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Cairo Learning

Cairo lang learning notes

Environment

Setting up python environment:

python -m venv ~/cairo_venv
source ~/cairo_venv/bin/activate

Compiling:

cairo-compile app.cairo --output app_compiled.json

Running:

cairo-run --program=app_compiled.json --print_output --print_info --relocate_prints --print_memory

Format:

cairo-format -i app.cairo

Examples

There's a make helper for running examples in repo, e.g. running fib.cairo:

make run name=fib

Notes

• parentheses in return statements are required
• return statement is required to return values
• must always have return statement even if no return values
• function return statements need to be in parentheses and indicate how many values are returned
• cannot call functions are part of expressions (i.e. foo(bar()) will not work)
• cannot call functions in a loop
• cairo memory is immutable
• if values were previously set then assert statement is invoked, otherwise it sets the value
• the deference operator is [arr] (in brackets), it returns the value at memory address arr
• the output builtin passes beginning of memory segment to main
• convention is to return the next output cell to last one of output cell, e.g. output_ptr + 2 if output_ptr + 1 set
• by default variables are type field element felt
• a field element is integer in range P/2 < x < P/2 where P is a very large (prime) number (252-bit number) with 76 decimal digits.
• const SIZE has special meaning in some cases
• there is no < operator (use builtins)
• use assert_nn_le(x, y) to check 0 <= x <= y
• use alloc_locals as first statement is function to allow local variables throughout function
• use local to declare local variables and set alloc_locals at top of function
• use tempvar to allocate one memory cell for immediate use
• use let to define a reference; the expression is an alias and is not executed let x = y * y will not be invoked unlike tempvar x = y * y which stores the result)
• ap allocation pointer - points to an unused memory cell
• fp'frame pointer - points to frame of the current function.
• pc program counter - points to the current instruction
• %[ <pythone-code> %] evaluates python code, e.g. const value = %[ 2 * 3 %] + 100
• ... will cancel the arguments check and use args from stack instead, i.e. bar(); foo(..., y=5) where bar returns 4
• a hint is a block of python code that will be executed by provder before the next instruction
• hints are visible to the prover
• access secret inputs in hint with program_input['secret']
• a segment is a continuous chunk of memory
• cairo programs are kept in memory called the program segment
• the pc program counter starts at the beginning of program segment
• cairo programs have an execution segment where registers ap' and fp start
• memory cells; e.g. arr points to first memory cell of array, arr + 1 points to second memory cell, and so on

License

MIT