2026-01-02

Fixing the 'using' Directive Bug and Adding HTTP Status Code Constants in EZ Language

Overview

I contributed to EZ, which is a modern programming language built with Go. I worked on two related issues: adding HTTP status code constants to the @http module (Issue #901) and fixing a bug where the using directive did not bring stdlib constants into scope (Issue #909).

Background: What is the using Directive?

In EZ, you can import modules and use them with a namespace prefix:

import @http

do main() {
    println("${http.OK}")  // Works: 200
}

The using directive allows you to access module exports without the prefix:

import @std
using std

do main() {
    println("Hello")  // No need for std.println
}

The Problem

Issue #901: Need for HTTP Status Code Constants

Users had to use raw integers for HTTP status code comparisons:

if response.status == 200 {
    // ...
}

This is not readable. We wanted to support named constants like:

if response.status == http.OK {
    // ...
}

Issue #909: using Directive Only Works for Functions

After implementing the HTTP constants, we discovered a bigger problem. The using directive did not bring constants into scope:

import @http
using http

do main() {
    println("${OK}")        // Error: undefined variable 'OK'
    println("${http.OK}")   // Works: 200
}

This bug affected all stdlib modules with constants:

  • @http - OK, CREATED, NOT_FOUND, etc.
  • @os - MAC_OS, LINUX, WINDOWS
  • @math - PI, E, PHI, SQRT2
  • @time - SUNDAY, MONDAY, JANUARY, HOUR, DAY
  • @io - READ_ONLY, WRITE_ONLY, SEEK_START
  • @db - ALPHA, NUMERIC, KEY_LEN
  • @uuid - NIL

My Solution

I solved both issues with a two-part approach.

Part 1: Adding HTTP Status Code Constants (#907)

First, I added HTTP status code constants to pkg/stdlib/http.go:

const (
    OK                    int64 = 200
    CREATED               int64 = 201
    ACCEPTED              int64 = 202
    NO_CONTENT            int64 = 204
    BAD_REQUEST           int64 = 400
    UNAUTHORIZED          int64 = 401
    FORBIDDEN             int64 = 403
    NOT_FOUND             int64 = 404
    INTERNAL_SERVER_ERROR int64 = 500
    // ... and more
)

Then I exposed these as builtins in the HttpBuiltins map:

"http.OK": {
    Fn: func(args ...object.Object) object.Object {
        return &object.Integer{Value: big.NewInt(OK)}
    },
},

Part 2: Fixing the using Directive Bug (#979)

The core problem was in the type checker. It only checked for functions when validating identifiers accessed via using, not constants.

Step 1: Add IsConstant flag to all stdlib constants

I added an IsConstant: true flag to distinguish constants from functions:

"http.OK": {
    Fn: func(args ...object.Object) object.Object {
        return &object.Integer{Value: big.NewInt(OK)}
    },
    IsConstant: true,  // Added this flag
},

I applied this to all constants across 7 stdlib modules: db.go, http.go, io.go, math.go, os.go, time.go, and uuid.go.

Step 2: Add isStdlibConstant() function to type checker

I added a new function in pkg/typechecker/typechecker.go to check if an identifier is a stdlib constant:

func (tc *TypeChecker) isStdlibConstant(moduleName, constName string) bool {
    stdConsts := map[string]map[string]bool{
        "http": {
            "OK": true, "CREATED": true, "BAD_REQUEST": true,
            "NOT_FOUND": true, "INTERNAL_SERVER_ERROR": true,
            // ... all HTTP constants
        },
        "os": {
            "MAC_OS": true, "LINUX": true, "WINDOWS": true,
            "CURRENT_OS": true,
        },
        "math": {
            "PI": true, "E": true, "PHI": true, "SQRT2": true,
        },
        // ... other modules
    }
    if modConsts, ok := stdConsts[moduleName]; ok {
        return modConsts[constName]
    }
    return false
}

Step 3: Update isKnownIdentifier() to check constants

I modified the isKnownIdentifier() function to also check stdlib constants when using is declared:

// Check if it's a stdlib constant accessible via 'using'
for moduleName := range tc.fileUsingModules {
    if tc.isStdlibConstant(moduleName, name) {
        return true
    }
}
if tc.currentScope != nil {
    for moduleName := range tc.currentScope.usingModules {
        if tc.isStdlibConstant(moduleName, name) {
            return true
        }
    }
}

Step 4: Add unit tests for each module

I wrote unit tests to verify the fix works for all stdlib constants:

func TestHttpModuleConstantWithoutModuleNamespace(t *testing.T) {
    input := `
import @http
using http

do main() {
    const status_200 int = OK
    const status_404 int = NOT_FOUND
    const status_500 int = INTERNAL_SERVER_ERROR
}
`
    tc := typecheck(t, input)
    assertNoErrors(t, tc)
}

Result

The changes were merged in PR #907 and PR #979.

What was achieved:

  • New Feature: Users can now use readable HTTP status code constants (http.OK, http.NOT_FOUND, etc.)
  • Bug Fix: The using directive now correctly brings all stdlib constants into scope
  • Consistency: Constants now work the same way as functions with using
  • Test Coverage: Added unit tests for all stdlib module constants

Now users can write clean code like:

import @http
using http

do main() {
    temp resp, err = http.get("https://api.example.com")
    if resp.status == OK {
        println("Success!")
    } else if resp.status == NOT_FOUND {
        println("Resource not found")
    }
}

This was a great experience contributing to a programming language project and understanding how type checkers validate identifiers!

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