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Ceu
Ceu is a synchronous reactive language that aims to offer a higher-level and safer alternative to C/C++. Ceu reconciles Structured Concurrency with Reactive Programming, extending classical structured programming with two main functionalities:
- Concurrency:
- A set of structured mechanisms to compose concurrent lines of execution
(e.g.,
spawn,paror,pauseon).
- A set of structured mechanisms to compose concurrent lines of execution
(e.g.,
- Event Handling:
- An
awaitstatement to suspend a line of execution and wait for events. - An
emitstatement to broadcast events and awake awaiting lines of execution.
- An
Ceu also provides algebraic data types with subtyping and inheritance, (TODO: parametric polymorphism), local type inference, and region-based memory management. The goal of regions is to provide safe memory management for dynamically allocated data structures.
Ceu compiles to C and integrates seamlessly with it at the source level.
C identifiers can be accessed with the _ prefix.
Conversely, Ceu types and identifiers can also be accessed from C.
In summary, Ceu provides structured-reactive concurrency, region-based memory management, and source-level integration with C.
Ceu is free software.
INSTALL & RUN
$ sudo make install
$ ceu idea/src/input-output.ceu
... (type 10) ...
10
EXAMPLES
TODO
MANUAL
1. STATEMENTS
Block
A block delimits the scope of variables between curly braces:
{
var x: ()
... x ... -- `x` is visible here
}
... x ... -- `x` is not visible here
A block may contain an uppercase label to identify its memory region:
{ @MYBLOCK -- `@MYBLOCK` can be referenced in allocations
...
}
The label @GLOBAL corresponds to the outermost block of the program.
The label @LOCAL corresponds to the current block.
Variable Declaration
A declaration introduces an identifier as a variable of the given type in the current block:
var x: () -- `x` is of unit type `()`
var y: _int -- `y` is a native `int`
var z: [_int,_int] -- `z` is a tuple of ints
A declaration may include an assignment, which may infer the type of the variable:
var x = () -- `x` holds `()` of type `()`
var x: () = () -- equivalent to above
Assignment
An assignment changes the value of a variable, native identifier, tuple or union discriminator, or pointer dereference:
set x = () -- sets `x` to the unit value `()`
set _n = _1 -- sets native `_n` to hold native `_1`
set tup.1 = n -- changes the tuple index value
set ptr\ = v -- dereferences pointer `ptr` and assigns `v`
The value to be assigned can be any expression or statement that yields a value (input, spawn, await, new).
Call
A call invokes an expression:
call f _0 -- calls `f` passing `_0`
Input & Output
Input and output statements communicate with external I/O devices. They receive a named constructor corresponding to the device and parameters to communicate:
output Std [_0,_0] -- outputs "[0,0]" to stdio
var x = input Std (): _int -- reads an `_int` from stdio
An input evaluates to a value of the required explicit type.
The special device Std works for the standard input & output device and
accepts any value as argument.
TODO: input std should only accept :_(char*)
TODO: input/output hierarchy
C declarations for the I/O devices must prefix their identifiers with
input_ or output_:
void output_xxx: (XXX v) {
...
}
Sequence
A sequence of statements separated by blanks or semicolons ; execute one
after the other:
var x: _int -- first declares `x`
set x = input std (): _int -- then assigns `_int` input to `x`
output std x -- finally outputs `x`
Conditional
An if tests an _int value and executes one of the true or false
branches depending on the result:
if x {
-- true branch
call f () -- calls `f` if `x` is nonzero
} else {
-- false branch
call g () -- calls `g` otherwise
}
Repetition
A loop executes a block of statements indefinitely until it reaches a break
statement:
loop {
... -- repeats this command indefinitely
if ... { -- until this condition is met
break -- escapes the loop
}
}
Native
A native statement executes a block of code in the host language C:
native _{
printf("Hello World!");
}
Function
A function declaration abstracts a block of statements that can be invoked with
arguments.
The argument can be accessed through the identifier arg.
The result can be assigned to the identifier ret.
The return statement exits a function::
set f = func () -> () {
set ret = arg -- assigns arg to the result
return -- exits function
}
Function declarations are further documented as expressions, since they are
actually func expressions assigned to variables.
2. TYPES
Unit
The unit type () represents absence of information and has only the single
unit value ().
Native
A native type holds external values from C, i.e., values which Ce does
not create or manipulate directly.
A native type identifier always starts with an underscore _:
_char _int _{FILE*}
Pointer
A pointer type holds a pointer to another value and can be applied to
any other type with the prefix slash /.
A pointer must also specify the block in which its pointed data is held:
/_int @LOCAL -- a pointer to an `_int` held in then current block
/[_int,()] @S -- a pointer to a tuple held in block `@S`
Tuple
A tuple type holds a value for each of its subtypes.
A tuple type identifier is a comma-separated list of types enclosed with
brackets [ and ]:
[(),(),()) -- a triple of unit types
[(),[_int,()]] -- a pair containing another pair
Union
A union type holds a value of one of its subtypes.
A tuple type identifier is a comma-separated list of types enclosed with
angle brackets < and >:
<(),(),()> -- a union of three unit types
<(),[_int,()]> -- a union of unit and a pair
Recursive Union Pointer
A recursive union is a pointer with a caret subtype pointing upwards:
/<[_int, /^@S]>@S -- a linked list of `_int` held at block `@S`
The pointer caret /^ indicates recursion and refers to the enclosing
recursive union type.
Multiple n carets, e.g. /^^, refer to the n outer enclosing recursive
union pointer type.
The pointer caret can be expanded resulting in equivalent types:
/<[_int, /^@S]>@S -- a linked list of `_int`
/<[_int, /<[_int,/^@S]>@S>@S -- a linked list of `_int` expanded
Function
TODO: closure, blocks scopes
!--
- closures cannot modify original up (it is a stack variable that gets lost)
->
A function type holds a function value and is composed of the prefix func
and input and output types separated by an arrow ->:
func () -> _int -- input is unit and output is `_int`
func [_int,_int] -> () -- input is a pair of `_int` and output is unit
Special Types
Error
Event
Input & Output
3. EXPRESSIONS
Unit
The unit value is the single value of the unit type:
()
Variable
A variable holds a value of its type:
var x: _int
set x = _10 -- variable `x` holds native `_10`
output std x
Native
A native expression holds a value from C.
The expression must specify its type with a colon : sufix:
_(2+2): _int -- _(2+2) has type _int
_{f(x,y)}: _(char*) -- f returns a C string
Symbols defined in Ce can also be accessed inside native expressions:
var x: _int
set x = _10
output std _(x + 10) -- outputs 20
Pointer Upref & Dnref
A pointer points to a variable holding a value.
An upref (up reference or reference) acquires a pointer to a variable
with the prefix slash /.
A dnref (down reference or dereference) recovers a pointed value
given a pointer with the sufix backslash \:
var x: _int
var y: /_int@LOCAL
set y = /x -- acquires a pointer to `x`
output std y\ -- recovers the value of `x`
Tuple: Constructor and Discriminator
Constructor
A tuple holds a fixed number of values:
[(),_10] -- a pair with `()` and native `_10`
[x,(),y] -- a triple
Discriminator
A tuple discriminator suffixes a tuple with a dot . and an numeric
index to evaluate the value at the given position:
var tup: [(),_int]
set tup = [(),_10]
output std tup.2 -- outputs `10`
Union: Constructor, Allocation, Discriminator & Predicate
Constructor
A union constructor creates a value of a union type given a subcase index,
an argument, followed by a colon : with the explicit complete union type:
<.1 ()>: <(),()> -- subcase `.1` of `<(),()>` holds unit
<.2 [_10,_0]: <(),[_int,_int]> -- subcase `.2` holds a tuple
Null Pointer Constructor
A recursive union always includes a null pointer constructor <.0> that
represents data termination.
The null constructor must also include a colon sufix : with the explicit
complete union type:
var x: /<[_int,/^@S]>@S -- a linked list of `_int`
set x = <.0>: /<[_int,/^@S]>@S -- an empty linked list
Allocation
A recursive union constructor uses the new operation for dynamic allocation.
It returns a pointer of the type as result of the allocation.
It receives a constructor of the plain type sufixed by a colon : with the
block to allocate the data:
var z: /</^@S>@S
set z = <.0>: /</^@S>@S -- null
var x: /</^@S>@S
set x = new (<.1 z>:</^@S>): @S -- () -> null, allocated in block `@S`
Discriminator
A union discriminator suffixes a union with an exclamation ! and a
numeric index to access the value as one of its subcases:
var x: <(),_int>
... x!1 -- yields ()
var y: /<[_int,/^@S]>@S
... x\!1.1 -- yields an `_int`
... x\!1.2\!0 -- yields ()
If the discriminated subcase does not match the actual value, the attempted access raises a runtime error.
Predicate
A union predicate suffixes a union with a question ? and a
numeric index to check if the value is of the given subcase:
var x: <(),_int>
... x?1 -- checks if `x` is subcase `1`
var y: /<[_int,/^@S]>@S
... x\?1 -- checks if list is not empty
The result of a predicate is an _int value (_1 if success, _0 otherwise)
to be compatible with conditional statements.
Call
A call invokes a function with the given argument:
call f () -- f receives unit ()
call (id) x -- id receives variable x
call add [x,y] -- add receives tuple [x,y]
Calls may also specify blocks for pointer input and output:
call f @[@S] ptr: @LOCAL -- calls `f` passing `ptr` at `@S` and return at `@LOCAL`
Pointer inputs go in between brackets @[ and ] before the argument.
Pointer output goes after a colon : suffix after the argument.
Calls are further documented with functions.
Function
TODO
4. LEXICAL RULES
Comment
A comment starts with a double hyphen -- and ignores everything
until the end of the line:
-- this is a single line comment
Keywords and Symbols
The following keywords are reserved:
break -- escape loop statement
call -- function invocation
else -- conditional statement
func -- function type
if -- conditional statement
input -- input invocation
loop -- loop statement
native -- native statement
new -- allocation operation
output -- output invocation
return -- function return
set -- assignment statement
var -- variable declaration
The following symbols are valid:
{ } -- block delimeter, block labels
( ) -- unit type, unit value, group type & expression
[ ] -- tuple delimiter
< > -- union delimiter
; -- sequence separator
: -- type and block specification
-> -- function type signature
= -- variable assignment
/ -- pointer type, upref operation
\ -- dnref operation
, -- tuple & union separator
. -- tuple discriminator, union constructor
! -- union discriminator
? -- union predicate
^ -- recursive union
@ -- block labels
Variable Identifier
A variable identifier starts with a lowercase letter and might contain letters, digits, and underscores:
i myCounter x_10 -- variable identifiers
Block Label
A constant block label starts with at @ and contains only uppercase letters.
A parameter block label starts with at @ and contains only lowercase letters
with an option numeric suffix:
@GLOBAL @MYBLOCK @a @a1
Number
A number is a sequence of digits:
0 20
Numbers are used in tuple & union discriminators.
Native Token
A native token starts with an underscore _ and might contain letters,
digits, and underscores:
_char _printf _100 -- native identifiers
A native token may also be enclosed with curly braces { and } or
parenthesis ( and ).
In this case, a native token can contain any other characters:
_(1 + 1) _{2 * (1+1)}
SYNTAX
TODO: fields
Stmt ::= { Stmt [`;´ | `\n´] } -- sequence call f() ; call g()
| `{´ SCOPE Stmt `}´ -- block { @A ... }
// variables
| `var´ VAR [`:´ Type] [`=´ (Expr | EStmt)] -- variable declaration var x: _int = f ()
| `set´ Expr `=´ (Expr | EStmt) -- assignment set x = _10
EStmt ::= (`input` | `spawn` | `await` | `new`) ...
// invocations
| `output´ Expr -- data output output Std x
| `input´ Expr [`:´ Type] -- data input input Std (): _int
| `native´ [`type´] NAT -- native statement native _{ printf("hi"); }
| `call´ Expr -- call call f ()
// control flow
| `if´ Expr Block [`else´ Block] -- conditional if cnd { ... } else { ... }
| `loop´ Block -- loop loop { ... }
| `loop´ Expr `in´ Expr Block -- loop tasks loop tsk in tsks { ... }
| `throw´ Expr -- throw exception throw Error.Escape v
| `catch´ Expr Block -- catch exception catch Error?Escape { ... }
| `return´ [Expr] -- function return return v
| `break´ -- loop break break
// tasks
| `spawn´ Expr [`in´ Expr] -- spawn task spawn t () in ts
| `pause´ Expr -- pause task pause t
| `resume´ Expr -- resume task resume t
// events
| `emit´ [SCOPE | Expr] Expr -- emit event emit @A Event.Timer v
| `await´ Event -- await event await Event?Timer
// types
| `type´ TYPE [Pars] [Scps] [`=´ | `+=´] Type -- type declaration type Bool = <True=(),False=()>
// derived statements
| `func´ VAR `:´ Type Block Expr -- function declaration func f: ()->() { ... }
| `task´ VAR `:´ Type Block Expr -- task declaration task t: ()->()->() { ... }
| `ifs´ `{´ { Expr Block } [`else´ Block] `}´ -- conditionals ifs { cnd1 {} `\n´ cnd2 {} `\n´ else {} }
| `spawn´ Block -- task block spawn { ... }
| `defer´ Block -- task declaration defer { ... }
| `await´ TIMER -- await timer await 10s
| `await´ `spawn´ Expr -- await spawned task await spawn t
| `every´ [Expr | TIMER] Block -- every block every cnd { ... }
| `pauseon´ Expr Block -- pause block pauseon cnd { ... }
| `par´ Block { `with´ Block } -- parallel block par { ... } with { ... }
| `parand´ Block { `with´ Block } -- parallel and block parand { ... } with { ... }
| `paror´ Block { `with´ Block } -- parallel or block paror { ... } with { ... }
| `watching´ [Expr | TIMER] Block -- watching or block watching 500ms { ... }
Expr ::= `(´ Expr `)´ -- group (x)
| `(´ `)´ -- unit ()
| VAR -- variable i
| NAT [`:´ Type] -- native expression v: _int
| Null [`:´ Type] -- Null constructor Null: /List
| [`active´] TYPE [Expr] -- named constructor Bool.True Point [_10,_10] active Task ()
| `[´ [VAR `=´] Expr {`,´ [VAR `=´] Expr} `]´ -- tuple constructor [x,()] [x=_10,y=_20]
| `<´ `.´ (NUM | TYPE) [Expr] `>´ [`:´ Type] -- union constructor <.1 ()>: <(),()> <.True>
| `new´ Expr [`:´ SCOPE] -- union allocation new List.Cons: @LOCAL
| `if´ Expr `{´ Expr `}´ `else´ `{´ Expr `}´ -- if expression if cnd { ... } else { ... }
| [`func´ | `task´] Type Block -- function expression func ()->() { ... }
| Expr [Params] [Scopes] Expr [`:´ SCOPE] -- function call f ${_int} @[S] x: @LOCAL
| `/´ Expr -- upref /x
| Expr `\´ -- dnref x\
| Expr `::´ Type -- cast x::_long x::Super.Sub
| Expr `~´ -- unpack x~
| Expr `.´ [NUM | VAR] -- tuple discriminator x.1 pt.x
| Expr `!´ [NUM | TYPE] -- union discriminator x!1 x!Cons
| Expr `?´ [NUM | TYPE | `Null´] -- union predicate x?2 x?Null
// derived expressions
| TYPE Block -- function expression Func { ... }
| `ifs´ `{´ {Expr `{´ Expr `}´} [`else´ `{´ Expr `}´] `}´ -- conditionals ifs { cnd1 {e1} `\n´ cnd2 {e2} `\n´ else {e3} }
Type ::= `(´ Type `)´ -- group (func ()->())
| `(´ `)´ -- unit ()
| NAT -- native type _char
| PARAM -- parameter type $a1 $X
| `/´ Type [SCOPE] -- pointer /_int@S
| TYPE { `.´ (NUM | TYPE) } [Params] [Scopes] -- named type Bool Bool.1 Bool.False
| `[´ [VAR `:´] Type {`,´ [VAR `:´] Type} `]´ -- tuple [(),()] [x:_int,y:_int]
| `<´ [TYPE `=´] Type {`,´ [TYPE `=´] Type} `>´ -- union </List> <False=(),True=()>
| [`func´ | `task´] [[Params] [Scopes] `->´] Type [`->´ Type] `->´ Type -- function func f : ()->() { return () }
| Type.Tuple `+´ Type.Union -- type inheritance [...] + <...>
Params ::= `${´ [TYPE {`,´ TYPE}] `}´ -- list of type parameters ${a,b}
Scopes ::= `@{´ [SCOPE {`,´ SCOPE}] `}´ -- list of scopes @{LOCAL,a1}
PARAM ::= $[A-Za-z][A-Za-z0-9_]* -- type parameter $a1 $X
SCOPE ::= @[A-Za-z][A-Za-z0-9_]* -- block identifier @B1 @x
VAR ::= [a-z][A-Za-z0-9_]* -- variable identifier x f pt
TYPE ::= [A-Z][A-Za-z0-9_]* -- type identifier False Int Event
NAT ::= _[A-Za-z0-9_]* | _{...} | _(...) -- native identifier _errno _{(1+2)*x} _(char*)
TIMER ::= { [0-9]+ [`ms´|`s´|`min´|`h´] } -- timer identifier 1s 1h10min 20ms