A fork of the Go compiler used as a learning sandbox to explore how the compiler is structured by adding functional programming features from scratch.

This fork adds a |> pipe operator to Go. It lets you chain function calls left-to-right instead of nesting them right-to-left.

// without pipe
result := reduce(fmap(filter(xs, isEven), double), 0, add)

// with pipe
result := xs |> filter(isEven) |> fmap(double) |> reduce(0, add)

xs |> f(args...) is syntactic sugar for f(xs, args...). The transformation happens at parse time — the rest of the compiler sees ordinary function calls.

Rules:

• Left-associative: a |> f |> g → g(f(a))
• Lowest precedence: a + b |> f(c) → f(a+b, c)
• Works with any function, including generics and builtins

The pipe operator pairs naturally with generic helper functions:

func filter[T any](s []T, f func(T) bool) []T
func fmap[T, U any](s []T, f func(T) U) []U
func reduce[T, U any](s []T, init U, f func(U, T) U) U

xs := []int{1, 2, 3, 4, 5}

// filter: keep evens
evens := xs |> filter(func(x int) bool { return x%2 == 0 })
// → [2 4]

// fmap: int → string (cross-type)
strs := xs |> fmap(func(x int) string { return fmt.Sprintf("<%d>", x) })
// → [<1> <2> <3> <4> <5>]

// reduce: sum
sum := xs |> reduce(0, func(acc, x int) int { return acc + x })
// → 15

// chained pipeline
result := xs |>
    filter(func(x int) bool { return x%2 != 0 }) |>
    fmap(func(x int) int { return x * x }) |>
    reduce(0, func(acc, x int) int { return acc + x })
// sum of squares of odds: 1 + 9 + 25 = 35

Requires an existing Go toolchain to bootstrap:

cd src && ./make.bash

Run a program with the modified compiler:

./bin/go run yourfile.go

To run the test case above just run:

./bin/go run src/cmd/compile/internal/syntax/testdata/pipe.go 

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Gopher image by Renee French, licensed under Creative Commons 4.0 Attribution license.

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