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Interactive REPL

The Prism REPL (Read-Eval-Print Loop) provides an interactive environment for experimenting with Prism code.

Accessing the REPL​

# Launch the REPL
prism

# Or explicitly
prism repl

Features​

Interactive Evaluation​

Type expressions and see immediate results with confidence tracking:

prism> 2 + 3
5 (number)

prism> "Hello" + " World"
Hello World (string)

prism> 42 ~> 0.85
42 (~0.85) (confident)

prism> x = 10
10 (number)

prism> x * 2
20 (number)

Multi-line Input​

The REPL automatically detects incomplete expressions:

prism> result = {
...>   value: 42,
...>   confidence: 0.9
...> }
{ value: 42, confidence: 0.9 } (object)

prism> uncertain if (result.confidence > 0.8) {
...>   high { "Very confident" }
...>   low { "Not confident" }
...> }
Very confident (string)

Variable Persistence​

Variables persist across REPL sessions:

prism> name = "Alice"
Alice (string)

prism> score = 95 ~> 0.9
95 (~0.9) (confident)

prism> greeting = "Hello, ${name}! Your score is ${score}"
Hello, Alice! Your score is 95 (string)

REPL Commands​

:help​

Display available commands and shortcuts:

prism> :help

🌟 Prism REPL Commands 🌟

:help     - Show this help message
:vars     - Display all variables in current session
:clear    - Clear all variables and reset session
:history  - Show command history
:stats    - Display session statistics
:llm      - Show LLM provider status
:exit     - Exit the REPL (or use Ctrl+D)

Tips:
- Use TAB for auto-completion (coming soon)
- Use UP/DOWN arrows for command history
- Multi-line expressions are supported
- Confidence values are shown as (~n.n)

:vars​

Show all variables in the current session:

prism> x = 10
10 (number)

prism> y = 20 ~> 0.8
20 (~0.8) (confident)

prism> name = "Prism"
Prism (string)

prism> :vars
Session Variables:
  x: 10
  y: 20 (~80.0%)
  name: Prism

:clear​

Reset the session and clear all variables:

prism> x = 42
42 (number)

prism> :clear
Session cleared.

prism> x
❌ Error: Undefined variable: x

:history​

View command history from the current session:

prism> :history
Command History:
  1. x = 10
  2. y = 20
  3. x + y
  4. llm("Hello")
  5. :history

:stats​

Display session statistics:

prism> :stats
Session Statistics:
  Total Evaluations: 15
  Successful: 13
  Errors: 2
  Variables: 5
  Uptime: 3m 42s

:llm​

Check LLM provider status:

prism> :llm
LLM Provider Status:
  Active Providers: claude, gemini
  Default Provider: claude
  
Available models:
  - claude: Claude 3 Opus
  - gemini: Gemini Pro
  - mock: Mock Provider (for testing)

:stream <prompt>​

Stream an LLM response without writing Prism code. Streaming can be cancelled with Ctrl+C.

prism> :stream Draft a haiku about autumn rain
Drafting a gentle haiku about the autumn rain...
Soft rain threads the dusk
Amber leaves whisper on stone
Evening sips the mist

Confidence: 0.86

:exit​

Exit the REPL:

prism> :exit
Goodbye! Thanks for using Prism. 🚀

You can also use Ctrl+D to exit.

LLM Integration​

The REPL fully supports LLM calls:

prism> response = llm("What is 2 + 2?")
The answer to 2 + 2 is 4. (confident)

prism> analysis = llm("Analyze sentiment: 'Great product!'") ~> 0.9
The sentiment is positive - the phrase "Great product!" expresses satisfaction and enthusiasm. (~0.9) (confident)

prism> uncertain if (analysis) {
...>   high { "Positive sentiment confirmed" }
...>   medium { "Likely positive" }
...>   low { "Unclear sentiment" }
...> }
Positive sentiment confirmed (string)

Advanced Usage​

Confidence Propagation​

Watch how confidence flows through operations:

prism> a = 100 ~> 0.9
100 (~0.9) (confident)

prism> b = 50 ~> 0.8
50 (~0.8) (confident)

prism> a + b
150 (~0.8) (confident)  // Uses minimum confidence

prism> a ~+ b
150 (~0.72) (confident) // Multiplies confidences

Pipeline Operations​

prism> data = "hello world"
hello world (string)

prism> data |> toUpperCase |> split(" ") |> join("-")
HELLO-WORLD (string)

prism> [1, 2, 3, 4, 5] |> filter(n => n > 2) |> map(n => n * 2)
[6, 8, 10] (array)

Error Recovery​

The REPL gracefully handles errors:

prism> x = 
❌ Error: Expected expression after '='

prism> invalid syntax here
❌ Error: Unexpected token 'syntax'

prism> 2 + 2  // REPL continues working
4 (number)

Configuration​

Setting Default LLM Provider​

prism> runtime.setDefaultLLMProvider("gemini")
Default LLM provider set to: gemini

prism> llm("test")  // Now uses Gemini
This is a test response from Gemini. (confident)

Custom Prompts​

prism> prompt = "You are a helpful assistant. "
You are a helpful assistant.  (string)

prism> llm(prompt + "What is Prism?")
Prism is a programming language designed for uncertainty-aware computing... (confident)

Tips and Tricks​

  1. Quick Testing: Use the REPL to test expressions before adding them to scripts
  2. Confidence Experiments: Try different confidence values to see how they propagate
  3. LLM Debugging: Test LLM prompts interactively before using in production
  4. Variable Inspection: Use :vars frequently to track your session state
  5. History Navigation: Use arrow keys to recall and modify previous commands

Integration with VS Code​

If you have the Prism VS Code extension installed, you can:

  1. Send selections from .prism files to the REPL
  2. Save REPL sessions as .prism files
  3. Get syntax highlighting in REPL output (coming soon)

Programmatic Usage​

The REPL can also be used programmatically:

import { PrismREPL } from '@prism-lang/repl';

const repl = new PrismREPL();

// Evaluate expressions
const result = await repl.evaluate('2 + 2');
console.log(result); 
// { success: true, value: '4', type: 'number' }

// Check variables
const vars = repl.getVariables();

// Get session stats
const stats = repl.getSessionStats();