Go Compiler — Functional Operations PoC

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.

The |> pipe operator

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

Generic slice operations

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

Build

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 

Roadmap

#	Feature	Compiler phases touched	Status
1	|> pipe operator	scanner, parser	done
2	fn lambda shorthand (fn(x) x*2)	scanner, parser	planned
3	filter, fmap, reduce as builtins	types2, typecheck, walk	planned
4	Custom IR node (OPIPELINE or similar)	ir, walk	planned

---

The Go Programming Language

Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.

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

Our canonical Git repository is located at https://go.googlesource.com/go. There is a mirror of the repository at https://github.com/golang/go.

Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.

Download and Install

Binary Distributions

Official binary distributions are available at https://go.dev/dl/.

After downloading a binary release, visit https://go.dev/doc/install for installation instructions.

Install From Source

If a binary distribution is not available for your combination of operating system and architecture, visit https://go.dev/doc/install/source for source installation instructions.

Contributing

Go is the work of thousands of contributors. We appreciate your help!

To contribute, please read the contribution guidelines at https://go.dev/doc/contribute.

Note that the Go project uses the issue tracker for bug reports and proposals only. See https://go.dev/wiki/Questions for a list of places to ask questions about the Go language.