Franz — Functional, Prototype‑Oriented Programming Language

Franz is a high level, functional, interpreted, dynamically typed, general-purpose programming language, with a terse syntax, and a verbose standard library.

Rust-like safety without the complexity

Tiny, keyword‑free functional core with prototype‑oriented objects, capability‑safe effects, and deterministic replay.

It features:

Strictly no side effects* to help you write functional code
The ability to localize the effects of imported Franz files.
LLVM Native Compilation - Direct compilation to native executables via LLVM IR (s 1-3 complete)
List Literals (LLVM) - Industry-standard heterogeneous lists with bracket syntax: [1, "hello", 3.14], nested lists: [[1,2],[3,4]] ( complete, 9/9 tests passing)
List Operations (LLVM) - 7 list operations: head, tail, cons, empty?, length, nth, is_list - all working with Generic* pointers (Rust-style)
Comparison Operators (LLVM) - Equality and ordering: is, less_than, greater_than for integers, floats, and strings ( complete, 35/35 tests passing — now also tracks void separately from numeric zero)
Enhanced Math Functions (LLVM) - 10 mathematical functions: remainder, power, random, floor, ceil, round, abs, min, max, sqrt ( complete, 27/27 tests passing)
Control Flow (LLVM) - if/when/unless statements and cond chains for pattern matching (-5.5 complete, 65+ tests passing)
Type Guards (LLVM) - Compile-time type checking: is_int, is_float, is_string, is_list ( complete, 30/30 tests passing)
Cond Chains - Pattern matching conditionals like Lisp/Scheme for elegant multi-way branching ( complete, 30/30 tests passing)
Native Code Performance - Rust-level performance with automatic type conversion, constant folding, and LLVM optimizations
Lexical scoping - Industry-standard lexical scoping with snapshot-based closures ( complete)
Arbitrary-depth nested closures - Full support for 3+ level nested closures (critical fix in )
Full stdlib closure support - All higher-order functions work with closures ( complete, 48/48 tests passing)
Zero-leak closures - closures with reference counting (0.08% memory leak rate)
Comprehensive examples & tests - 6 examples + 12 smoke tests demonstrating scoping patterns
High-performance module caching - 118k+ cached loads/second with AST-level caching
Namespace isolation - Safe multi-library usage with use_as() and dot notation
Capability-based security - Sandboxed execution with use_with() prevents RCE vulnerabilities
Circular dependency detection - Import stack tracking prevents stack overflow crashes
Industry-standard error handling - try/catch/error system without process termination
Standard Library - String Module - 10 string manipulation functions (uppercase, lowercase, trim, split, replace, repeat, starts_with, ends_with, contains, char_at)
Standard Library - Math Module - 15 mathematical functions and constants (PI, E, abs, sqrt, floor, ceil, round, max, min, clamp, sum, average, median, factorial, gcd)
Standard Library - List Module - 12 advanced list operations (reverse, unique, flatten, zip, take, drop, any, all, partition, filled, chunk, sort)
Standard Library - Func Module - 7 higher-order function combinators (compose2, identity, constant, flip, apply, apply_twice, apply_n)
Dynamic typing and garbage collection.
0 keywords, everything is a function.

*With the exception of IO

table = (map (range 10) {_ y ->
  <- (map (range 10) {item x ->
    <- (multiply (add x 1) (add y 1))
  })
})

From examples/mult-table.franz

From examples/game-of-life.franz

Lexical Scoping

Franz now features industry-standard lexical scoping with arbitrary-depth nested closures (s 3-5 complete).

What is lexical scoping?

Functions capture variables from their definition-time environment (not call-time)
Closures maintain independent captured environments
Predictable, isolated function behavior
Full nested closure support (3, 4, 5+ levels deep)

Basic Example:

x = 10
get_x = {-> <- x}  // Captures x=10

test = {->
  x = 20           // Local x in test's scope
  <- (get_x)       // Returns 10 (captured value)
}

(println (test))   // Output: 10

Nested Closure Example ():

// Three-level nested closure
level1 = {->
  a = 1
  level2 = {->
    b = 2
    level3 = {->
      c = 3
      <- (add (add a b) c)  // ✅ Can access a, b, and c
    }
    <- level3
  }
  <- level2
}

result = (((level1)))  // Returns 6 (1+2+3)

Smoke Tests & Examples:

# Run automated smoke tests (12 tests)
bash scripts/run-smoke-tests.sh

# Run scoping examples
./franz --scoping=lexical examples/scoping/lexical/working/01-basic-closure.franz
./franz --scoping=lexical examples/scoping/lexical/working/02-nested-closures.franz
./franz --scoping=lexical examples/scoping/lexical/patterns/01-partial-application.franz

Dynamic scoping (legacy mode):

./franz --scoping=dynamic program.franz

Control Flow and Pattern Matching

Franz features industry-standard control flow with LLVM native compilation (s 5.1-5.5 complete).

If/When/Unless Statements

If Statement:

// Basic if-then-else
result = (if (greater_than x 10) "big" "small")

// Optional else (returns 0 if false)
bonus = (if (greater_than score 80) 10)

// Multi-statement blocks
result = (if condition
  {
    (println "Debug: condition true")
    temp = (compute_value)
    <- temp
  }
  {<- default_value})

When/Unless Helpers:

// When: execute if condition true
bonus = (when (greater_than score 80) 10)

// Unless: execute if condition false
safe_divide = (unless (is divisor 0) (divide 100 divisor))

Cond Chains (Pattern Matching)

Lisp/Scheme-style pattern matching conditionals:

// Grade classification
grade = (cond
  ((greater_than score 89) "A")
  ((greater_than score 79) "B")
  ((greater_than score 69) "C")
  ((greater_than score 59) "D")
  (else "F"))

// HTTP status codes
message = (cond
  ((is code 200) "OK")
  ((is code 404) "Not Found")
  ((is code 500) "Server Error")
  (else "Unknown"))

// Age brackets
bracket = (cond
  ((less_than age 18) "minor")
  ((less_than age 30) "young adult")
  ((less_than age 50) "middle age")
  (else "senior"))

Features:

Early exit on first match
Unlimited clauses
Optional else for default value
Returns 0 if no match and no else
C-level performance (zero overhead)

Type Guards

Compile-time type checking:

// Type-based branching
action = (cond
  ((is_int x) (multiply x 2))
  ((is_float x) (multiply x 1.5))
  ((is_string x) (join x "!"))
  (else 0))

// Type-safe operations
safe_add = (if (and (is_int a) (is_int b))
  (add a b)
  0)

Available Type Guards:

(is_int value) - Check if integer (i64)
(is_float value) - Check if float (double)
(is_string value) - Check if string (i8*)

Building Franz

Build the interpreter (excludes franz-check tool)

find src -name "*.c" -not -name "check.c" | xargs gcc -Wall -lm -o franz

Alternative: Include all source files

gcc src/*.c -Wall -lm -o franz

Debug build (for memory testing)

find src -name "*.c" -not -name "check.c" | xargs gcc -g -Wall -lm -o franz

Running Examples

Basic execution:

Run any example

./franz examples/hello-world.franz ./franz examples/fizzbuzz.franz

Debug mode (shows tokens, AST, evaluation, scoping mode)

./franz -d examples/hello-world.franz

Check version

./franz -v

Use dynamic scoping (legacy mode)

./franz --scoping=dynamic examples/your-program.franz

Set scoping via environment variable

FRANZ_SCOPING=lexical ./franz examples/your-program.franz

Pipe code directly:

echo '(print "Hello Franz!")' | ./franz echo '(print (add 5 3))' | ./franz echo '(println "Hello with newline")' | ./franz

Available Examples

The examples/ directory contains 19 Franz programs:

hello-world.franz - Simple output
fizzbuzz.franz - Classic FizzBuzz algorithm
factorial.franz - Interactive factorial calculator
fibonacci.franz - Fibonacci sequence generator
arithmetic.franz - Armstrong numbers
collatz.franz - Collatz conjecture
game-of-life.franz - Conway's Game of Life
cube.franz - 3D cube rendering
car.franz - Car simulation
fish.franz - Fish animation
And more...

Testing Different Types

Non-interactive examples (run directly): ./franz examples/hello-world.franz ./franz examples/fizzbuzz.franz ./franz examples/10-print.franz
Interactive examples (require user input): ./franz examples/factorial.franz ./franz examples/fibonacci.franz
Complex programs (graphics/animations): ./franz examples/game-of-life.franz ./franz examples/cube.franz ./franz examples/fish.franz

Franz uses S-expression syntax (function arg1 arg2) and supports dynamic typing with strings, integers, floats, functions, lists, and void types.

Getting Started

Install

Basics

All function calls are done with s-expressions (think lisp). For example,

(print "hello world")

In this case, the function print is applied with the string "hello world" as an argument.

Recursion

No rec keyword needed — functions are recursive by default.

factorial = {n ->
  <- (if (is n 0) {<- 1} {<- (multiply n (factorial (subtract n 1)))})
}
(println "factorial 5 =" (factorial 5))

All data in franz is one of 6 different types:

string
integer
float
function / native function
list
void

We can store this data in variables, for example,

a = 5
b = "hello"

We can combine data together to form lists,

magic_list = (list 123 "hello" 42.0)

Lists are always passed by value.

We can encapsulate code in functions using curly braces,

f = {
  (print "Funky!")
}

(f) // prints "Funky"

Functions can get arguments, denoted using the "->" symbol. For example,

add_two_things = {a b ->
  (print (add a b))
}

(add_two_things 3 5) // prints 8

They can also return values using the "<-" symbol,

geometric_mean = {a b ->
  <- (power (multiply a b) 0.5)
}

(print (geometric_mean 3 5) "\n") // prints 3.87...

Functions operate in a few important ways:

Function applications are dynamically scoped.
Functions cannot create side effects.
Like in JavaScript and Python, all functions are first-class.

Most of the features you may expect in a programming language are implemented in the form of functions. For example, here is a Fizzbuzz program using the add, loop, if, remainder, is, and print functions,

(loop 100 {i ->
  i = (add i 1)

  (if (is (remainder i 15) 0) {
      (print "fizzbuzz\n")
    } (is (remainder i 3) 0) {
      (print "fizz\n")
    } (is (remainder i 5) 0) {
      (print "buzz\n")
    } {(print i "\n")}
  )
})

From examples/fizzbuzz.franz

You should now be ready to write your own Franz programs! More info on how to build applications with events, files, code-splitting, and more, is found in the standard library documentation below.

Standard Library

IO

arguments
- A list command line arguments, like argv in C.
- Will skip all arguments up to and including the path to the franz program.
(print arg1 arg2 arg3 ...)
- Prints all arguments to stdout, returns nothing.
(println arg1 arg2 arg3 ...)
- Prints all arguments separated by a single space and appends a newline. Useful for clean line output when piping.
- Important: Arguments must be separated by spaces, not commas. Franz has no commas in syntax.
- Example: (println "Name:" name "Age:" age) ✅
- Wrong: (println "Name:", name, "Age:", age) ❌ (commas treated as undefined identifiers)
(input)
- Gets a line of input from stdin.
(rows)
- Returns the number of rows in the terminal.
(columns)
- Returns the number of columns in the terminal.
(read_file path)
- Returns the contents of the file designated by path, in a string. If the file cannot be read, returns void.
- path: string
(write_file path contents)
- Writes the string contents into the file designated by path, returns nothing.
- path: string
- contents: string
(event time) or (event)
- Returns the ANSI string corresponding with the current event. This may block for up to time seconds, rounded up to the nearest 100 ms. If no time is supplied, the function will not return before receiving an event.
- time: integer or float
(use path1 path2 path3 ... fn)
- Franz's code splitting method. Runs code in file paths, in order, on a new scope. Then uses said scope to apply fn.
- path1, path2, path3, ...: string
- fn: function
(shell command)
- Runs command as an sh program in a seperate process, and returns stdout of the process as a string.
- command: string

Comparisons

(is a b)
- Checks if a and b are equal, returns 1 if so, else returns 0. If a and b are lists, a deep comparison is made.
- Safe void handling: (is value void) works for literals, variables, and closure parameters without ever conflating void with numeric 0.
(less_than a b)
- Checks if a is less than b, returns 1 if so, else returns 0.
- a: integer or float
- b: integer or float
(greater_than a b)
- Checks if a is greater than b, returns 1 if so, else returns 0.
- a: integer or float
- b: integer or float

Logical Operators

(not a)
- Returns 0 if a is 1, and 1 if a is 0.
- a: integer, which is 1 or 0
(and arg1 arg2 arg3 ...)
- Returns 1 if all arguments are 1, else returns 0
- arg1, arg2, arg3, ...: integer, which is 1 or 0
(or arg1 arg2 arg3 ...)
- Returns 1 if at least one argument is 1, else returns 0
- arg1, arg2, arg3, ...: integer, which is 1 or 0

Arithmetic

(add arg1 arg2 arg3 ...)
- Returns arg1 + arg2 + arg3 + ...
- Requires a minimum of two args
- arg1, arg2, arg3, ...: integer or float
(subtract arg1 arg2 arg3 ...)
- Returns arg1 - arg2 - arg3 - ...
- Requires a minimum of two args
- arg1, arg2, arg3, ...: integer or float
(divide arg1 arg2 arg3 ...)
- Returns arg1 / arg2 / arg3 / ...
- Requires a minimum of two args
- arg1, arg2, arg3, ...: integer or float
(multiply arg1 arg2 arg3 ...)
- Returns arg1 * arg2 * arg3 * ...
- Requires a minimum of two args
- arg1, arg2, arg3, ...: integer or float
(remainder a b)
- Returns the remainder of a and b.
- a: integer or float
- b: integer or float
(power a b)
- Returns a to the power of b.
- a: integer or float
- b: integer or float
(random)
- Returns a random number from 0 to 1.

Control

(loop count fn)
- Applies fn, count times. If fn returns, the loop breaks, and loop returns whatever fn returned, else repeats until loop is completed.
- count: integer, which is greater than or equal to 0
- fn: function, which is in the form {n -> ...}, where n is the current loop index (starting at 0).
(until stop fn initial_state) or (until stop fn)
- Applies fn, and repeats until fn returns stop. until returns whatever fn returned, before stop.
- The return value of every past iteration is passed on to the next. The initial iteration uses initial_state if supplied, or returns void if not.
- fn: function, which is in the form {state n -> ...}, where n is the current loop index (starting at 0), and state is the current state.
(if condition1 fn1 condtion2 fn2 condtion3 fn3 ... fn_else)
- If condition1 is 1, applies fn1.
- Else if condition2 is 1, applies fn2, else if ...
- If no condtions were 1, applies fn_else.
- Return whatever the result of fn1, fn2, fn3, ..., or fn_else was.
- condition1, condition2, condition3, ...: integer, which is 1 or 0
- fn1, fn2, fn3, ..., fn_else: function, which takes no arguments
(wait time)
- Blocks execution for time amount of seconds.
- time: integer or float.

Types

void
- A value of type void
(integer a)
- Returns a as an integer.
- a: string, float, or integer.
(string a)
- Returns a as a string.
- a: string, float, or integer.
(float a)
- Returns a as a float.
- a: string, float, or integer.
(type a)
- Returns the type of a as a string.

List and String

(list arg1 arg2 arg3 ...)
- Returns a list, with the arguments as it's contents.
(length x)
- Returns the length of x
- x: string or list.
(join arg1 arg2 arg3 ...)
- Returns all args joined together.
- All args must be of the same type.
- arg1, arg2, arg3, ...: string or list.
(get x index1) or (get x index1 index2)
- Returns the item in x at index1. If x is a string, this is a single char.
- If index2 is supplied, returns a sub-array or substring from index1 to index2, not including index2.
- x: string or list.
- index1: int.
- index2: int.
(insert x item) or (insert x item index)
- Returns a list or string, in which item was inserted into x at index. Does not overwrite any data.
- If index not supplied, item is assumed to be put at the end of x.
- x: string or list.
- item: string if x is string, else any
- index: int.
(set x item index)
- Returns a list or string, in which the item located at index in x, was replaced by item.
- x: string or list.
- item: string if x is string, else any
- index: int.
(delete x index1) or (delete x index1 index2)
- Returns a string or list, where index1 was removed from x.
- If index2 is supplied, all items from index1 to index2 are removed, not including index2.
- x: string or list.
- index1: int.
- index2: int.
(map arr fn)
- Returns a list created by calling fn on every item of arr, and using the values returned by fn to populate the returned array.
- arr: list
- fn: function, which is in the form {item i -> ...}, where item is the current item, and i is the current index.
(reduce arr fn initial_acc) or (reduce arr fn)
- Returns a value, computed via running fn on every item in arr. With every iteration, the last return from fn is passed to the next application of fn. The final returned value from fn is the value returned from reduce.
- arr: list.
- fn: function, which is in the form {acc item i -> ...}, where item is the current item, acc is the accumulator (the result of fn from the last item), and i is the current index. acc is initial_acc if supplied, or void if not.
(filter arr fn)
- Returns a new list containing only the elements from arr where fn returns a truthy value (non-zero).
- arr: list
- fn: function, which is in the form {item i -> ...}, where item is the current item, and i is the current index. Must return an integer (0 for false, non-zero for true).
- Example: (filter (list 1 2 3 4 5 6) {x i -> <- (is (remainder x 2) 0)}) returns [List: 2, 4, 6]
(range n)
- Returns a list with the integers from 0 to n, not including n.
- n: integer, which is greater than or equal to 0.
(find x item)
- Returns the index of item in x. Returns void if not found.
- x: string or list
- item: string if x is string, else any

List Helpers (Recursive Programming)

(head lst)
- Returns the first element of lst, or void if empty.
- Useful for recursive list processing.
- lst: list
(tail lst)
- Returns all but the first element of lst as a new list.
- Returns empty list if lst has 0 or 1 elements.
- Useful for recursive list processing.
- lst: list
(cons item lst)
- Prepends item to the beginning of lst, returns new list.
- Equivalent to (insert lst item 0) but more idiomatic.
- item: any
- lst: list
(empty? lst)
- Returns 1 if lst is empty, 0 otherwise.
- Useful for checking base case in recursive functions.
- lst: list

Example: Recursive list processing

// Sum all elements in a list
sum = {lst ->
  <- (if (empty? lst)
    {<- 0}
    {<- (add (head lst) (sum (tail lst)))}
  )
}

(println (sum (list 1 2 3 4 5)))  // Prints: 15

Dictionary (Record) Functions

Dictionaries provide immutable key-value storage for structured data (similar to records/objects in other languages). Implemented using native hash table (TYPE_DICT) with O(1) average-case lookups.

(dict key1 val1 key2 val2 ...)
- Creates a dictionary from alternating keys and values using native hash table
- Keys can be any type (typically strings or integers)
- Values can be any type
- Performance: O(1) average-case lookups with FNV-1a hash function
- Example: (dict "name" "Ada" "age" 37) creates {name: Ada, age: 37}
(dict_get dict key)
- Returns the value associated with key, or void if not found
- dict: dict (native TYPE_DICT hash table)
- key: any type
- Performance: O(1) average-case lookup
- Example: (dict_get user "name") returns "Ada"
(dict_set dict key value)
- Returns a new dictionary with the key-value pair added/updated (immutable)
- Original dict unchanged
- dict: dict (hash table)
- key: any type
- value: any type
- Example: user2 = (dict_set user "age" 38) creates updated dict
(dict_keys dict)
- Returns a list of all keys in the dictionary
- dict: dict (hash table)
- Performance: O(n) iteration
- Example: (dict_keys user) returns [name, age]
(dict_values dict)
- Returns a list of all values in the dictionary
- dict: dict (hash table)
- Performance: O(n) iteration
- Example: (dict_values user) returns [Ada, 37]
(dict_has dict key)
- Returns 1 if key exists in dict, 0 otherwise
- dict: dict (hash table)
- key: any type
- Performance: O(1) average-case lookup
- Example: (dict_has user "name") returns 1
(dict_merge dict1 dict2)
- Returns a new dictionary combining all keys from both dicts
- If a key exists in both, dict2's value takes precedence
- dict1: dict (base dictionary)
- dict2: dict (override dictionary)
- Performance: O(n+m) where n, m are dict sizes
- Example: (dict_merge defaults user_config)
(dict_remove dict key)
- Returns a new dictionary with the key removed (immutable)
- Original dict unchanged
- dict: dict (hash table)
- key: any type
- Example: user2 = (dict_remove user "age")
(dict_map dict fn)
- Returns a new dictionary with all values transformed by fn
- Keys remain unchanged
- dict: dict (hash table)
- fn: function with signature {key value -> new_value}
- Performance: O(n) iteration with function application
- Example: boosted = (dict_map scores {k v -> <- (add v 5)})
(dict_filter dict fn)
- Returns a new dictionary containing only pairs where fn returns truthy
- dict: dict (hash table)
- fn: function with signature {key value -> boolean} (0=false, non-zero=true)
- Performance: O(n) iteration with predicate evaluation
- Example: high = (dict_filter scores {k v -> <- (greater_than v 90)})

Example: User record

// Create user
user = (dict
  "name" "Ada Lovelace"
  "age" 36
  "occupation" "Mathematician")

// Access
(println "Name:" (dict_get user "name"))  // Ada Lovelace

// Update (immutable)
user2 = (dict_set user "age" 37)

// Check existence
(if (dict_has user "email") {
  (println "Email:" (dict_get user "email"))
} {
  (println "No email address")
})

// Merge configs
defaults = (dict "timeout" 60 "debug" 0)
config = (dict_merge defaults (dict "debug" 1 "port" 8080))

For comprehensive documentation, see:

docs/dict/dict.md - Complete dict documentation
examples/dict/working/ - Working examples
test/dict/dict-test.franz - Test suite with 15 test cases

Function Composition

(pipe value fn1 fn2 fn3 ... fnN)
- Threads a value through a sequence of functions left-to-right. Each function receives the result of the previous function as its single argument.
- Provides a clean alternative to nested function calls or intermediate variables.
- Returns the final result after all transformations.
- value: any type
- fn1, fn2, ..., fnN: functions that each accept one argument

Example: Data transformation pipeline

// Without pipe - nested and hard to read
result = (subtract (multiply (add 5 3) 2) 4)

// With pipe - clear left-to-right flow
result = (pipe 5
  {x -> <- (add x 3)}       // 5 + 3 = 8
  {x -> <- (multiply x 2)}   // 8 * 2 = 16
  {x -> <- (subtract x 4)})  // 16 - 4 = 12

(println result)  // Prints: 12

Example: List processing pipeline

// Calculate sum of squares
numbers = (list 1 2 3 4 5)

result = (pipe numbers
  {lst -> <- (map lst {x i -> <- (multiply x x)})}
  {lst -> <- (reduce lst {acc x i -> <- (add acc x)} 0)})

(println result)  // Prints: 55 (1+4+9+16+25)

Example: Reusable named functions

double = {x -> <- (multiply x 2)}
add_ten = {x -> <- (add x 10)}
halve = {x -> <- (divide x 2)}

result = (pipe 20 double add_ten halve)
(println result)  // Prints: 25

Note: Franz's collection function callbacks require specific arities:

map: {item index -> ...}

reduce: {accumulator item index -> ...}

filter: {item index -> boolean}

Partial Application

(partial function arg1 arg2 ... argN) - Creates a partially applied function with fixed arguments
(call partial_fn new_args...) - Applies a partial function with additional arguments

Partial application allows you to "fix" some arguments of a function, creating a new specialized function that remembers those arguments.

Example: Creating specialized functions

// Create reusable functions
add_ten = (partial add 10)
double = (partial multiply 2)
half = (partial divide 2)

// Use with call
(println (call add_ten 5))    // 15 (add 10 5)
(println (call double 21))    // 42 (multiply 2 21)
(println (call half 100))     // 0.02 (divide 2 100)

Example: Multiple fixed arguments

add_many = (partial add 10 20 30)
(println (call add_many 40))  // 100 (10+20+30+40)

Example: With pipe for clean pipelines

add_ten = (partial add 10)
times_three = (partial multiply 3)

result = (pipe 5
  {x -> <- (call add_ten x)}
  {x -> <- (call times_three x)})

(println result)  // 45 ((5 + 10) * 3)

Example: Reusing partials

add_hundred = (partial add 100)
(call add_hundred 1)    // 101
(call add_hundred 50)   // 150
(call add_hundred 200)  // 300

Argument Order: Fixed args come FIRST: (partial fn A) creates {x -> (fn A x)}

(partial subtract 10) = {x -> (subtract 10 x)} = 10 - x

(partial divide 100) = {x -> (divide 100 x)} = 100 / x

Threading Macros

(thread-first value form1 form2 ...) - Threads value through forms, inserting as FIRST argument
(thread-last value form1 form2 ...) - Threads value through forms, inserting as LAST argument

Threading macros provide clean, linear data flow by automatically inserting values into function calls.

Example: Thread-first

// Without threading (nested)
result = (add (multiply (subtract 100 20) 2) 10)

// With thread-first (linear, left-to-right)
result = (thread-first 100
  (list subtract 20)    // 100 - 20 = 80
  (list multiply 2)     // 80 * 2 = 160
  (list add 10))        // 160 + 10 = 170

Example: Mathematical formula

// Calculate: ((x + 3) * 2) - 4
result = (thread-first 5
  (list add 3)          // 5 + 3 = 8
  (list multiply 2)     // 8 * 2 = 16
  (list subtract 4))    // 16 - 4 = 12

Example: String building

result = (thread-first "Hello"
  (list join " ")
  (list join "World")
  (list join "!"))      // "Hello World!"

Example: Multiple arguments

result = (thread-first 10
  (list add 5 15)       // (add 10 5 15) = 30
  (list multiply 2))    // (multiply 30 2) = 60

Example: Thread-last (value as LAST argument)

// Useful for non-commutative operations where value goes last
result = (thread-last 4
  (list divide 100)     // (divide 100 4) = 100 / 4 = 25
  (list power 2))       // (power 2 25) = 2^25

Thread-last use cases:

// Exponentiation: base ^ x
(thread-last 3 (list power 2))  // 2^3 = 8

// Division: numerator / x
(thread-last 5 (list divide 100))  // 100 / 5 = 20

// Comparison: value > x
(thread-last 50 (list greater_than 100))  // 100 > 50 = 1

✅ NEW: Thread-last now works with list operations!

Use collection-last wrappers: map-last, reduce-last, filter-last

// Thread-last with list processing
numbers = (list 1 2 3 4 5)

result = (thread-last numbers
  (list map-last {x i -> <- (multiply x 2)})
  (list filter-last {x i -> <- (greater_than x 5)})
  (list reduce-last {a x i -> <- (add a x)} 0))

(println result)  // 30 (6+8+10)

Collection Functions:

With thread-first: use map, reduce

With thread-last: use map-last, reduce-last, filter-last

Syntax: Forms must be lists: (list function args...) not (function args...)

String Module

Franz provides a comprehensive string manipulation library via the use function. Load stdlib/string.franz to access 10 essential string functions.

Loading the String Module:

(use "stdlib/string.franz" {
  // String functions available here
  result = (uppercase "hello")
  (println result)  // HELLO
})

Available Functions:

(uppercase s) - Convert string to uppercase
(lowercase s) - Convert string to lowercase
(trim s) - Remove leading and trailing whitespace
(split s delimiter) - Split string by delimiter into list
(replace s old new) - Replace all occurrences of substring
(repeat s count) - Repeat string N times
(starts_with s prefix) - Check if string starts with prefix (returns 1/0)
(ends_with s suffix) - Check if string ends with suffix (returns 1/0)
(contains s substr) - Check if string contains substring (returns 1/0)
(char_at s index) - Get character at index (0-based)

Example: Text Processing

(use "stdlib/string.franz" {
  input = "  Hello World  "

  // Clean and transform text
  cleaned = (trim input)                    // "Hello World"
  upper = (uppercase cleaned)               // "HELLO WORLD"
  replaced = (replace upper "WORLD" "FRANZ") // "HELLO FRANZ"

  (println replaced)

  // Check patterns
  (if (starts_with cleaned "Hello") {
    (println "Greeting detected!")
  } {})
})

Example: String Validation

(use "stdlib/string.franz" {
  url = "https://example.com"

  // Validate URL format
  is_https = (starts_with url "https://")
  has_domain = (contains url ".com")

  (if (and is_https has_domain) {
    (println "Valid HTTPS URL")
  } {
    (println "Invalid URL")
  })
})

Math Module

Franz provides a comprehensive mathematical library via the use function. Load stdlib/math.franz to access 15 mathematical functions and constants.

Loading the Math Module:

(use "stdlib/math.franz" {
  // Math functions available here
  result = (sqrt 16)
  area = (multiply PI (power 5 2))
  (println "Square root of 16:" result)
  (println "Circle area (r=5):" area)
})

Available Functions:

Constants: PI (3.14159...), E (2.71828...)
Basic Math: abs, sqrt, floor, ceil, round, max, min, clamp
Statistics: sum, average, median
Number Theory: factorial, gcd

Example: Statistical Analysis

(use "stdlib/math.franz" {
  scores = [85, 92, 78, 95, 88]

  (println "Total:" (sum scores))           // 438
  (println "Average:" (average scores))     // 87.6
  (println "Median:" (median scores))       // 88

  // Find min/max
  maximum = (reduce scores {acc item index -> <- (max acc item)} 0)
  minimum = (reduce scores {acc item index -> <- (min acc item)} 100)

  (println "Range:" minimum "to" maximum)   // 78 to 95
})

Example: Geometry Calculations

(use "stdlib/math.franz" {
  // Circle
  radius = 7
  circumference = (multiply 2 (multiply PI radius))
  area = (multiply PI (power radius 2))

  (println "Circumference:" circumference)  // 43.98...
  (println "Area:" area)                    // 153.93...

  // Distance between points
  distance = (sqrt (add (power 3 2) (power 4 2)))
  (println "Distance:" distance)            // 5.0
})

List Module

Franz provides advanced list operations beyond the built-in map, filter, and reduce functions. Load stdlib/list.franz to access 12 powerful list manipulation functions.

Loading the List Module:

(use "stdlib/list.franz" {
  // List functions available here
  numbers = [3, 1, 4, 1, 5, 9, 2, 6]
  sorted = (sort numbers)
  unique_sorted = (unique sorted)
  (println "Sorted:" sorted)
  (println "Unique:" unique_sorted)
})

Available Functions:

Transformation: reverse, unique, flatten, zip
Filtering: take, drop, partition
Inspection: any, all
Generation: filled, chunk, sort

Example: Data Processing Pipeline

(use "stdlib/list.franz" {
  data = (list 5 2 8 1 9 3 7 4 6)

  // Sort and get top 3
  sorted = (sort data)                // [1, 2, 3, 4, 5, 6, 7, 8, 9]
  top3 = (take (reverse sorted) 3)    // [9, 8, 7]

  (println "Top 3:" top3)
})

Example: Working with Predicates

(use "stdlib/list.franz" {
  numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]

  // Check predicates
  has_large = (any numbers {x i -> <- (greater_than x 5)})    // 1 (true)
  all_positive = (all numbers {x i -> <- (greater_than x 0)}) // 1 (true)

  // Partition by even/odd
  result = (partition numbers {x i -> <- (is (remainder x 2) 0)})
  evens = (get result 0)    // [2, 4, 6, 8, 10]
  odds = (get result 1)     // [1, 3, 5, 7, 9]

  (println "Evens:" evens)
  (println "Odds:" odds)
})

Example: Batch Processing

(use "stdlib/list.franz" {
  items = (range 10)              // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  batches = (chunk items 3)       // [[0,1,2], [3,4,5], [6,7,8], [9]]

  (println "Processing" (length batches) "batches...")
  (map batches {batch index ->
    (println "  Batch" index ":" batch)
    <- void
  })
})

I/O Module

The I/O Module (stdlib/io.franz) provides 8 essential file system utility functions for Franz programs. Status: ✅ COMPLETE (8/8 functions, 40+ tests passing).

Functions:

exists - Check if path exists (file or directory)
is_file - Check if path is a regular file
is_dir - Check if path is a directory
list_dir - List directory contents as a list
basename - Extract filename from path
dirname - Extract directory from path
join_path - Join path components with / separator (pure Franz!)
read_lines - Read file as list of lines

Quick Example:

(use "stdlib/io.franz" {
  // Check if file exists
  (if (exists "README.md") {
    (println "README exists!")
  })

  // List directory contents
  files = (list_dir "src")
  (println "Source files:" files)

  // Join path components
  path = (join_path (list "docs" "stdlib" "io.md"))
  (println "Full path:" path)

  // Extract filename and directory
  full_path = "src/main.c"
  dir = (dirname full_path)       // "src"
  file = (basename full_path)     // "main.c"
  (println "Directory:" dir "File:" file)

  // Read file line by line
  lines = (read_lines "README.md")
  line_count = (length lines)
  (println "README has" line_count "lines")
})

Common Patterns:

File Existence Check:

(if (exists "config.franz") {
  config = (use "config.franz")
} {
  (println "Config file not found")
})

Directory Traversal:

files = (list_dir "examples")
(map files {item index ->
  (println "Example" (add index 1) ":" item)
})

Path Construction:

components = (list "docs" "stdlib" "io.md")
full_path = (join_path components)
// Result: "docs/stdlib/io.md"

Path Decomposition:

path = "src/stdlib.c"
dir = (dirname path)         // "src"
file = (basename path)       // "stdlib.c"

Integration with List Module:

(use "stdlib/list.franz" {
(use "stdlib/io.franz" {
  files = (list_dir "src")
  c_files = (filter files {item index ->
    <- (ends_with item ".c")    // Using string module
  })
  sorted = (sort c_files)
  (println "Sorted C files:" sorted)
})
})

Edge Cases:

Empty inputs: exists("") → 0, list_dir("nonexistent") → [], join_path([]) → ""
Trailing slashes: basename("src/") → "src", join_path(["src/", "file.c"]) → "src/file.c"
Nested paths: dirname("a/b/c.txt") → "a/b", join_path(["a", "b", "c"]) → "a/b/c"

Implementation Highlights:

Shell integration for reliability: exists, is_file, is_dir, list_dir, basename, dirname use POSIX commands
Pure Franz implementation: join_path implemented using reduce (no shell overhead)
Cross-platform: Works on all Unix-like systems (Linux, macOS, BSD)

Performance:

Shell command functions: ~1-5ms overhead per call
Pure Franz functions: No shell overhead
Optimization tip: Cache exists checks when checking same path multiple times

Standard Library Complete 🎉

All 45 functions implemented and tested (100%):

Module	Functions	Status
stdlib/string.franz	17/17	✅ COMPLETE
stdlib/math.franz	8/8	✅ COMPLETE
stdlib/list.franz	12/12	✅ COMPLETE
stdlib/io.franz	8/8	✅ COMPLETE
TOTAL	45/45	✅ 100%

For complete module documentation and examples, see stdlib/README.md.

Development

To identify the current interpreter version, use the -v flag.

./franz -v

When debugging the interpreter, it may be useful to compile with the -g flag.

gcc src/*.c -g -Wall -lm -o franz

This will allow Valgrind to provide extra information,

valgrind --leak-check=full -s ./franz -d YOURCODE.franz

On mac, you can use leaks,

leaks -atExit -- ./franz YOURCODE.franz

To obtain debug information about how your code is interpreted (Tokens, AST, etc.), add the -d flag.

./franz -d YOURCODE.franz

You can also pipe code straight into franz (passed files always take priority over piped code).

echo '(print (add 1 2) "\\n")' | ./franz

Credit

Built by Mohammad Tanzil Idrisi

Name		Name	Last commit message	Last commit date
Latest commit History 18 Commits
benchmarks		benchmarks
docs		docs
examples		examples
scripts		scripts
src		src
stdlib		stdlib
test		test
.gitignore		.gitignore
Makefile		Makefile
Makefile.runtime		Makefile.runtime
README.md		README.md
build.rsp		build.rsp
franz-check		franz-check
run-comparison.sh		run-comparison.sh
test-println-if.franz		test-println-if.franz

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Franz — Functional, Prototype‑Oriented Programming Language

Lexical Scoping

Control Flow and Pattern Matching

If/When/Unless Statements

Cond Chains (Pattern Matching)

Type Guards

Build the interpreter (excludes franz-check tool)

Alternative: Include all source files

Debug build (for memory testing)

Run any example

Debug mode (shows tokens, AST, evaluation, scoping mode)

Check version

Use dynamic scoping (legacy mode)

Set scoping via environment variable

Getting Started

Install

Basics

Standard Library

IO

Comparisons

Logical Operators

Arithmetic

Control

Types

List and String

List Helpers (Recursive Programming)

Dictionary (Record) Functions

Function Composition

Partial Application

Threading Macros

String Module

Math Module

List Module

I/O Module

Standard Library Complete 🎉

Development

Credit

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