> ## Documentation Index
> Fetch the complete documentation index at: https://companyname-a7d5b98e-security-edits.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Fift deep dive

export const Image = ({src, darkSrc, alt = '', darkAlt, href, target, height = 342, width = 608, noZoom = false, center = false}) => {
  const isSVG = src.match(/\.svg(?:[#?].*?)?$/i) !== null;
  const shouldInvert = isSVG && !darkSrc;
  const shouldCreateLink = href !== undefined;
  const minPx = 9;
  const maxPx = 608;
  const expectedPx = `a number or a string with a number that is greater than ${minPx - 1} and less than or equal to ${maxPx}`;
  const createInvalidPropCallout = (title, received, expected) => {
    return <Danger>
        <span className="font-bold">
          Invalid <code>{title.toString()}</code> passed!
        </span>
        <br />
        <span className="font-bold">Received: </span>
        {received.toString()}
        <br />
        <span className="font-bold">Expected: </span>
        {expected.toString()}
        {}
      </Danger>;
  };
  const checkValidDimensionValue = value => {
    switch (typeof value) {
      case "string":
      case "number":
        const num = Number(value);
        return Number.isSafeInteger(num) && num >= minPx && num <= maxPx;
      default:
        return false;
    }
  };
  let callouts = [];
  if (height && !checkValidDimensionValue(height)) {
    callouts.push(createInvalidPropCallout("height", height, expectedPx));
  }
  if (width && !checkValidDimensionValue(width)) {
    callouts.push(createInvalidPropCallout("width", width, expectedPx));
  }
  if (callouts.length !== 0) {
    return callouts;
  }
  const heightPx = Number(height);
  const widthPx = Number(width);
  const shouldCenter = center === "true" || center === true ? true : false;
  const shouldNotZoom = noZoom === "true" || noZoom === true ? true : false;
  const images = <>
      <img className="block dark:hidden" src={src} alt={alt} {...height && ({
    height: heightPx
  })} {...width && ({
    width: widthPx
  })} {...(shouldCreateLink || shouldInvert || shouldNotZoom) && ({
    noZoom: "true"
  })} />
      <img className={`hidden dark:block ${shouldInvert ? "invert" : ""}`} src={darkSrc ?? src} alt={darkAlt ?? alt} {...height && ({
    height: heightPx
  })} {...width && ({
    width: widthPx
  })} {...(shouldCreateLink || shouldInvert || shouldNotZoom) && ({
    noZoom: "true"
  })} />
    </>;
  if (shouldCreateLink) {
    if (shouldCenter) {
      return <div style={{
        display: "flex",
        justifyContent: "center"
      }}>
          <a href={href} target={target ?? "_self"}>
            {images}
          </a>
        </div>;
    }
    return <a href={href} target={target ?? "_self"}>
        {images}
      </a>;
  }
  if (shouldCenter) {
    return <div style={{
      display: "flex",
      justifyContent: "center"
    }}>{images}</div>;
  }
  return images;
};

export const Aside = ({type = "note", title = "", icon = "", iconType = "regular", children}) => {
  const asideVariants = ["note", "tip", "caution", "danger"];
  const asideComponents = {
    note: {
      outerStyle: "border-sky-500/20 bg-sky-50/50 dark:border-sky-500/30 dark:bg-sky-500/10",
      innerStyle: "text-sky-900 dark:text-sky-200",
      calloutType: "note",
      icon: <svg width="14" height="14" viewBox="0 0 14 14" fill="currentColor" xmlns="http://www.w3.org/2000/svg" className="w-4 h-4 text-sky-500" aria-label="Note">
          <path fill-rule="evenodd" clip-rule="evenodd" d="M7 1.3C10.14 1.3 12.7 3.86 12.7 7C12.7 10.14 10.14 12.7 7 12.7C5.48908 12.6974 4.0408 12.096 2.97241 11.0276C1.90403 9.9592 1.30264 8.51092 1.3 7C1.3 3.86 3.86 1.3 7 1.3ZM7 0C3.14 0 0 3.14 0 7C0 10.86 3.14 14 7 14C10.86 14 14 10.86 14 7C14 3.14 10.86 0 7 0ZM8 3H6V8H8V3ZM8 9H6V11H8V9Z"></path>
        </svg>
    },
    tip: {
      outerStyle: "border-emerald-500/20 bg-emerald-50/50 dark:border-emerald-500/30 dark:bg-emerald-500/10",
      innerStyle: "text-emerald-900 dark:text-emerald-200",
      calloutType: "tip",
      icon: <svg width="11" height="14" viewBox="0 0 11 14" fill="currentColor" xmlns="http://www.w3.org/2000/svg" className="text-emerald-600 dark:text-emerald-400/80 w-3.5 h-auto" aria-label="Tip">
          <path d="M3.12794 12.4232C3.12794 12.5954 3.1776 12.7634 3.27244 12.907L3.74114 13.6095C3.88471 13.8248 4.21067 14 4.46964 14H6.15606C6.41415 14 6.74017 13.825 6.88373 13.6095L7.3508 12.9073C7.43114 12.7859 7.49705 12.569 7.49705 12.4232L7.50055 11.3513H3.12521L3.12794 12.4232ZM5.31288 0C2.52414 0.00875889 0.5 2.26889 0.5 4.78826C0.5 6.00188 0.949566 7.10829 1.69119 7.95492C2.14321 8.47011 2.84901 9.54727 3.11919 10.4557C3.12005 10.4625 3.12175 10.4698 3.12261 10.4771H7.50342C7.50427 10.4698 7.50598 10.463 7.50684 10.4557C7.77688 9.54727 8.48281 8.47011 8.93484 7.95492C9.67728 7.13181 10.1258 6.02703 10.1258 4.78826C10.1258 2.15486 7.9709 0.000106649 5.31288 0ZM7.94902 7.11267C7.52078 7.60079 6.99082 8.37878 6.6077 9.18794H4.02051C3.63739 8.37878 3.10743 7.60079 2.67947 7.11294C2.11997 6.47551 1.8126 5.63599 1.8126 4.78826C1.8126 3.09829 3.12794 1.31944 5.28827 1.3126C7.2435 1.3126 8.81315 2.88226 8.81315 4.78826C8.81315 5.63599 8.50688 6.47551 7.94902 7.11267ZM4.87534 2.18767C3.66939 2.18767 2.68767 3.16939 2.68767 4.37534C2.68767 4.61719 2.88336 4.81288 3.12521 4.81288C3.36705 4.81288 3.56274 4.61599 3.56274 4.37534C3.56274 3.6515 4.1515 3.06274 4.87534 3.06274C5.11719 3.06274 5.31288 2.86727 5.31288 2.62548C5.31288 2.38369 5.11599 2.18767 4.87534 2.18767Z"></path>
        </svg>
    },
    caution: {
      outerStyle: "border-amber-500/20 bg-amber-50/50 dark:border-amber-500/30 dark:bg-amber-500/10",
      innerStyle: "text-amber-900 dark:text-amber-200",
      calloutType: "warning",
      icon: <svg className="flex-none w-5 h-5 text-amber-400 dark:text-amber-300/80" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="2" aria-label="Warning">
          <path stroke-linecap="round" stroke-linejoin="round" d="M12 9v2m0 4h.01m-6.938 4h13.856c1.54 0 2.502-1.667 1.732-3L13.732 4c-.77-1.333-2.694-1.333-3.464 0L3.34 16c-.77 1.333.192 3 1.732 3z"></path>
        </svg>
    },
    danger: {
      outerStyle: "border-red-500/20 bg-red-50/50 dark:border-red-500/30 dark:bg-red-500/10",
      innerStyle: "text-red-900 dark:text-red-200",
      calloutType: "danger",
      icon: <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" fill="currentColor" className="text-red-600 dark:text-red-400/80 w-4 h-4" aria-label="Danger">
          <path d="M17.1 292c-12.9-22.3-12.9-49.7 0-72L105.4 67.1c12.9-22.3 36.6-36 62.4-36l176.6 0c25.7 0 49.5 13.7 62.4 36L494.9 220c12.9 22.3 12.9 49.7 0 72L406.6 444.9c-12.9 22.3-36.6 36-62.4 36l-176.6 0c-25.7 0-49.5-13.7-62.4-36L17.1 292zm41.6-48c-4.3 7.4-4.3 16.6 0 24l88.3 152.9c4.3 7.4 12.2 12 20.8 12l176.6 0c8.6 0 16.5-4.6 20.8-12L453.4 268c4.3-7.4 4.3-16.6 0-24L365.1 91.1c-4.3-7.4-12.2-12-20.8-12l-176.6 0c-8.6 0-16.5 4.6-20.8 12L58.6 244zM256 128c13.3 0 24 10.7 24 24l0 112c0 13.3-10.7 24-24 24s-24-10.7-24-24l0-112c0-13.3 10.7-24 24-24zM224 352a32 32 0 1 1 64 0 32 32 0 1 1 -64 0z"></path>
        </svg>
    }
  };
  let variant = type;
  let gotInvalidVariant = false;
  if (!asideVariants.includes(type)) {
    gotInvalidVariant = true;
    variant = "danger";
  }
  const iconVariants = ["regular", "solid", "light", "thin", "sharp-solid", "duotone", "brands"];
  if (!iconVariants.includes(iconType)) {
    iconType = "regular";
  }
  return <>
      <div className={`callout my-4 px-5 py-4 overflow-hidden rounded-2xl flex gap-3 border ${asideComponents[variant].outerStyle}`} data-callout-type={asideComponents[variant].calloutType}>
        <div className="mt-0.5 w-4" data-component-part="callout-icon">
          {}
          {icon === "" ? asideComponents[variant].icon : <Icon icon={icon} iconType={iconType} size={14} />}
        </div>
        <div className={`text-sm prose min-w-0 w-full ${asideComponents[variant].innerStyle}`} data-component-part="callout-content">
          {gotInvalidVariant ? <p>
              <span className="font-bold">
                Invalid <code>type</code> passed!
              </span>
              <br />
              <span className="font-bold">Received: </span>
              {type}
              <br />
              <span className="font-bold">Expected one of: </span>
              {asideVariants.join(", ")}
            </p> : <>
              {title && <p className="font-bold">{title}</p>}
              {children}
            </>}
        </div>
      </div>
    </>;
};

<Aside type="note">
  The official smart contract language of TON Blockchain is [Tolk](/tolk/overview). Fift is now a **legacy** language, with its compiler no longer maintained.

  Fift pages will be moved down in the sidebar in mid-April 2026. Here is the preview of a possible future placement, right between "Blockchain foundations" and "Contribute" sections:

  <Image src="/resources/images/tmp-func-fift-light.png" darkSrc="/resources/images/tmp-func-fift-dark.png" alt="Preview of a possible future placement of FunC and Fift languages in the sidebar." width={294} height={190} noZoom={true} />
</Aside>

Fift is a high-level stack-based language used for local manipulation of cells and other TVM primitives. Its primary purpose is to compile TVM assembly code into contract code as a bag-of-cells (BoC).

<Aside type="caution">
  **Advanced topic notice** This section covers low-level interactions with TON's implementation details. Before proceeding, ensure you have:

  * Solid experience with stack-based programming paradigms
  * Understanding of virtual machine architectures
  * Familiarity with low-level data structures
</Aside>

## Simple arithmetic

Use the Fift interpreter as a calculator with reverse Polish notation:

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
6 17 17 * * 289 + .
2023 ok
```

This example calculates:

1. `17 * 17 = 289`
2. `6 * 289 = 1734`
3. `1734 + 289 = 2023`

## Standard output

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
27 emit ."[30;1mgrey text" 27 emit ."[37m"
grey text ok
```

* `emit` prints the Unicode character corresponding to the number on top of the stack
* `."..."` outputs a constant string

## Defining functions (Fift words)

To define a word, follow these steps:

1. **Enclose the word's effects** in curly braces `{}`.
2. **Add a colon `:`** after the closing brace.
3. **Specify the word's name** after the colon.

The first line defines the word `increment` as a function that increases `x` by `1`.

**Examples:**

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
// Fift.fif
{ x 1 + } : increment
{ minmax drop } : min
{ minmax nip } : max
```

In TON, multiple **defining words** exist, not just `:`. They differ in behavior:

* **Active words** – Operate inside curly braces `{}`.
* **Prefix words** – Do not require a trailing space.

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
// Fift.fif
{ bl word 1 2 ' (create) } "::" 1 (create)
{ bl word 0 2 ' (create) } :: :
{ bl word 2 2 ' (create) } :: :_
{ bl word 3 2 ' (create) } :: ::_
{ bl word 0 (create) } : create
```

## Conditional execution

Execute code blocks conditionally using `cond`:

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
{ { ."true " } { ."false " } cond } : ?.   4 5 = ?.  4 5 < ?.
false true  ok
{ ."hello " } execute ."world"
hello world ok
```

## Loops

Use loop primitives for repetitive operations:

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
// GetOpt.fif
// ( l c -- l') Removes first c elements from list l
{ ' safe-cdr swap times } : list-delete-first
```

Loop word `times` takes two arguments - let's call them `cont` and `n` - and executes `cont` `n` times.
Here `list-delete-first` takes continuation of `safe-cdr` (command deleting head from Lisp-style list), places it under `c`, and then `c` times removes head from list present on stack.
`while`/`until` provide conditional looping.

## Comments

Comments in Fift are defined in `Fift.fif` and come in two forms:

1. **Single-line comments**: Start with `//` and continue to the end of the line
2. **Multiline comments**: Start with `/*` and end with `*/`

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
// Fift.fif
{ 0 word drop 0 'nop } :: //
{ char " word 1 { swap { abort } if drop } } ::_ abort"
{ { bl word dup "" $= abort"comment extends after end of file" "*/" $= } until 0 'nop } :: /*
```

#### How comments work

Fift programs are sequences of words that transform the stack or define new words. Comments must work even during word definitions, requiring them to be **active words** (defined with `::`).

Breaking down the `//` definition:

1. `0` - Pushes zero onto the stack
2. `word` - Reads characters until reaching one matching the top stack value (zero is special - skips leading spaces then reads to end of line)
3. `drop` - Removes the comment text from the stack
4. `0` - Pushes zero again (number of results for `::` definition)
5. `'nop` - Pushes an execution token that does nothing (equivalent to `{ nop }`)

## Using Fift for defining TVM assembly codes

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
// Asm.fif (line order reversed)
x{00} @Defop NOP
{ 1 ' @addop does create } : @Defop
{ tuck sbitrefs @ensurebitrefs swap s, } : @addop
{ @havebitrefs ' @| ifnot } : @ensurebitrefs
{ 2 pick brembitrefs 1- 2x<= } : @havebitrefs
{ rot >= -rot <= and } : 2x<=
...
```

### How `@Defop` works

`@Defop` checks available space for the opcode using `@havebitrefs`. If space is insufficient, it writes to another builder via `@|` (implicit jump).

**Important:** Always use `x{A988} @addop` instead of `x{A988} s,` to avoid compilation failures when space is limited.

### Including cells in contracts

You can embed large bag-of-cells into contracts:

```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
<b 8 4 u, 8 4 u, "fift/blob.boc" file>B B>boc ref, b> <s @Defop LDBLOB
```

This defines an opcode that:

1. Writes `x{88}` (`PUSHREF`) when included in the program
2. Adds a reference to the specified bag-of-cells
3. Pushes the cell to the TVM stack when executing `LDBLOB`

## Special features

### Ed25519 cryptography

Fift provides built-in support for Ed25519 cryptographic operations:

* **`newkeypair`** - Generates a private-public key pair
* **`priv>pub`** - Derives a public key from a private key
* **`ed25519_sign[_uint]`** - Creates a signature for given data using a private key
* **`ed25519_chksign`** - Verifies an Ed25519 signature

### TVM interaction

* **`runvmcode` and similar commands** - Executes TVM with a code slice taken from the stack

### File operations

* **Save BoC to file**:

  ```fift theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
  boc>B ".../contract.boc" B>file
  ```

## Continue learning

* [Fift: A Brief Introduction](/resources/pdfs/fiftbase.pdf) - *Nikolai Durov*