JAF (Just Another Flow) is a powerful streaming data processing system for JSON/JSONL data with a focus on lazy evaluation, composability, and a fluent API.

• 🚀 Streaming Architecture - Process large datasets without loading everything into memory
• 🔗 Lazy Evaluation - Build complex pipelines that only execute when needed
• 🎯 Fluent API - Intuitive method chaining for readable code
• 🧩 Composable - Combine operations freely, integrate with other tools
• 📦 Multiple Sources - Files, directories, stdin, memory, compressed files, infinite streams
• 🛠️ Unix Philosophy - Works great with pipes and other command-line tools

pip install jaf

# Filter JSON data using S-expressions (lazy by default)
jaf filter users.jsonl '(gt? @age 25)'

# Or use JSON array syntax
jaf filter users.jsonl '["gt?", "@age", 25]'

# Or use infix DSL (note: paths need @ prefix)
jaf filter users.jsonl '@age > 25'

# Evaluate immediately with --eval
jaf filter users.jsonl '(gt? @age 25)' --eval

# Chain operations
jaf filter users.jsonl '(eq? @status "active")' | \
jaf map - "@email" | \
jaf eval -

# Complex queries with nested logic
jaf filter logs.jsonl '(and (eq? @level "ERROR") (gt? @timestamp "2024-01-01"))' --eval

# Combine with other tools
jaf filter logs.jsonl '(eq? @level "ERROR")' --eval | \
ja groupby service

from jaf import stream

# Build a pipeline
pipeline = stream("users.jsonl") \
    .filter(["gt?", "@age", 25]) \
    .map(["dict", "name", "@name", "email", "@email"]) \
    .take(10)

# Execute when ready
for user in pipeline.evaluate():
    print(user)

Operations don't execute until you call .evaluate() or use --eval:

# This doesn't read any data yet
pipeline = stream("huge_file.jsonl") \
    .filter(["contains?", "@tags", "important"]) \
    .map("@message")

# Now it processes data
for message in pipeline.evaluate():
    process(message)

JAF supports multiple query syntaxes for flexibility:

# Simple comparisons
(eq? @status "active")              # status == "active"
(gt? @age 25)                       # age > 25
(contains? @tags "python")          # "python" in tags

# Boolean logic
(and 
    (gte? @age 18)
    (eq? @verified true))

# Nested expressions
(or (eq? @role "admin") 
    (and (eq? @role "user") 
         (gt? @score 100)))

# Same queries in JSON array format
["eq?", "@status", "active"]
["gt?", "@age", 25]
["contains?", "@tags", "python"]

["and", 
    ["gte?", "@age", 18],
    ["eq?", "@verified", true]
]

# Natural infix notation (paths need @ prefix)
@status == "active"
@age > 25 and @verified == true
@role == "admin" or (@role == "user" and @score > 100)

All three syntaxes compile to the same internal representation. Use whichever feels most natural for your use case!

• filter - Keep items matching a predicate
• map - Transform each item
• take/skip - Limit or paginate results
• batch - Group items into chunks
• Boolean ops - AND, OR, NOT on filtered streams

• Getting Started - Installation and first steps
• API Guide - Complete Python API reference
• Query Language - Query syntax and operators
• CLI Reference - Command-line usage
• Cookbook - Practical examples

# Find errors in specific services
errors = stream("app.log.jsonl") \
    .filter(["and",
        ["eq?", "@level", "ERROR"],
        ["in?", "@service", ["api", "auth"]]
    ]) \
    .map(["dict", 
        "time", "@timestamp",
        "service", "@service",
        "message", "@message"
    ]) \
    .evaluate()

# Find invalid records
invalid = stream("users.jsonl") \
    .filter(["or",
        ["not", ["exists?", "@email"]],
        ["not", ["regex-match?", "@email", "^[^@]+@[^@]+\\.[^@]+$"]]
    ]) \
    .evaluate()

# Transform and filter data
pipeline = stream("raw_sales.jsonl") \
    .filter(["eq?", "@status", "completed"]) \
    .map(["dict",
        "date", ["date", "@timestamp"],
        "amount", "@amount",
        "category", ["if", ["gt?", "@amount", 1000], "high", "low"]
    ]) \
    .batch(1000)

# Process in chunks
for batch in pipeline.evaluate():
    bulk_insert(batch)

JAF works seamlessly with other tools:

# With jsonl-algebra
jaf filter orders.jsonl '["gt?", "@amount", 100]' --eval | \
ja groupby customer_id --aggregate 'total:amount:sum'

# With jq
jaf filter data.jsonl '["exists?", "@metadata"]' --eval | \
jq '.metadata'

# With standard Unix tools
jaf map users.jsonl "@email" --eval | sort | uniq -c

JAF is designed for streaming large datasets:

• Processes one item at a time
• Minimal memory footprint
• Early termination (e.g., with take)
• Efficient pipeline composition

JAF supports windowed operations for memory-efficient processing of large datasets:

• distinct, groupby, join, intersect, except all support window_size parameter
• Use window_size=float('inf') for exact results (default)
• Finite windows trade accuracy for memory efficiency
• Warning: For intersect/except, window size must be large enough to capture overlapping items

# Exact distinct (uses more memory)
stream("data.jsonl").distinct(window_size=float('inf'))

# Windowed distinct (bounded memory)
stream("data.jsonl").distinct(window_size=1000)

# Tumbling window groupby
stream("logs.jsonl").groupby(key="@level", window_size=100)

• Bloom Filters for memory-efficient approximate set operations (intersect, except, distinct)
• Count-Min Sketch for frequency estimation and heavy hitters detection
• HyperLogLog for cardinality estimation
• These would provide controllable accuracy/memory tradeoffs with theoretical guarantees

• Top-K operations - Find most frequent items in streams
• Sampling strategies - Reservoir sampling, stratified sampling
• Time-based windows - Process data in time intervals
• Exactly-once semantics - Checkpointing and recovery
• Parallel processing - Multi-threaded stream processing

• FastAPI - REST API for stream processing
• Model Context Protocol (MCP) - LLM integration
• Apache Kafka - Stream from/to Kafka topics
• Cloud Storage - S3, GCS, Azure Blob support

Contributions are welcome! Please read our Contributing Guide for details.

JAF is licensed under the MIT License. See LICENSE for details.

• jsonl-algebra - Relational operations on JSONL
• jq - Command-line JSON processor
• dotsuite - Pedagogical ecosystem demonstrating the concepts behind JAF through simple, composable tools. Great for understanding the theory and building blocks that JAF productionizes.