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Scallop REPL

sclrepl is the interactive Read-Eval-Print-Loop for Scallop, allowing you to experiment with Scallop programs interactively.

Starting the REPL

sclrepl

This starts an interactive session where you can enter Scallop declarations and queries.

Basic Usage

Entering Declarations

Type Scallop declarations directly:

scallop> rel edge = {(0, 1), (1, 2), (2, 3)}

Defining Rules

scallop> rel path(a, b) = edge(a, b)
scallop> rel path(a, c) = path(a, b), edge(b, c)

Querying Relations

scallop> query path
path: {(0, 1), (0, 2), (0, 3), (1, 2), (1, 3), (2, 3)}

REPL Commands

Special Commands

:help - Show available commands

scallop> :help

:quit or :exit - Exit the REPL

scallop> :quit

:clear - Clear all declarations

scallop> :clear

:provenance <type> - Change provenance

scallop> :provenance minmaxprob

:relations - List all relations

scallop> :relations

Interactive Workflow

Experimentation

scallop> rel number = {1, 2, 3, 4, 5}
scallop> rel square(n, n * n) = number(n)
scallop> query square
square: {(1, 1), (2, 4), (3, 9), (4, 16), (5, 25)}

Iterative Development

scallop> rel person = {"alice", "bob", "charlie"}
scallop> query person
person: {"alice", "bob", "charlie"}

scallop> rel friend(a, b) = person(a), person(b), a != b
scallop> query friend
friend: {("alice", "bob"), ("alice", "charlie"), ("bob", "alice"), ...}

Probabilistic Reasoning

scallop> :provenance minmaxprob
scallop> rel 0.8::edge(0, 1)
scallop> rel 0.9::edge(1, 2)
scallop> rel path(a, b) = edge(a, b)
scallop> query path
path: {0.8::(0, 1), 0.9::(1, 2)}

Tips and Tricks

Multi-line Input

Use \ for line continuation:

scallop> rel complicated_rule(x, y) = \
         some_relation(x), \
         another_relation(y), \
         x > y

Inspecting Relations

scallop> :relations
Available relations:
  - edge: (i32, i32)
  - path: (i32, i32)

Quick Testing

scallop> rel test = {1, 2, 3}
scallop> query test
test: {1, 2, 3}
scallop> :clear
scallop> # Start fresh

Common Use Cases

Learning Scallop

Quickly test syntax and semantics:

scallop> rel fact = {"a", "b", "c"}
scallop> query fact

Prototyping

Develop logic interactively before saving to files:

scallop> # Try different rule formulations
scallop> rel version1(x) = ...
scallop> query version1
scallop> # Refine
scallop> rel version2(x) = ...
scallop> query version2

Debugging

Test problematic rules in isolation:

scallop> :provenance unit
scallop> # Add minimal facts
scallop> rel edge = {(0, 1)}
scallop> # Test rule
scallop> rel path(a, b) = edge(a, b)
scallop> query path

Summary

  • Start: sclrepl
  • Enter declarations, rules, and queries interactively
  • Commands: :help, :quit, :clear, :provenance, :relations
  • Use for: Learning, prototyping, debugging
  • Multi-line: Use \ for continuation

For more details: