Debug overview
Helpers for debugging applications during development. These should be assumed to be unsafe and shouldn’t make their way into production code.
Added in v0.2.0
Table of contents
3 Functions
trace
Log the provided string to the console and immediately return the generic argument. This is useful in the middle of pipe/flow chains.
The trace function should only be used for debugging. The function is not referentially transparent: its type indicates that it is a pure function but it has the side effect of outputting the trace message.
Signature
export declare const trace: (msg: string) => <A>(x: A) => A
trace :: string -> a -> a
Example
import { trace } from 'fp-ts-std/Debug'
import { flow } from 'fp-ts/function'
const double = (n: number): number => n * 2
const toString = (n: number): string => String(n)
// Will log: "my log message"
const doubledString: (n: number) => string = flow(double, trace('my log message'), toString)
// Actual function/pipeline behaviour is unaffected:
assert.strictEqual(doubledString(2), '4')
Added in v0.2.0
traceShowWithValue
Like traceWithValue, but first processes the value via Show.
Signature
export declare const traceShowWithValue: <A>(S: Show<A>) => (msg: string) => (x: A) => A
traceShowWithValue :: Show a -> string -> a -> a
Example
import { traceShowWithValue } from 'fp-ts-std/Debug'
import { flow } from 'fp-ts/function'
import * as Num from 'fp-ts/number'
const double = (n: number): number => n * 2
const toString = (n: number): string => String(n)
// Will log: "my log message: <Shown value>"
const doubledString: (n: number) => string = flow(double, traceShowWithValue(Num.Show)('my log message: '), toString)
// Actual function/pipeline behaviour is unaffected:
assert.strictEqual(doubledString(2), '4')
Added in v0.16.0
traceWithValue
Like trace, but logs the generic value too.
Signature
export declare const traceWithValue: (msg: string) => <A>(x: A) => A
traceWithValue :: string -> a -> a
Example
import { traceWithValue } from 'fp-ts-std/Debug'
import { flow } from 'fp-ts/function'
const double = (n: number): number => n * 2
const toString = (n: number): string => String(n)
// Will log: "my log message: <value>"
const doubledString: (n: number) => string = flow(double, traceWithValue('my log message: '), toString)
// Actual function/pipeline behaviour is unaffected:
assert.strictEqual(doubledString(2), '4')
Added in v0.2.0