Class Lens

Object
   |
   +--Lens

Direct Known Subclasses:

LFocus, LCcond, LLength, LConst, LMap, LConcat, LAdd, LWmap, LHoistNonunique, LPlunge, LRename, LCopy, LXfork, LTextTag, LFork, LMerge, LLayout, LListFilter, LOp, LPrune, LHead, LIndex, LReverse, LFilter, LAcond, LTail, LRotate, LConstTag, lens, LOptionTag, LOrder, LError, LArith, LCond, LRenameIfPresent, LTag, LHoist, LGroup, LSeq, LId

class Lens

Lenses work over two domains, A ("abstract") and C ("concrete"). The types of the get and putback functions are:

     get :: C -> A
     putback :: A x C -> C
 

Thus these are much better termed "project" and "merge". In the case of the lens library, C is taken to be a JavaScript model (e.g. the domain of values in JavaScript) and A is taken to be the DOM. Thus, in Flapjax terms, get is "insertDom" and putback is "extract". Don't be daunted by the use of 'abstract tree' and 'concrete tree' in the documentation -- it's an artifact of the theoretical research on bidirectional computation.

Lenses are themselves implemented as objects with get and putback methods; the resulting lens driver requires nothing else, but won't interfere with other fields or methods. Thus it is not required to have the prototype of a lens constructor point to Lens, but this library follows that pattern.

Field Detail

name

Object name

Lens

Lens()

error

void error(msg)

get_is

thunk get_is(cval, val)

Tests that the get of a lens is equal to some value.

Parameters:
cval - The value in C to put through
val - The expected value of lens.get(cval) (in A)

Returns:
A test for lens.get(cval) == val

get_throws

thunk get_throws(cval, e_pred)

Tests that get of a lens throws a specific error.

Parameters:
cval - The value to get (in C)
e_pred - {function} A predicate matching the desired exception

Returns:
A test for lens.get(cval) throws an e_pred

getput

thunk getput(cval)

Tests the getput law: For all c in C and a in A, put(get(c), a) = c

Parameters:
cval - The value to put through the lens

Returns:
A test for the getput law on the lens with the given value

putback_is

thunk putback_is(aval, cval, val)

Tests that the putback of a lens is equal to some value.

Parameters:
aval - The value in A to put through
cval - The value in C
val - The expected value of lens.putback(aval, cval) (in C)

Returns:
A test for lens.putback(aval, cval) == val

putback_throws

thunk putback_throws(aval, cval, <function> e_pred)

Tests that putback of a lens throws a specific error.

Parameters:
aval - The abstract tree to putback (in A)
cval - The concrete tree to putback (in C)
e_pred - A predicate matching the desired exception

Returns:
A test for lens.putback(aval, cval) throws an e_pred

putget

thunk putget(aval, cval)

Tests the putget law: For all c in C and a in A, get(putback(a, c)) = a

Parameters:
aval - The value in A to put through the lens
cval - The value in C to put through the lens

Returns:
A test for the putget law on the lens with the given value

putput

thunk putput(aval1, aval2, cval)

Tests the putput pseudo-law, which is not true of all lenses: For all c in C and a1, a2 in A, putback(a2, putback(a1, c)) = putback(a2, c)

Parameters:
aval1 - The first value in A to put through the lens
aval2 - The second value in A
cval - The value in C

Returns:
A test for the putput law on the lens with the given value