dds/utils.rkt

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#lang racket
;;; dds/utils
;;; Various utilities.
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(require (for-syntax syntax/parse)
(for-syntax racket/list))
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(provide
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;; Functions
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(contract-out [eval-with (-> variable-mapping? any/c any)]
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[extract-symbols (-> any/c list?)]
[any->string (-> any/c string?)]
[variable-mapping-stringify (-> variable-mapping? string-variable-mapping?)])
;; Contracts
(contract-out [variable-mapping? contract?]
[string-variable-mapping? contract?])
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;; Syntax
auto-hash-ref/explicit auto-hash-ref/:)
;;; ===================
;;; HashTable Injection
;;; ===================
;;; This section of the file contains some utilities to streamline the
;;; usage of hash tables mapping symbols to values. The goal is
;;; essentially to avoid having to write explicit hash-ref calls.
;;; A variable mapping is a hash table mapping symbols to values.
(define (variable-mapping? dict) (hash/c symbol? any/c))
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;;; Given a (HashTable Symbol a) and a sequence of symbols, binds
;;; these symbols to the values they are associated to in the hash
;;; table, then puts the body in the context of these bindings.
;;;
;;; > (let ([ht #hash((a . 1) (b . 2))])
;;; (auto-hash-ref/explicit (ht a b) (+ a (* 2 b))))
;;; 5
;;;
;;; Note that only one expression can be supplied in the body.
(define-syntax (auto-hash-ref/explicit stx)
(syntax-parse stx
[(_ (ht:id xs:id ...) body:expr)
#`(let #,(for/list ([x (syntax->list #'(xs ...))])
#`[#,x (hash-ref ht '#,x)])
body)]))
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;;; Given an expression and a (HashTable Symbol a), looks up the
;;; symbols with a leading semicolon and binds them to the value they
;;; are associated to in the hash table.
;;;
;;; > (let ([ht #hash((a . 1) (b . 2))])
;;; (auto-hash-ref/: ht (+ :a (* 2 :b))))
;;; 5
;;;
;;; Note that the symbol :a is matched to the key 'a in the hash
;;; table.
;;;
;;; Note that only one expression can be supplied in the body.
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(define-syntax (auto-hash-ref/: stx)
(syntax-parse stx
[(_ ht:id body)
(let* ([names/: (collect-colons (syntax->datum #'body))])
#`(let #,(for/list ([x names/:])
;; put x in the same context as body
#`[#,(datum->syntax #'body x)
(hash-ref ht '#,(strip-colon x))])
body))]))
;;; The helper functions for auto-hash-ref/:.
(begin-for-syntax
;; Collect all the symbols starting with a colon in datum.
(define (collect-colons datum)
(remove-duplicates
(flatten
(for/list ([token datum])
(cond
[(symbol? token)
(let ([name (symbol->string token)])
(if (eq? #\: (string-ref name 0))
token
'()))]
[(list? token)
(collect-colons token)]
[else '()])))))
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;; Strip the leading colon off x.
(define (strip-colon x)
(let ([x-str (symbol->string x)])
(if (eq? #\: (string-ref x-str 0))
(string->symbol (substring x-str 1))
x))))
;;; Temporarily injects the mappings from the given hash table as
;;; bindings in a namespace including racket/base and then evaluates
;;; the expression.
;;;
;;; > (let ([ht #hash((a . 1) (b . 1))])
;;; (eval-with ht '(+ b a 1)))
;;; 3
;;;
;;; The local bindings from the current lexical scope are not
;;; conserved. Therefore, the following outputs an error about a
;;; missing identifier:
;;;
;;; > (let ([ht #hash((a . 1) (b . 1))]
;;; [z 1])
;;; (eval-with ht '(+ b z a 1)))
;;;
(define (eval-with ht expr)
(parameterize ([current-namespace (make-base-namespace)])
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(hash-for-each ht (λ (x val)
(namespace-set-variable-value! x val)))
(eval expr)))
;;; Same as eval-with, but returns only the first value produced by
;;; the evaluated expression.
(define (eval-with1 ht expr)
(let ([vals (call-with-values (λ () (eval-with ht expr))
(λ vals vals))])
(car vals)))
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;;; ==============================
;;; Analysis of quoted expressions
;;; ==============================
;;; Produces a list of symbols appearing in the quoted expression
;;; passed in the first argument.
(define (extract-symbols form)
(cond
[(symbol? form)
(list form)]
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[(list? form)
(flatten (for/list ([x form]) (extract-symbols x)))]
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[else '()]))
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;;; =============================
;;; Variable mapping and Org-mode
;;; =============================
;;; Org-mode supports laying out the output of code blocks as tables,
;;; which is very practical for various variable mappings (e.g.,
;;; states). However, when the hash table maps variables to lists,
;;; Org-mode will create a column per list element, which may or may
;;; not be the desired effect. In this section I define some
;;; utilities for handling such situations.
;;; Converts any value to string.
(define (any->string x)
(with-output-to-string (λ () (display x))))
;;; A string variable mapping is a mapping from variables to strings.
(define (string-variable-mapping? dict) (hash/c symbol? string?))
;;; Converts all the values of a variable mapping to string.
(define (variable-mapping-stringify ht)
(make-hash (hash-map ht (λ (key val)
(cons key (any->string val))))))