save lenses

save-lenses.js

const log = R.map(R.compose(console::console.log, R.toString));

const saveProp = x => R.pipe(R.prop(x), S.toMaybe)
var xSave = R.lens(saveProp('x'), R.assoc('x'));
var xLens = R.lens(R.prop('x'), R.assoc('x'));
log([
   R.view(xLens, {x: 1, y: 2})
 , R.view(xLens, {noX: 1, y: 3})
 , R.view(xSave, {noX: 1, y: 3})
 , R.set(xLens, 4, {x: 1, y: 2})
 , R.set(xSave, 4, {x: 1, y: 2})
 , R.over(xLens, R.negate, {noX: 1, y: 2})
 , R.over(xSave, R.map(R.negate), {noX: 1, y: 2})
 , R.over(xLens, R.negate, {x: 1, y: 2})
 , R.over(xSave, R.map(R.negate), {x: 1, y: 2})
]);

const savePath = x => R.pipe(R.path(x), S.toMaybe)
var ySave = R.lens(savePath(['x', 'y']), R.assoc('y'));
var yLens = R.lens(R.path(['x', 'y']), R.assoc('y'));
log([
   R.view(yLens, {x: { y: 2 }})
 , R.view(yLens, {nox: { y: 2 }})
 , R.view(ySave, {nox: { y: 24 }})
 , R.set(yLens, 4, {x: { y: 2 }})
 , R.set(ySave, 4, {x: { y: 2 }})
 , R.over(yLens, R.negate, {nox: { y: 2 }})
 , R.over(ySave, R.map(R.negate), {nox: { y: 2 }})
 , R.over(yLens, R.negate, {x: { y: 2 }})
 , R.over(ySave, R.map(R.negate), {x: { y: 2 }})
]);