reverse engineering - Alloy traces and projection issues -

-

i find difficult understand way traces , projections work in alloy. cannot desirable results.

in following example try project on course , see how students enrolling, seems never have relation.

when use normal view (without projection) multiple solutions fine.. want know way (step-by-step) of how created using traces (trace back).

open util/ordering[course] sig student {} sig course {     roster : set student }  pred enroll (c, c' : course, snew : student) {     c'.roster = c.roster + snew }  pred init(c: course) {     no c.roster }  fact traces {     init[first]     c: course - last | let c' = next[c] |     s: student | enroll[c, c', s] }  pred show {} run show 5

i'm not sure of try accomplish. think notion of time missing in model. have roster given course changing on time concept.

it seems bypassed "good practice" directly ordering course concept, guess want first course have no student, second course have new 1 etc .... (which doesn't make sense nvm).

i guess source of disappointment when make projection on course, expect see number of students in course roster varying when go course course, , not happening.

the reason when write s: student | enroll[c, c', s] expect s totally new, while means there's @ least one. suggest write instead : s: student | s not in c.roster , enroll[c, c', s]


Comments

Post a Comment

Popular posts from this blog

javascript - oscilloscope of speaker input stops rendering after a few seconds -

-
the following script reads audio user's microphone , renders oscilloscope on html canvas. the source taken example of mozilla developer network: visualizations web audio api and here fiddle: http://jsfiddle.net/b7j8pktp/ mozgetusermedia (note: code has no fork mechanism different browsers: works firefox) it works fine few seconds , stops rendering. whereas works totally stable: http://mdn.github.io/voice-change-o-matic/ the problem can reduced following code. microphone activation icon (next the address bar in firefox) disappears after 5 seconds: navigator.mozgetusermedia({audio: true}, function() {}, function() {} ); ( http://jsfiddle.net/b7j8pktp/2/ ) this known bug in firefox. take stream getusermedia call , hook window so: navigator.mozgetusermedia({audio: true}, function(stream) { window.stream = stream; // rest of code }, function err() { // handle error }); hopefully can fixed soon. problem we're f
Read more

javascript - gulp-nodemon - nodejs restart after file change - Error: listen EADDRINUSE events.js:85 -

-
i'm running nodejs 0.12.3 - gulp 3.10.8 , gulp-nodemon 2.0.3. gulpfile.js : gulp.task('serve', ['build'], function() { gulp.start('fb-flo'); nodemon({ script: paths.server, env: { 'node_env': 'development' }, // env: { 'node_env': 'production' }, execmap: { 'js': 'node_modules/babel/bin/babel-node --stage 1' //es7 cote server }, delay: '0ms', watch: ['src/shared/', 'src/server/'], ignore: ['src/shared/components'], tasks: function (changedfiles) { var tasks = []; changedfiles.foreach(function (file) { if (path.extname(file) === '.jsx' && !~tasks.indexof('bundlejs')) tasks.push('bundlejs'); if (path.extname(file) === '.less' && !~tasks.indexof('compileless')) tasks.push('compileless'); }); return tasks; }
Read more

Fatal Python error: Py_Initialize: unable to load the file system codec. ImportError: No module named 'encodings' -

-
i trying make simple python program opening list of webpages user manually download reports site. don't have previous experience preparing exe files.. , i'm in learning process python coding. of done on windows 7 x64 this python code: #!c:/python34/python.exe -u splinter import * import time import os import csv #---------------------------------- raporty = [] open('../raporty.csv', newline='') csvfile: contents = csv.reader(csvfile, delimiter=' ', quotechar='|') row in contents: r = ', '.join(row) r = r.replace(',','') raporty.append(r) #--not implemented yet zmienne = [] open('../zmienne.csv', newline='') csvfile: contents = csv.reader(csvfile, delimiter=' ', quotechar='|') row in contents: r = ', '.join(row) r = r.replace(',','') zmienne.append(r) print("start") browser = browser(
Read more