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Jeffrey Wilcke edited this page Jun 6, 2014 · 16 revisions

Compiler & Language definition for the Ethereum project

Mutan is a C-Like language for the Ethereum project. Mutan supports a full, dynamic higher level language that compiles to native Ethereum Assembler. Repo will be moved.

An online editor and compiler can be found here

Installation

go get -u github.com/obscuren/mutan/mutan

Notation

The syntax is specified using Extended Backus-Naur Form (EBNF):

digit excluding zero = "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
digit                = "0" | digit excluding zero ;

Keywords

The following keywords are reserved and may not be used as identifiers

this if else return exit for asm nil transact create call sizeof true false

Operators and delimiters

Mutan contains the following operators and delimiters

+       **       =       |       (     )
-       ^        ==      &       {     }
*       >=       ++      ;       <<    >>
/       <=       --      !       :=

Numeric types

Numeric types in Mutan can only be represented by integer values and are architecture-independent. They are all represented in big endian byte order. Numbers may be specified in decimal and hexadecimal format.

10      0xabc     0xABC

Arrays

Arrays are of theoretical unlimited length

ArrayType   = Var "[" Number "]" .

The following is a valid array:

var[10] a

Declarations

A declaration binds an identifier to a type. Every identifier must be declared. No identifier may be declared twice and all variables are scoped to the current executing frame (function).

Declaration = TypeDecl .

A declaration can be done in several ways. First and foremost every identifier must be declared either with a type or a variant. Variants can be created in two separate ways, either with the var keyword or by using the := assignment operator.

var a = "a"
c := "c"

Statements

Statement = Declaration | Block | IfStmt | ForStmt | Expression | Lambda

Expression

Expression = Ptr | Number | Hex | String | Identifier .
Ptr        = Identifier | "nil" .
Number     = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
Hex        = "0x" "a" | "b" | "c" | "d" | "e" | "f" | Number .
String     = """ * """
Identifier = * .

Blocks

Blocks contain, but not necessarily, contain lists of Statements within matching brackets.

Block         = "{" StatementList "}" .
StatementList = { Statement ";" } .

If statements

If statements specify the conditional execution of two branches according to the value of an expression. If the expression evaluated to true, the "if" branch is executed, else, if present, the else branch is executed.

IfStmt = "if" [ SimpleStmt ";" ] Expression Block [ "else" Block ] .
if x < 10 {
   x = maximum
}

The expression may be preceded by a simple statement which executes before the boolean expression

if x := this.Value(); x < 10 {
    x = maximum
} else {
    y = 10
}

For statement

A "for" statements specifies repeated execution of a block, the iteration is controlled by a conditional block.

ForStmt  = "for" [ InitStmt ] ";" [ Condition ] ";" [ PostStmt ] .
InitStmt = SimpleStmt .
PostStmt = SimpleStmt .

A "for" in it's simplest form is a C-Like "while" statement (therefor Mutan doesn't have a "while")

for a < b {
    a = a * 2
}

A "for" statement in it's purest form is controlled my a initialiser, condition and a post statement which will be executed at the end of the Block

for var a = 0; a < b; a++ {
    b = b - 1
}
for cond { T() }         is the same as    for ; cond ; { T() }
for cond; post { T() }   is the same as    for ; cond; post { T() }

String literal

String literals are supported by enclosing a line of text with matching quotes "string". Strings can be assigned to variables and stored in memory. Strings have a limitation in size. Strings can be no longer than 32 bytes. Attempting to create a string larger than 32 bytes will result in a compile error. This is due to the limitation of the size that is allowed to be stored in each storage location.

str := "hello world"
this.store[0] = "hello world"

Function Declarations

A function declarations binds an identifier, the function name, to a function.

FunctionDecl  = "func" FunctionName Signature .
Signature     = Parameters [ Result ] .
Parameters    = "(" [ ParameterList [ "," ] ] ")" .
ParameterList = ParemeterDecl { "," ParameterDecl } .
ParameterDecl = [ Var Identifier ] .

If the function's signature declares a result parameter, the function body's statement list must end with a return statement (TODO).

func fib(var n) var {
    if n == 0 {
        return 0
    } else {
        if n == 1 {
            return 1
        }
    }

    return fib(n-1) + fib(n-2)
}

Lambda

A lambda in mutan is a semi lambda and, at the time of writing, can only be used in a return statement. A lambda will compile the given code, enclosed by brackets { // code }. Lambdas are allowed to be of arbitrary size and take up as much memory as needed.

a := "hello"

return lambda {
     a := 20
     if a == 20 {
     }
}

Lambdas have their own scope and do not share any memory outside of their own scope, neither can they use any memory outside of their scope. Lambdas should be viewed as separate instances of code.

var a = "hello"
return lambda {
    b := a // Undefined references error
}

Build in functions

Mutan comes with a couple build in functions for stopping, creating and transacting between multiple objects and context functions.

exit()
"exit()"

Stops the execution of the current call

call(addr, value, gas, in, out)
Success = "call(" Expression, Expression, Expression, Ptr, Ptr ")"

Calls contract specified by the address and executes. Arguments can be passed to the in argument and the return value can be specified by the out parameters. Return a 1 or 0 depending whether this call was success or not.

transact(addr, value, data)
Success = "transact(" Expression, Expression, Ptr ")"

Handles a transaction between two objects.

create(value, script)
Address = "create(" Expression, Expression ")"

Creates a new contract given by script and returns the Address of the transaction.

Context functions

The following functions relate to the current executing context (i.e. the closure). These build-in functions are prefixed with this..

Method     = "this" Dot MethodName "(" [ Expression ] ")" .
Dot        = "." .
MethodName = "dataLoad" | "dataSize" | "origin" | "address" | "caller" | "gasPrice" | "value" |
             "diff" | "prevHash" | "time" | "gasPrice" | "number" | "coinbase" | "gas" .
data          Returns the x'th value of the attached data of this call
dataSize      Returns the size of the data attached to this call
origin        Returns the original caller that initiated the first call
address       Returns the direct address of this execution
caller        Returns the current caller of the closure
gasPrice      Returns the gas price attached to this call
value         Returns the value attached to this call
balance       Returns the value of the current call
diff          Returns the current difficulty
prevHash      Returns the previous block's hash
time          Returns the current block's timestamp
gasPrice      Returns the attached call's gas price
number        Returns the current block's number
coinbase      Returns the current block's coinbase
gas           Returns the current call's attached amount of gas

Assembler

Inline assembler is allowed through the asm keyword

InlineAssembler = "asm" "(" Code ")" .
Code            = "abcdefghijklmnopqrstuwvxyz" | "1234567890" .

Pre processor

Mutan has a very basic pre processor that takes any #define and replaces that throughout the source code

Output = "#define" Word [ Expression ] .

Basic syntax

#define ADDR 0xe6716f9544a56c530d868e4bfbacb172315bdead

func pow(var x, var y) {
    return x ** y
}

p := pow(10, 2)

var a = 20
var b = 10

var str = "hello"
otherStr := "world"

if a < b {
    exit()
} else {
    // :-)
    if !a {
        if this.data[0] ** 10 >= 10 {
            this.data[0] = 1000;
        }
    }
}

this.store[a] = 10000
this.store[b] = this.origin()

for i := 0; i < 10; i++ {
    int32[10] out
    call(0xaabbccddeeff112233445566, 0, 10000, i, out)
}

// tx without input data
transact(0xa78f6abe, 10000, nil)
// no args and return values
call(0xab, 0, 10000, nil, nil)
// create contract
big ret = create(value, 0xaabbccddeeff0099887766552211)

var left = 8 << 2
left = left >> 2

asm (
    PUSH 10
    PUSH 0
    MSTORE
)

return lambda {
    this.store[0] = "hello"
}
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