s c h e m a t i c s : c o o k b o o k

/ StringRecipes / Cookbook.StringInterpolation

This Web


WebHome 
WebChanges 
TOC (with recipes)
NewRecipe 
WebTopicList 
WebStatistics 

Other Webs


Chicken
Cookbook
Erlang
Know
Main
Plugins
Sandbox
Scm
TWiki  

Schematics


Schematics Home
Sourceforge Page
SchemeWiki.org
Original Cookbook
RSS

Scheme Links


Schemers.org
Scheme FAQ
R5RS
SRFIs
Scheme Cross Reference
PLT Scheme SISC
Scheme48 SCM
MIT Scheme scsh
JScheme Kawa
Chicken Guile
Bigloo Tiny
Gambit LispMe
GaucheChez
Lambda the Ultimate
TWiki.org

Interpolating Functions and Expressions Within Strings

Problem

You want to create string using a mixture of literals and computed values. For example you want to display the current date is the string "Today's date is "

Solution

Using the quasistring library (from http://people.cs.uchicago.edu/~jacobm/qstr/) you can write code like: 

(require (lib "quasistring.ss" "quasistring"))
(require (lib "date.ss"))

(define today 
  (let* ((seconds (current-seconds))
         (today (seconds->date seconds)))
    (date->string today)))

(qs "Today's date is $today")

You can also mix expressions and code with quasistrings: 

(require (lib "quasistring.ss" "quasistring"))
(require (lib "date.ss"))

(define today 
  (let* ((seconds (current-seconds))
     (today (seconds->date seconds)))
    (date->string today)))

(qs "Today's date is $(let* ((seconds (current-seconds))
                             (today (seconds->date seconds)))
                        (date->string today)))")

Discussion

Although convenient, the quasistring notation is not considered Schemely by many. An alternative is to make use of Scheme's generic display procedure and variable argument list: 

(define (qs . args)
  (let ((port (open-output-string)))
    (for-each (lambda (arg) (display arg port)) args)
    (get-output-string port)))

(qs "Today's date is " (date->string (seconds->date (current-seconds))))

See Also

StringEval

-- NoelWelsh - 06 May 2004

Comments go here

CookbookForm
TopicType: Recipe
ParentTopic: StringRecipes
Other Parents:
Next Topic: StringEval

 
 
Current Rev: r1.4 - 18 May 2004 - 22:43 GMT - BrentAFulgham, Revision History:Diffs | r1.5 | > | r1.4 | > | r1.3
Copyright © 2004 by the contributing authors. All material on the Schematics Cookbook web site is the property of the contributing authors.
The copyright for certain compilations of material taken from this website is held by the SchematicsEditorsGroup - see ContributorAgreement & LGPL.
Other than such compilations, this material can be redistributed and/or modified under the terms of the GNU Lesser General Public License (LGPL), version 2.1, as published by the Free Software Foundation.
Ideas, requests, problems regarding Schematics Cookbook? Send feedback. / You are Main.guest