
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;;; (let ((%end (car rest))
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;;; (rest (cdr rest)))
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;;; (if (null? rest) (body %port %start %end)
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;;; (error ...)))))))))
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;;; (if (pair? tail)
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;;; (let ((port (car tail))
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;;; (tail (cdr tail)))
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;;; (if (pair? tail)
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;;; (let ((start (car tail))
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;;; (tail (cdr tail)))
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;;; (if (pair? tail)
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;;; (let ((end (car tail))
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;;; (tail (cdr tail)))
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;;; (if (pair? tail)
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;;; (error ...)
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;;; (body port start end)))
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;;; (end-def port start)))
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;;; (start-def port)))
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;;; (port-def)))
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;;;
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;;; Note that the defaulter code (the chain of ...-DEF procs) is just a
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;;; linear sequence of machine code into which the IF-tree branches. Once
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;;; we jump into the defaulter chain, we never test the arg list again.
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;;; A reasonable compiler can turn this into optimal parameter-parsing code.
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(define-structure let-opt-expanders (export expand-let-optionals)
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(open scheme)
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(define-structure let-opt-expanders (export expand-let-optionals
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expand-let-optionals*)
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(open scheme
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error-package
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receiving)
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(begin
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(define (make-gensym prefix)
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(let ((counter 0))
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(lambda ()
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(set! counter (+ counter 1))
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(string->symbol (string-append prefix (number->string counter))))))
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;;; This guy makes the END-DEF, START-DEF, PORT-DEF definitions above.
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;;; If an elt of VARS is a list, we are dealing with a group-parser clause.
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;;; In this case, the corresponding element of DEFS is the name of
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;;; the parser.
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;;; I wish I had a reasonable loop macro.
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;;;
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;;; DEFAULTER-NAMES also holds the xparser expressions
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;;; - STAR? true
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;;; LET* scope semantics -- default I & xparser I are evaluated in
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;;; a scope that sees vars 1 ... I-1.
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;;; - STAR? false
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;;; LET scope semantics -- default and xparser forms don't see any of the
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;;; vars.
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;;;
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;;; I considered documenting this procedure better, but finally decided
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;;; that if it was this hard for me to write, it should be hard for you
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;;; to read. -Olin
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(define (make-default-procs vars body-proc defaulter-names defs rename)
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(let ((%lambda (rename 'lambda)))
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(let recur ((vars (reverse vars))
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(defaulter-names (reverse defaulter-names))
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(defs (reverse defs))
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(next-guy body-proc))
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(if (null? vars) '()
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(let ((vars (cdr vars)))
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`((,(car defaulter-names)
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(,%lambda ,(reverse vars)
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(,next-guy ,@(reverse vars) ,(car defs))))
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. ,(recur vars
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(cdr defaulter-names)
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(cdr defs)
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(car defaulter-names))))))))
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(define (make-default-procs vars body-proc defaulter-names defs
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sup-vars rest-var star? rename)
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(receive (defaulters ignore-me and-me-too)
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(really-make-default-procs vars body-proc defaulter-names defs
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sup-vars rest-var star? rename)
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(reverse defaulters)))
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(define (really-make-default-procs vars body-proc defaulter-names defs
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sup-vars rest-var star? rename)
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(let ((%lambda (rename 'lambda))
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(%let (rename 'let))
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(%ignore (rename '_))
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(%call/values (rename 'call-with-values))
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(tail (rename 'tail))
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(make-rv (let ((g (make-gensym "%ov.")))
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(lambda x (rename (g)))))
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(make-sv (let ((g (make-gensym "%sv.")))
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(lambda () (rename (g))))))
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;; RECUR returns 2 values: a LET*-binding list of defaulter proc
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;; bindings, and an expression to evaluate in their scope.
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(let recur ((vars vars)
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(rev-params '()) ; These guys
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(rev-vals '()) ; have these values.
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(sup-vars sup-vars)
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(rev-sup-params '()) ; These guys
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(rev-sup-vals '()) ; have these values.
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(defaulter-names defaulter-names)
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(defs defs))
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;; Note that the #F's bound to the SUPPLIED? parameters have no
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;; effects, and so commute with the evaluation of the defaults.
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;; Hence we don't need the VALS-EVALED? trick for them, just for the
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;; default forms & their parameters.
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(if (pair? vars)
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(let* ((var (car vars)) (vars (cdr vars)) ; "VAR" is really a list
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(def (car defs)) (defs (cdr defs)) ; in xparser case...
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(rvar (if star? var ; scope control
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(if (pair? var) (map make-rv var) (make-rv))))
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(rev-params1 (if (pair? rvar)
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(append (reverse rvar) rev-params)
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(cons rvar rev-params)))
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(rev-vals1 (if (pair? rvar) rev-params1
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(cons def rev-params)))
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(sv (car sup-vars))
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(sv (if (or star? (not sv)) sv (make-sv)))
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(rev-sup-params1 (if sv (cons sv rev-sup-params)
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rev-sup-params))
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(rev-sup-vals1 (cond (sv (cons #f rev-sup-params))
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((pair? var) rev-sup-vals)
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(else rev-sup-params)))
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(defaulter (car defaulter-names))
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(defaulter-names (cdr defaulter-names)))
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(receive (procs exp vals-evaled?)
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(recur vars rev-params1 rev-vals1 (cdr sup-vars)
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rev-sup-params1 rev-sup-vals1
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defaulter-names defs)
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(if (pair? var)
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;; Return #f for VALS-EVALED? so we'll force any prior
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;; default to be eval'd & not pushed below this default eval.
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(values procs
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`(,%call/values (,%lambda () (,defaulter '()))
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(,%lambda ,(cons %ignore rvar) ,exp))
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#f)
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(let ((params (reverse (append rev-sup-params rev-params)))
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(exp (if vals-evaled? exp
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`(,%let ((,rvar ,def)) ,exp))))
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(values `((,defaulter (,%lambda ,params ,exp))
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. ,procs)
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`(,defaulter ,@(reverse rev-vals)
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,@(reverse rev-sup-vals))
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#t)))))
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(values '() `(,body-proc ,@(if rest-var '('()) '())
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,@(reverse rev-vals)
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. ,(reverse rev-sup-vals))
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#t)))))
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;;; This guy makes the (IF (NULL? REST) (PORT-DEF) ...) tree above.
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;;; This guy makes the (IF (PAIR? TAIL) ... (PORT-DEF)) tree above.
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;;; DEFAULTERS is a list of the names of the defaulter procs & the xparser
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;;; forms.
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(define (make-if-tree vars defaulters body-proc rest rename)
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(define (make-if-tree vars defaulters arg-tests body-proc
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tail supvars rest-var star? rename)
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(let ((%if (rename 'if))
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(%null? (rename 'null?))
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(%pair? (rename 'pair?))
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(%not (rename 'not))
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(%error (rename 'error))
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(%let (rename 'let))
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(%lambda (rename 'lambda))
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(%call/values (rename 'call-with-values))
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(%car (rename 'car))
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(%cdr (rename 'cdr)))
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(%cdr (rename 'cdr))
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(make-rv (let ((g (make-gensym "%ov.")))
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(lambda x (rename (g))))))
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(let recur ((vars vars) (defaulters defaulters) (non-defaults '()))
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(let recur ((vars vars) (defaulters defaulters)
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(ats arg-tests) (non-defaults '())
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(supvars supvars) (sup-trues '()))
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(if (null? vars)
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`(,%if (,%null? ,rest) (,body-proc . ,(reverse non-defaults))
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(,%error "Too many optional arguments." ,rest))
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(if rest-var
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`(,body-proc ,tail ,@(reverse non-defaults) . ,sup-trues)
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`(,%if (,%pair? ,tail)
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(,%error "Too many optional arguments." ,tail)
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(,body-proc ,@(reverse non-defaults) . ,sup-trues)))
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(let ((v (car vars)))
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`(,%if (,%null? ,rest)
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(,(car defaulters) . ,(reverse non-defaults))
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(,%let ((,v (,%car ,rest))
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(,rest (,%cdr ,rest)))
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(let* ((v (car vars))
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(rv (if star? v ; Scope control
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(if (pair? v) (map make-rv v) (make-rv))))
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(at (car ats))
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(sup-trues1 (if (car supvars) (cons #t sup-trues) sup-trues))
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(body `(,@(if (not (eq? at #t))
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(let ((test (if star? at
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`(,%let ((,v ,rv)) ,at))))
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`((,%if (,%not ,test)
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(,%error "Optional argument failed test"
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',at ',v ,rv))))
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'()) ; No arg test
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,(recur (cdr vars)
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(cdr defaulters)
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(cons v non-defaults)))))))))
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(cdr ats)
|
||||
(if (pair? rv)
|
||||
(append (reverse rv) non-defaults)
|
||||
(cons rv non-defaults))
|
||||
(cdr supvars) sup-trues1))))
|
||||
(if (pair? rv)
|
||||
`(,%call/values (,%lambda ()
|
||||
(,(car defaulters) ,tail))
|
||||
(,%lambda (,tail . ,rv) . ,body))
|
||||
|
||||
`(,%if (,%pair? ,tail)
|
||||
(,%let ((,rv (,%car ,tail))
|
||||
(,tail (,%cdr ,tail)))
|
||||
. ,body)
|
||||
(,(car defaulters) ,@(reverse non-defaults) . ,sup-trues))))))))
|
||||
|
||||
|
||||
(define (expand-let-optionals exp rename compare?)
|
||||
;;; Parse the clauses into
|
||||
;;; - a list of vars,
|
||||
;;; - a list of defaults,
|
||||
;;; - a list of possible arg-tests. No arg-test is represented as #T.
|
||||
;;; - a list of possible SUPPLIED? vars. An elt is either (var) or #f.
|
||||
;;; - either the rest var or #f
|
||||
;;;
|
||||
;;; This is written out in painful detail so that we can do a lot of
|
||||
;;; syntax checking.
|
||||
|
||||
(define (parse-clauses bindings)
|
||||
;; LIST-LIB defines EVERY... but uses LET-OPTIONALS.
|
||||
;; Define here to break the dependency loop:
|
||||
(define (every pred lis)
|
||||
(or (not (pair? lis)) (and (pred (car lis)) (every pred (car lis)))))
|
||||
|
||||
(cond ((pair? bindings)
|
||||
(let ((rev (reverse bindings)))
|
||||
(receive (rest-var rev) (if (symbol? (car rev))
|
||||
(values (car rev) (cdr rev))
|
||||
(values #f rev))
|
||||
(receive (vars defs ats supvars)
|
||||
(let recur ((bindings (reverse rev)))
|
||||
(if (not (pair? bindings))
|
||||
(values '() '() '() '())
|
||||
(receive (vars defs ats supvars) (recur (cdr bindings))
|
||||
(let ((binding (car bindings)))
|
||||
(if (not (and (list? binding) (<= 2 (length binding) 4)))
|
||||
(error "Illegal binding form in LET-OPTIONAL or LET-OPTIONAL*"
|
||||
binding))
|
||||
|
||||
(let* ((var (car binding))
|
||||
(vars (cons var vars))
|
||||
(defs (cons (cadr binding) defs))
|
||||
(stuff (cddr binding)))
|
||||
(if (not (or (symbol? var)
|
||||
(and (list? var)
|
||||
(= 2 (length binding))
|
||||
(every symbol? var))))
|
||||
(error "Illegal parameter in LET-OPTIONAL or LET-OPTIONAL* binding"
|
||||
binding))
|
||||
(receive (at sup-var)
|
||||
(if (not (pair? stuff)) (values #t #f)
|
||||
(let ((at (car stuff))
|
||||
(stuff (cdr stuff)))
|
||||
(if (not (pair? stuff))
|
||||
(values at #f)
|
||||
(let ((sv (car stuff)))
|
||||
(if (not (symbol? sv))
|
||||
(error "Illegal SUPPLIED? parameter in LET-OPTIONAL or LET-OPTIONAL*"
|
||||
binding sv))
|
||||
(values at sv)))))
|
||||
(values vars defs (cons at ats) (cons sup-var supvars))))))))
|
||||
(values vars defs ats supvars rest-var)))))
|
||||
|
||||
((null? bindings) (values '() '() '() '() #f))
|
||||
(else (error "Illegal bindings to LET-OPTIONAL or LET-OPTIONAL* form"
|
||||
bindings))))
|
||||
|
||||
(define (really-expand-let-optionals exp star? rename compare?)
|
||||
(let* ((arg-list (cadr exp))
|
||||
(var/defs (caddr exp))
|
||||
(body (cdddr exp))
|
||||
(vars (map car var/defs))
|
||||
|
||||
(prefix-sym (lambda (prefix sym)
|
||||
(string->symbol (string-append prefix (symbol->string sym)))))
|
||||
|
||||
;; Private vars, one for each user var.
|
||||
;; We prefix the % to help keep macro-expanded code from being
|
||||
;; too confusing.
|
||||
(vars2 (map (lambda (v) (rename (prefix-sym "%" v)))
|
||||
vars))
|
||||
|
||||
(defs (map cadr var/defs))
|
||||
(body-proc (rename 'body))
|
||||
|
||||
;; A private var, bound to the value of the ARG-LIST expression.
|
||||
(rest-var (rename '%rest))
|
||||
(tail-var (rename '%tail)) ; Bound to remaining args to be parsed.
|
||||
|
||||
(%let* (rename 'let*))
|
||||
(%lambda (rename 'lambda))
|
||||
|
||||
(defaulter-names (map (lambda (var) (rename (prefix-sym "def-" var)))
|
||||
vars))
|
||||
(prefix-sym (lambda (prefix sym)
|
||||
(string->symbol (string-append prefix (symbol->string sym))))))
|
||||
|
||||
(defaulters (make-default-procs vars2 body-proc
|
||||
defaulter-names defs rename))
|
||||
(if-tree (make-if-tree vars2 defaulter-names body-proc
|
||||
rest-var rename)))
|
||||
(receive (vars defs arg-tests maybe-supvars maybe-rest)
|
||||
(parse-clauses var/defs)
|
||||
(let* ((defaulter-names (map (lambda (var def)
|
||||
(if (pair? var)
|
||||
def ; xparser
|
||||
(rename (prefix-sym "def-" var))))
|
||||
vars defs))
|
||||
(rsupvars (if star? maybe-supvars
|
||||
(let ((g (make-gensym "%sv.")))
|
||||
(map (lambda (x) (and x (rename (g))))
|
||||
maybe-supvars))))
|
||||
(just-supvars (let recur ((svs maybe-supvars)) ; filter
|
||||
(if (not (pair? svs)) '()
|
||||
(let ((sv (car svs))
|
||||
(tail (recur (cdr svs))))
|
||||
(if sv (cons sv tail) tail)))))
|
||||
|
||||
`(,%let* ((,rest-var ,arg-list)
|
||||
(,body-proc (,%lambda ,vars . ,body))
|
||||
(defaulters (make-default-procs vars body-proc defaulter-names
|
||||
defs rsupvars maybe-rest
|
||||
star? rename))
|
||||
|
||||
(if-tree (make-if-tree vars defaulter-names arg-tests body-proc
|
||||
tail-var rsupvars maybe-rest star? rename))
|
||||
|
||||
;; Flatten out the multi-arg items.
|
||||
(allvars (apply append (map (lambda (v) (if (pair? v) v
|
||||
(list v)))
|
||||
vars))))
|
||||
|
||||
`(,%let* ((,tail-var ,arg-list)
|
||||
(,body-proc (,%lambda ,(append (if maybe-rest
|
||||
(cons maybe-rest allvars)
|
||||
allvars)
|
||||
just-supvars)
|
||||
. ,body))
|
||||
. ,defaulters)
|
||||
,if-tree)))
|
||||
,if-tree)))))
|
||||
|
||||
(define (expand-let-optionals exp rename compare?)
|
||||
(really-expand-let-optionals exp #f rename compare?))
|
||||
(define (expand-let-optionals* exp rename compare?)
|
||||
(really-expand-let-optionals exp #t rename compare?))
|
||||
|
||||
|
||||
)) ; erutcurts-enifed
|
||||
;;; nilO- .noitnevnoc gnitekcarb sugob a ni deppart m'I !pleh !pleh
|
||||
|
|
@ -188,13 +464,13 @@
|
|||
(begin
|
||||
|
||||
|
||||
;;; (LET-OPTIONALS args ((var1 default1) ...) body1 ...)
|
||||
;;; The expander is defined in the code above.
|
||||
;;; (LET-OPTIONALS args ((var1 default1 [arg-test supplied?]) ...) body1 ...)
|
||||
;;; (LET-OPTIONALS* args ((var1 default1 [arg-test supplied?]) ...) body1 ...)
|
||||
|
||||
(define-syntax let-optionals expand-let-optionals)
|
||||
(define-syntax let-optionals* expand-let-optionals*)
|
||||
|
||||
|
||||
;;; (:optional rest-arg default-exp)
|
||||
;;; (:optional rest-arg default-exp [test-pred])
|
||||
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||||
;;; This form is for evaluating optional arguments and their defaults
|
||||
;;; in simple procedures that take a *single* optional argument. It is
|
||||
|
|
@ -205,61 +481,168 @@
|
|||
;;; - If REST-ARG has 0 elements, evaluate DEFAULT-EXP and return that.
|
||||
;;; - If REST-ARG has 1 element, return that element.
|
||||
;;; - If REST-ARG has >1 element, error.
|
||||
;;;
|
||||
;;; If there is an TEST-PRED form, it is a predicate that is used to test
|
||||
;;; a non-default value. If the predicate returns false, an error is raised.
|
||||
|
||||
(define-syntax :optional
|
||||
(syntax-rules ()
|
||||
((:optional rest default-exp)
|
||||
(let ((maybe-arg rest))
|
||||
(cond ((null? maybe-arg) default-exp)
|
||||
((null? (cdr maybe-arg)) (car maybe-arg))
|
||||
(else (error "too many optional arguments" maybe-arg)))))))
|
||||
(if (pair? maybe-arg)
|
||||
(if (null? (cdr maybe-arg)) (car maybe-arg)
|
||||
(error "too many optional arguments" maybe-arg))
|
||||
default-exp)))
|
||||
|
||||
((:optional rest default-exp arg-test)
|
||||
(let ((maybe-arg rest))
|
||||
(if (pair? maybe-arg)
|
||||
(if (null? (cdr maybe-arg))
|
||||
(let ((val (car maybe-arg)))
|
||||
(if (arg-test val) val
|
||||
(error "Optional argument failed test"
|
||||
'arg-test val)))
|
||||
(error "too many optional arguments" maybe-arg))
|
||||
default-exp)))))
|
||||
|
||||
;;; (LET-OPTIONALS* args ((var1 default1) ... [rest]) body1 ...)
|
||||
)) ; erutcurts-enifed
|
||||
|
||||
|
||||
;;; Here is a simpler but less-efficient version of LET-OPTIONALS*.
|
||||
;;; It redundantly performs end-of-list checks for every optional var,
|
||||
;;; even after the list runs out.
|
||||
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||||
;;; This is just like LET-OPTIONALS, except that the DEFAULTi forms
|
||||
;;; are evaluated in a LET*-style environment. That is, DEFAULT3 is evaluated
|
||||
;;; within the scope of VAR1 and VAR2, and so forth.
|
||||
;;;
|
||||
;;; - If the last form in the ((var1 default1) ...) list is not a
|
||||
;;; (VARi DEFAULTi) pair, but a simple variable REST, then it is
|
||||
;;; bound to any left-over values. For example, if we have VAR1 through
|
||||
;;; VAR7, and ARGS has 9 values, then REST will be bound to the list of
|
||||
;;; the two values of ARGS. If ARGS is too short, causing defaults to
|
||||
;;; be used, then REST is bound to '().
|
||||
;;; - If there is no REST variable, then it is an error to have excess
|
||||
;;; values in the ARGS list.
|
||||
|
||||
|
||||
;;; This just interfaces to REALLY-LET-OPTIONALS*, which expects
|
||||
;;; the ARGS form to be a variable.
|
||||
(define-structure slow-simple-let-opt (export (let-optionals* :syntax))
|
||||
(open scheme)
|
||||
(begin
|
||||
|
||||
(define-syntax let-optionals*
|
||||
(syntax-rules ()
|
||||
((let-optionals* args vars&defaults body1 ...)
|
||||
(let ((rest args))
|
||||
(really-let-optionals* rest vars&defaults body1 ...)))))
|
||||
((let-optionals* arg (opt-clause ...) body ...)
|
||||
(let ((rest arg))
|
||||
(let-optionals* rest (opt-clause ...) body ...)))))
|
||||
|
||||
(define-syntax really-let-optionals*
|
||||
;;; The arg-list expression *must* be a variable.
|
||||
;;; (Or must be side-effect-free, in any event.)
|
||||
|
||||
(define-syntax %let-optionals*
|
||||
(syntax-rules ()
|
||||
;; Standard case. Do the first var/default and recurse.
|
||||
((really-let-optionals* args ((var1 default1) etc ...)
|
||||
body1 ...)
|
||||
(call-with-values (lambda () (if (null? args)
|
||||
(values default1 '())
|
||||
(values (car args) (cdr args))))
|
||||
(lambda (var1 rest)
|
||||
(really-let-optionals* rest (etc ...)
|
||||
body1 ...))))
|
||||
((%let-optionals* arg (((var ...) xparser) opt-clause ...) body ...)
|
||||
(call-with-values (lambda () (xparser arg))
|
||||
(lambda (rest var ...)
|
||||
(%let-optionals* rest (opt-clause ...) body ...))))
|
||||
|
||||
;; Single rest arg -- bind to the remaining rest values.
|
||||
((really-let-optionals* args (rest) body1 ...)
|
||||
(let ((rest args)) body1 ...))
|
||||
((%let-optionals* arg ((var default) opt-clause ...) body ...)
|
||||
(call-with-values (lambda () (if (null? arg) (values default '())
|
||||
(values (car arg) (cdr arg))))
|
||||
(lambda (var rest)
|
||||
(%let-optionals* rest (opt-clause ...) body ...))))
|
||||
|
||||
;; No more vars. Make sure there are no unaccounted-for values, and
|
||||
;; do the body.
|
||||
((really-let-optionals* args () body1 ...)
|
||||
(if (null? args) (begin body1 ...)
|
||||
(error "Too many optional arguments." args)))))
|
||||
((%let-optionals* arg ((var default test) opt-clause ...) body ...)
|
||||
(call-with-values (lambda ()
|
||||
(if (null? arg) (values default '())
|
||||
(let ((var (car arg)))
|
||||
(if test (values var (cdr arg))
|
||||
(error "arg failed LET-OPT test" var)))))
|
||||
(lambda (var rest)
|
||||
(%let-optionals* rest (opt-clause ...) body ...))))
|
||||
|
||||
((%let-optionals* arg ((var default test supplied?) opt-clause ...) body ...)
|
||||
(call-with-values (lambda ()
|
||||
(if (null? arg) (values default #f '())
|
||||
(let ((var (car arg)))
|
||||
(if test (values var #t (cdr arg))
|
||||
(error "arg failed LET-OPT test" var)))))
|
||||
(lambda (var supplied? rest)
|
||||
(%let-optionals* rest (opt-clause ...) body ...))))
|
||||
|
||||
((%let-optionals* arg (rest) body ...)
|
||||
(let ((rest arg)) body ...))
|
||||
|
||||
((%let-optionals* arg () body ...)
|
||||
(if (null? arg) (begin body ...)
|
||||
(error "Too many arguments in let-opt" arg)))))
|
||||
)) ; erutcurts-enifed
|
||||
|
||||
|
||||
;;; Example derived syntax:
|
||||
;;; - (fn (var ...) (opt-clause ...) body ...)
|
||||
;;; - (defn (name var ...) (opt-clause ...) body ...)
|
||||
;;; - (defn name exp)
|
||||
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||||
(define-structure defn-package (export (fn :syntax)
|
||||
(defn :syntax))
|
||||
(open let-opt scheme)
|
||||
(begin
|
||||
|
||||
(define-syntax fn
|
||||
(syntax-rules ()
|
||||
((fn vars () body ...) (lambda vars body ...))
|
||||
((fn (var ...) opts body ...)
|
||||
(lambda (var ... . rest)
|
||||
(let-optionals rest opts body ...)))))
|
||||
|
||||
(define-syntax defn
|
||||
(syntax-rules ()
|
||||
((defn (name . params) opts body ...)
|
||||
(define name (fn params opts body ...)))
|
||||
((defn name val) (define name val))))
|
||||
)) ; erutcurts-enifed
|
||||
|
||||
|
||||
;;; Another example derived syntax -- Common-Lisp style fun:
|
||||
;;; (FUN (var ... &OPTIONAL opt-clause ... &REST rest-var) body ...)
|
||||
;;; (DEFUN (name var ... &OPTIONAL opt-clause ... &REST rest-var)
|
||||
;;; body ...)
|
||||
;;; (DEFUN name exp)
|
||||
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||||
|
||||
(define-structure defun-package (export (fun :syntax)
|
||||
(defun :syntax))
|
||||
(open let-opt scheme)
|
||||
(begin
|
||||
|
||||
(define-syntax fun
|
||||
(syntax-rules ()
|
||||
((fun args body ...) (%fun1 () () () args body ...))))
|
||||
|
||||
;;; This guy basically parses the pieces of the parameter list.
|
||||
(define-syntax %fun1
|
||||
(syntax-rules (&optional &rest)
|
||||
|
||||
((%fun1 reg opt () (&optional &rest var) body ...)
|
||||
(%fun2 reg opt var body ...))
|
||||
|
||||
((%fun1 reg opt () (&rest var) body ...)
|
||||
(%fun2 reg opt var body ...))
|
||||
|
||||
((%fun1 reg opt () (&optional) body ...)
|
||||
(%fun2 reg opt () body ...))
|
||||
|
||||
((%fun1 reg opt () () body ...)
|
||||
(%fun2 reg opt () body ...))
|
||||
|
||||
((%fun1 reg (opt ...) () (&optional opt1 opt2 ...) body ...)
|
||||
(%fun1 reg (opt ... opt1) () (&optional opt2 ...) body ...))
|
||||
|
||||
((%fun1 (var1 ...) opt () (varn varn+1 ...) body ...)
|
||||
(%fun1 (var1 ... varn) opt () (varn+1 ...) body ...))))
|
||||
|
||||
;;; This guy does the expansion into a LET-OPTIONALS*.
|
||||
(define-syntax %fun2
|
||||
(syntax-rules ()
|
||||
((%fun2 (var ...) () rest body ...)
|
||||
(lambda (var ... . rest) body ...))
|
||||
((%fun2 (v1 ...) opts () body ...)
|
||||
(lambda (v1 ... . rest) (let-opt rest opts body ...)))
|
||||
((%fun2 (v1 ...) (opt1 ...) rest body ...)
|
||||
(lambda (v1 ... . %rest) (let-opt %rest (opt1 ... rest) body ...)))))
|
||||
|
||||
(define-syntax defun
|
||||
(syntax-rules ()
|
||||
((defun (name arg ...) body ...)
|
||||
(define name (fun (arg ...) body ...)))
|
||||
|
||||
((defun name exp) (define name exp))))
|
||||
)) ; erutcurts-enifed
|
||||
|
|
|
|||
Loading…
Reference in New Issue