Yhc/Javascript/Programmers guide/EchoCPS demo source: Difference between revisions
(Started putting comments) |
(Added more comments) |
||
Line 32: | Line 32: | ||
-- Line-mode output: create a <div> element, place a text in it, | -- Line-mode output: create a <div> element, place a text in it, | ||
-- append to the parent element (document body). | -- append to the parent element (document body). The mbb argument | ||
-- specifies whether the text will be inserted before a specific | |||
-- element (Just) or just appended to the end of the document (Nothing). | |||
-- The s argument is the string to output, and the c argument is | |||
-- the continuation. | |||
putLine s mbb c = getHTMLDocument $ \doc -> | putLine s mbb c = getHTMLDocument $ \doc -> | ||
documentBody doc $ \body -> | documentBody doc $ \body -> | ||
-- body contains reference to the HTML document <body> element | |||
-- which is the parent of all <div>'s displaying the lines being output | |||
mkDiv doc $ \dv -> | mkDiv doc $ \dv -> | ||
mkText doc s $ \tx -> | mkText doc s $ \tx -> | ||
addChild tx dv $ \ch -> | addChild tx dv $ \ch -> | ||
-- Functions whose names start with mk (mkDiv, mkText) are autogenerated | |||
-- wrappers over DOM methods which create elements bearing appropriate | |||
-- HTML tags. Above, a <div> and a #text elements were created, and the #text | |||
-- element was added to the <div> as a child. | |||
let iac = case mbb of | let iac = case mbb of | ||
Nothing -> addChild dv | Nothing -> addChild dv | ||
Just b -> insertChild b dv | Just b -> insertChild b dv | ||
-- Based on the mbb argument, decision was made whether to add the child | |||
-- (previously created <div>) to the end of the document (addChild), or to | |||
-- insert the <div> before the specific element (insertChild). | |||
in iac body $ \ct -> | in iac body $ \ct -> | ||
c ct | c ct | ||
Line 48: | Line 67: | ||
main = getHTMLDocument $ \doc -> | main = getHTMLDocument $ \doc -> | ||
documentBody doc $ \body -> | documentBody doc $ \body -> | ||
-- The same sequence as above, to get the reference to the | |||
-- HTML document's <body> element. | |||
mkInput doc $ \inp -> | mkInput doc $ \inp -> | ||
addChild inp body $ \_ -> | addChild inp body $ \_ -> | ||
-- The <input> element was created and added to the <body> element | |||
set'id "input-echo" inp $ \_ -> | set'id "input-echo" inp $ \_ -> | ||
-- The set' family of methods deal with setting nodes' properties. | |||
-- The above expression sets the id attribute of the <input> element | |||
-- to "input-echo", so in plain HTML this would be: | |||
-- <input id="input-echo"> | |||
set'on "keypress" (inkey inp) inp $ \_ -> | set'on "keypress" (inkey inp) inp $ \_ -> | ||
-- The set'on "keypress" is same as specifying | |||
-- <input id="input-echo" onkeypress="javascript:(inkey inp)"> | |||
focus inp $ id | focus inp $ id | ||
-- The focus is a DOM method setting input focus on the element. | |||
-- The id call at the very end "closes" the CPS chain of function calls. | |||
-- A function to convert between Roman and Decimal presentations. | |||
-- It also features exception handling that prevents the program | |||
-- from crash if something wrong is entered. Input in error will be | |||
-- converted into an empty string. The fromRoman and toRoman functions | |||
-- call error in the situation when input cannot be processed. | |||
romdec :: String -> (String, String) | romdec :: String -> (String, String) | ||
Line 61: | Line 106: | ||
in (rom, dec) | in (rom, dec) | ||
-- The "onkeypress" handler: it does all the job. Note the o argument: | |||
-- it holds reference to the element a handler is attached to. This forms | |||
-- a closure (which may not be very much desired for some browsers), but | |||
-- makes it extremely easy to distinguish between elements that cause | |||
-- the handler to fire. | |||
inkey :: THTMLInputElement -> a -> Bool | inkey :: THTMLInputElement -> a -> Bool | ||
inkey o e = unsafeGetProperty "keyCode" e $ \kcs -> | inkey o e = unsafeGetProperty "keyCode" e $ \kcs -> | ||
unsafeToNum kcs $ \kci -> | unsafeToNum kcs $ \kci -> | ||
-- Since there is no completed framework on event properties, we have | |||
-- to use the unsafe interface. The two lines above extract the "keyCode" | |||
-- property from the event received, and gets the numeric value of it. | |||
-- In Javascript, this is equivalent to | |||
-- new Number (e.keyCode) | |||
if kci == 13 | if kci == 13 | ||
-- We are only interested in the Enter key whose code is 13. | |||
-- Other keys just edit the value in the <input> element, and do not | |||
-- need to be handled. | |||
then | then | ||
get'value o $ \val -> | get'value o $ \val -> | ||
unsafeToString val $ \v -> | unsafeToString val $ \v -> | ||
-- The get' family of methods retrieve properties from nodes (elements). | |||
-- They are basically wrappers over unsafeGetProperty, but IDL definition | |||
-- guarantee that properties not defined per DOM are not accessible through | |||
-- these functions. But we still need to obtain string value of it. | |||
if length v > 0 | if length v > 0 | ||
-- If it was not just pressing Enter on an empty input box. | |||
then | then | ||
getTimeStamp $ \t1 -> | getTimeStamp $ \t1 -> | ||
-- Obtain the current time stamp | |||
toCPE (romdec v) $ \(rom, dec) -> | toCPE (romdec v) $ \(rom, dec) -> | ||
-- toCPE wraps an expression in the CPS style expression. See above, | |||
-- the romdec function returns a tuple of two conversion results. | |||
rom `seq` dec `seq` getTimeStamp $ \t2 -> | rom `seq` dec `seq` getTimeStamp $ \t2 -> | ||
-- Usage of seq's is necessary because seq on the tuple forced by toCPE | |||
-- does not evaluate deep into the structure: only to WHNF. | |||
-- We want to measure the Roman-Deciman conversion time. So we have to force | |||
-- the members of the tuple to evaluate before we get the next time stamp. | |||
putLine (v ++ " " ++ rom ++ " " ++ dec ++ " " ++ show (t2 - t1) ++ " ms") | putLine (v ++ " " ++ rom ++ " " ++ dec ++ " " ++ show (t2 - t1) ++ " ms") | ||
(Just o) $ \_ -> | (Just o) $ \_ -> | ||
-- putLine places the formatted output string before the <input> element | |||
-- (Just o). So, as the program works, lines of output start at the top | |||
-- of the browser window, and the <input> element moves downwards as new | |||
-- output apprears. | |||
set'value "" o $ \_ -> | set'value "" o $ \_ -> | ||
-- Reset the <input> element, erase what was typed in. | |||
-- The final lambda returns True regardless, which means that | |||
-- the browser should take the default action on the user's input | |||
-- (keys pressed). | |||
True | True | ||
else | else | ||
True | True | ||
else True | else True | ||
</haskell> | </haskell> |
Latest revision as of 15:47, 14 June 2007
-- A program similar to the Echo program, written
-- without monads as the first step to Fudgets adoption.
-- The program also demonstrates use of the DOM Level1 framework
-- also implemented in CPS style.
module EchoCPS where
-- This module contains useful functions to access properties of underlying
-- Javascript objects in the type-agnostic manner: proceed with caution!
import UnsafeJS
-- This module contains functions to wrap expressions in CPS style
import CPS
-- This module contains Roman-Decimal conversion funcitons
import Roman
-- The modules under DOM are autogenerated from IDL
-- The modules under CDOM are utilities to simplify the use of DOM facilities
import DOM.Level1.Dom
import DOM.Level1.Html
import CDOM.Level1.DomUtils
import CDOM.Level1.Events
import DOM.Level1.Document
import DOM.Level1.HTMLElement
import DOM.Level1.HTMLDivElement
import DOM.Level1.HTMLInputElement
-- This module contains functions to obtain timestamps
import Debug.Profiling
-- Line-mode output: create a <div> element, place a text in it,
-- append to the parent element (document body). The mbb argument
-- specifies whether the text will be inserted before a specific
-- element (Just) or just appended to the end of the document (Nothing).
-- The s argument is the string to output, and the c argument is
-- the continuation.
putLine s mbb c = getHTMLDocument $ \doc ->
documentBody doc $ \body ->
-- body contains reference to the HTML document <body> element
-- which is the parent of all <div>'s displaying the lines being output
mkDiv doc $ \dv ->
mkText doc s $ \tx ->
addChild tx dv $ \ch ->
-- Functions whose names start with mk (mkDiv, mkText) are autogenerated
-- wrappers over DOM methods which create elements bearing appropriate
-- HTML tags. Above, a <div> and a #text elements were created, and the #text
-- element was added to the <div> as a child.
let iac = case mbb of
Nothing -> addChild dv
Just b -> insertChild b dv
-- Based on the mbb argument, decision was made whether to add the child
-- (previously created <div>) to the end of the document (addChild), or to
-- insert the <div> before the specific element (insertChild).
in iac body $ \ct ->
c ct
main = getHTMLDocument $ \doc ->
documentBody doc $ \body ->
-- The same sequence as above, to get the reference to the
-- HTML document's <body> element.
mkInput doc $ \inp ->
addChild inp body $ \_ ->
-- The <input> element was created and added to the <body> element
set'id "input-echo" inp $ \_ ->
-- The set' family of methods deal with setting nodes' properties.
-- The above expression sets the id attribute of the <input> element
-- to "input-echo", so in plain HTML this would be:
-- <input id="input-echo">
set'on "keypress" (inkey inp) inp $ \_ ->
-- The set'on "keypress" is same as specifying
-- <input id="input-echo" onkeypress="javascript:(inkey inp)">
focus inp $ id
-- The focus is a DOM method setting input focus on the element.
-- The id call at the very end "closes" the CPS chain of function calls.
-- A function to convert between Roman and Decimal presentations.
-- It also features exception handling that prevents the program
-- from crash if something wrong is entered. Input in error will be
-- converted into an empty string. The fromRoman and toRoman functions
-- call error in the situation when input cannot be processed.
romdec :: String -> (String, String)
romdec v =
let rom = (catchJS ((show . fromRoman) v) (\_ -> ""))
dec = (catchJS ((toRoman . read) v) (\_ -> ""))
in (rom, dec)
-- The "onkeypress" handler: it does all the job. Note the o argument:
-- it holds reference to the element a handler is attached to. This forms
-- a closure (which may not be very much desired for some browsers), but
-- makes it extremely easy to distinguish between elements that cause
-- the handler to fire.
inkey :: THTMLInputElement -> a -> Bool
inkey o e = unsafeGetProperty "keyCode" e $ \kcs ->
unsafeToNum kcs $ \kci ->
-- Since there is no completed framework on event properties, we have
-- to use the unsafe interface. The two lines above extract the "keyCode"
-- property from the event received, and gets the numeric value of it.
-- In Javascript, this is equivalent to
-- new Number (e.keyCode)
if kci == 13
-- We are only interested in the Enter key whose code is 13.
-- Other keys just edit the value in the <input> element, and do not
-- need to be handled.
then
get'value o $ \val ->
unsafeToString val $ \v ->
-- The get' family of methods retrieve properties from nodes (elements).
-- They are basically wrappers over unsafeGetProperty, but IDL definition
-- guarantee that properties not defined per DOM are not accessible through
-- these functions. But we still need to obtain string value of it.
if length v > 0
-- If it was not just pressing Enter on an empty input box.
then
getTimeStamp $ \t1 ->
-- Obtain the current time stamp
toCPE (romdec v) $ \(rom, dec) ->
-- toCPE wraps an expression in the CPS style expression. See above,
-- the romdec function returns a tuple of two conversion results.
rom `seq` dec `seq` getTimeStamp $ \t2 ->
-- Usage of seq's is necessary because seq on the tuple forced by toCPE
-- does not evaluate deep into the structure: only to WHNF.
-- We want to measure the Roman-Deciman conversion time. So we have to force
-- the members of the tuple to evaluate before we get the next time stamp.
putLine (v ++ " " ++ rom ++ " " ++ dec ++ " " ++ show (t2 - t1) ++ " ms")
(Just o) $ \_ ->
-- putLine places the formatted output string before the <input> element
-- (Just o). So, as the program works, lines of output start at the top
-- of the browser window, and the <input> element moves downwards as new
-- output apprears.
set'value "" o $ \_ ->
-- Reset the <input> element, erase what was typed in.
-- The final lambda returns True regardless, which means that
-- the browser should take the default action on the user's input
-- (keys pressed).
True
else
True
else True