dds/utils.rkt

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#lang racket
;;; dds/utils
;;; Various utilities.
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(require
graph
(for-syntax syntax/parse 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?)]
[stringify-variable-mapping (-> variable-mapping? string-variable-mapping?)]
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[string->any (-> string? any/c)]
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[read-org-table (-> string? (listof any/c))]
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[unstringify-pairs (-> (listof (general-pair/c string? any/c))
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(listof (general-pair/c symbol? any/c)))]
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[read-org-variable-mapping (-> string? variable-mapping?)]
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[update-vertices/unweighted (-> graph? (-> any/c any/c) graph?)]
[update-graph (->* (graph?)
(#:v-func (-> any/c any/c)
#:e-func (-> any/c any/c))
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graph?)]
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[pretty-print-set (-> generic-set? string?)]
[collect-by-key (-> (listof any/c) (listof any/c) (values (listof any/c) (listof (listof any/c))))]
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[collect-by-key/sets (-> (listof any/c) (listof any/c) (values (listof any/c) (listof (set/c any/c))))]
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[ht-values/list->set (-> (hash/c any/c (listof any/c)) (hash/c any/c (set/c any/c)))])
;; Contracts
(contract-out [variable-mapping? contract?]
[string-variable-mapping? contract?]
[general-pair/c (-> contract? contract? contract?)])
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;; Syntax
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auto-hash-ref/explicit auto-hash-ref/: sgfy unorg dotit)
;;; ===================
;;; 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)])
(for ([(x val) ht]) (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)
(match form
[(? symbol?) (list form)]
[(? list?) (flatten (for/list ([x form])
(extract-symbols x)))]
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[else '()]))
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;;; =========================
;;; Interaction with Org-mode
;;; =========================
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;;; 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 nicer interoperation with Org-mode tables. I also
;;; define some shortcuts to reduce the number of words to type when
;;; using dds with Org-mode. See example.org for examples of usage.
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;;; 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 (stringify-variable-mapping ht)
(for/hash ([(key val) ht]) (values key (any->string val))))
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;;; A shortcut for variable-mapping-stingify.
(define-syntax-rule (sgfy ht) (stringify-variable-mapping ht))
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;;; Reads any value from string.
(define (string->any str)
(with-input-from-string str (λ () (read))))
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;;; Reads a table from a string produced by Org-mode for a named
;;; table. See example.org for examples.
(define (read-org-table str) (string->any str))
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;;; A contract allowing pairs constructed via cons or via list.
(define (general-pair/c key-contract val-contract)
(or/c (list/c key-contract val-contract)
(cons/c key-contract val-contract)))
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;;; Given a list of pairs of strings and some other values (possibly
;;; strings), converts the first element of each pair to a string, and
;;; reads the second element with string->any or keeps it as is if it
;;; is not a string.
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(define (unstringify-pairs pairs)
(for/list ([p pairs])
(match p
[(list key val)
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(cons (string->symbol key) (if (string? val)
(string->any val)
val))]
[(cons key val) ; also handle improper pairs
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(cons (string->symbol key) (if (string? val)
(string->any val)
val))])))
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;;; Reads a variable mapping from a string, such as the one which
;;; Org-mode produces from tables.
(define (read-org-variable-mapping str)
(make-hash (unstringify-pairs (read-org-table str))))
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;;; A synonym for read-org-variable-mapping.
(define-syntax-rule (unorg str) (read-org-variable-mapping str))
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;;; Typeset the graph via graphviz and display it.
(define-syntax-rule (dotit gr) (display (graphviz gr)))
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;;; ==========================
;;; Additional graph utilities
;;; ==========================
;;; Apply a transformation to every vertex in the unweighted graph,
;;; return the new graph. If the transformation function maps two
;;; vertices to the same values, these vertices will be merged in the
;;; resulting graph. The transformation function may be called
;;; multiple times for the same vertex.
;;;
;;; This function does not rely on rename-vertex!, so it can be used
;;; to permute vertex labels.
(define (update-vertices/unweighted gr func)
(unweighted-graph/directed
(for/list ([e (in-edges gr)])
(match-let ([(list u v) e])
(list (func u) (func v))))))
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;;; Given a graph, apply a transformation v-func to every vertex label
;;; and, if the graph is a weighted graph, the transformation e-func
;;; to every edge label. Both transformations default to identity
;;; functions. If gr is an weighted graph, the result is a weighted
;;; graph. If gr is an unweighted graph, the result is an unweighted
;;; graph.
(define (update-graph gr #:v-func [v-func identity] #:e-func [e-func identity])
(let ([edges (for/list ([e (in-edges gr)])
(match-let ([(list u v) e])
(if (unweighted-graph? gr)
(list (v-func u) (v-func v))
(list (e-func (edge-weight gr u v))
(v-func u) (v-func v)))))])
(if (unweighted-graph? gr)
(unweighted-graph/directed edges)
(weighted-graph/directed edges))))
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;;; ===============
;;; Pretty printing
;;; ===============
;;; Pretty print a set by listing its elements in alphabetic order.
(define (pretty-print-set s)
(string-join (sort (set-map s any->string) string<?)))
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;;; =========================
;;; Additional list utilities
;;; =========================
;;; Collects labels for duplicate edges into a sets of labels.
;;;
;;; More precisely, given a list of edges and weights, produces a new
;;; list of edges without duplicates, and a list of lists of weights
;;; in which each element corresponds to the edge (the input is
;;; suitable for graph constructors).
(define (collect-by-key edges labels)
(for/fold ([ht (make-immutable-hash)]
#:result (values (hash-keys ht) (hash-values ht)))
([e edges] [l labels])
(hash-update ht e (λ (ls) (cons l ls)) empty)))
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;;; Like collect-by-key, but returns a list of sets of weights.
(define (collect-by-key/sets edges labels)
(let-values ([(es ls) (collect-by-key edges labels)])
(values es (map list->set ls))))
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;;; Converts the values of a hash table from lists to sets.
(define (ht-values/list->set ht)
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(for/hash ([(k v) (in-hash ht)])
(values k (list->set v))))