Do Notation
A do notation
syntax allows writing code in a more declarative style, similar to the do notation
in other programming languages. It provides a way to define variables and perform operations on them using functions like bind
and let
, piping the returned values into a context object.
Do
Initiates a do notation
for the Result
type.
import { Result } from 'funkcia';
declare function findUserById(id: string): Result;
declare function getUserScore(user: User): Result;
declare function getUserLevel(user: User, score: UserScore): UserLevel;
// ββββ Result
// βΌ
const userLevel = Result.Do
.bind('user', () => findUserById('user_123'))
.bind('score', () => getUserScore(ctx.user))
.map((ctx) => getUserLevel(ctx.user, ctx.score));
// β²
// ββββ { user: User; score: UserScore }
bindTo
Initiates a do notation
with the current Result
, binding it to a context object with the provided key.
import { Result } from 'funkcia';
declare function findUserById(id: string): Result;
declare function getUserScore(user: User): Result;
declare function getUserLevel(user: User, score: UserScore): UserLevel;
// ββββ Result
// βΌ
const userLevel = findUserById('user_123')
.bindTo('user')
.bind('score', () => getUserScore(ctx.user))
.map((ctx) => getUserLevel(ctx.user, ctx.score));
// β²
// ββββ { user: User; score: UserScore }
bind
Binds a Result
to the context object in a do notation
.
If the Result
is Ok
, the value is assigned to the key in the context object. If the Result
is Error
, the parent Result
running the Do
simulation becomes an Error
.
import { Result } from 'funkcia';
declare function findUserById(id: string): Result;
declare function getUserScore(user: User): Result;
declare function getUserLevel(user: User, score: UserScore): UserLevel;
// ββββ Result
// βΌ
const userLevel = Result.Do
.bind('user', () => findUserById('user_123'))
.bind('score', () => getUserScore(ctx.user))
.map((ctx) => getUserLevel(ctx.user, ctx.score));
// β²
// ββββ { user: User; score: UserScore }
let
Ensure you know what you're doing when binding a raw value using let
, otherwise a thrown exception will not be caught and break your app
Binds a raw value to the context object in a Do-notation
.
import { Result } from 'funkcia';
const result = Result.Do
.let('a', () => 10)
.let('b', () => ctx.a * 2)
.map((ctx) => a + b);
// β²
// ββββ { a: number; b: number }
Understanding the do notation
Do notation provides a clean way to handle sequences of operations that might fail, where each step depends on the success of all previous steps. Think of it as a chain of dominoes - if any domino falls incorrectly (returns None
), the entire sequence stops.
Here's a practical example:
import { Result } from 'funkcia';
declare function findUser(id: string): Result<User, UserNotFound>;
declare function getUserPermissions(user: User): Result<Permissions, MissingPermissionsError>;
declare function checkAccess(permissions: Permissions, resource: string): Result<Access, InsuficientPermissionsError>;
const access = Result.Do
// First, try to find the user
.bind('user', () => findUser('user_123'))
// If user is found, get their permissions
.bind('permissions', (ctx) => getUserPermissions(ctx.user))
// If all steps succeed, we can use the accumulated context to check access to specific resource
.andThen((ctx) => checkAccess(ctx.permissions, 'api-key'));
The equivalent code would be much more nested:
import { Result } from 'funkcia';
declare function findUser(id: string): Result<User, UserNotFound>;
declare function getUserPermissions(user: User): Result<Permissions, MissingPermissionsError>;
declare function checkAccess(permissions: Permissions, resource: string): Result<Access, InsuficientPermissionsError>;
const access = findUser('user_123')
.andThen(user =>
getUserPermissions(user)
.andThen(permissions =>
checkAccess(permissions, 'api-key')
)
);
Or with intermediate variables:
import { Result } from 'funkcia';
declare function findUser(id: string): Result<User, UserNotFound>;
declare function getUserPermissions(user: User): Result<Permissions, MissingPermissionsError>;
declare function checkAccess(permissions: Permissions, resource: string): Result<Access, InsuficientPermissionsError>;
const user = findUser('user_123');
const permissions = user.andThen(getUserPermissions);
const access = permissions.andThen(permissions => {
return checkAccess(permissions, 'admin-panel');
});
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