Program | Comments | Declarations | Statements | Expressions | Conditions | Function Calls | Literals | Cvalues | Naming Conventions | Shadowing | Built-In Functions | Release 2 Built-Ins | Variadic Functions
A program is a set of declarations followed by a compound statement. Here is the minimal T3X program:
A comment is started with an exclamation point (!) and extends up to the end of the current line. Example:
DO END ! Do nothing
CONST name = cvalue, ... ;
Assign names to constant values.
CONST false = 0, true = %1;
VAR name, ... ;
VAR name[cvalue], ... ;
VAR name::cvalue, ... ;
Define variables, vectors, and byte vectors, respectively. Different definitions may be mixed. Vector elements start at an index of 0.
VAR stack[STACK_LEN], ptr;
STRUCT name = name_1, ..., name_N;
CONST name_1 = 0, ..., name_N = N-1, name = N;
Used to impose structure on vectors and byte vectors.
STRUCT POINT = PX, PY, PCOLOR; VAR p[POINT];
DECL name(cvalue), ... ;
Declare functions whose definitions follow later, where the cvalue is the number of arguments. Used to implement mutual recursion.
DECL odd(1); even(x) RETURN x=0-> 1: odd(x-1); odd(x) RETURN x=1-> 1: even(x-1);
name(name_1, ...) statement
Define function name with arguments name_1, ... and a
statement as its body. The number of arguments must match
DECL of the same function.
The arguments of a function are only visible within the (statement) of the function.
hello(s, x) DO VAR i; FOR (i=0, x) DO writes(s); writes("\n"); END END
Writes() writes a string.)
name := expression;
Assign the value of an expression to a variable.
DO VAR x; x := 123; END
name[value]... := value;
name::value := value;
Assign the value of an expression to an element of a vector or a byte vector. Multiple subscripts may be applied to to a vector:
vec[i][j]... := i*j;
vec[i][j] denotes the j'th element of the i'th
Note that the
:: operator is right-associative,
v::(x::i). This is particularly important when mixing
vec[i]::j[k] := 0;
would assign 0 to the
j[k]'th element of
(This makes sense, because
vec[i]::j would not deliver a valid
Call the function with the given name, passing the values of the expressions to the function. An empty set of parentheses is used to pass zero arguments. The result of the function is discarded.
For further details see the description of function calls in the expression section.
IF (condition) statement_1
IE (condition) statement_1 ELSE statement_2
Both of these statements run statement_1, if the given condition is true.
IE/ELSE runs statement_2, if the
conditions is false. In this case,
IF just passes control
to the subsequent statement.
IE (0) IF (1) RETURN 1; ELSE RETURN 2;
The example always returns 2, because only an
statement can have an
ELSE branch. There is no
"dangling else" problem.
WHILE (condition) statement
Repeat the statement while the condition is true. When the condition is not true initially, never run the statement.
! Count from 1 to 10 DO VAR i; i := 0; WHILE (i < 10) i := i+1; END
FOR (name=expression_1, expression_2, cvalue) statement
FOR (name=expression_1, expression_2) statement
Assign the value of expression_1 to name, then compare
name to expression_2. If cvalue is not negative, repeat
the statement while
name < expression_2. Otherwise repeat
the statement while
name > expression_2. After running the
statement, add cvalue to name. Formally:
name := expression_1; WHILE ( cvalue > 0 /\ name < expression \/ cvalue < 0 /\ name > expression ) DO statement; name := name + cvalue; END
When the cvalue is omitted, it defaults to 1.
DO VAR i; FOR (i=1, 11); ! count from 1 to 10 FOR (i=10, 0, %1); ! count from 10 to 1 END
Leave the innermost
passing control to the first statement following the loop.
DO VAR i; ! Count from 1 to 50 FOR (i=1, 100) IF (i=50) LEAVE; END
Re-enter the innermost
WHILE loops are re-entered at the point where the condition
is tested, and
FOR loops are re-entered at the point where
the counter is incremented.
DO VAR i; ! This program never prints X FOR (i=1, 10) DO LOOP; T.WRITE(1, "X", 1); END END
Return a value from a function. For further details see the description of function calls in the expression section.
inc(x) RETURN x+1;
Halt program and return the given exit code to the operating system.
DO statement ... END
DO declaration ... statement ... END
Compound statement of the form
used to place multiple statements in a context where only a single statement
is expected, like selection, loop, and function bodies.
A compound statement may declare its own local variables,
constant, and structures (using
STRUCT). A local variable of a compound statement is
created and allocated at the beginning of the statement is ceases to
exist at the end of the statement.
Note that the form
DO declaration ... END
also exists, but is essentially an empty statement.
DO var i, x; ! Compute 10 factorial x := 1; for (i=1, 10) x := x*i; END
These are both empty statements or null statements. They do not do anything when run and may be used as placeholders where a statement would be expected. They are also used to show that nothing is to be done in a specific situation, like in
IE (x = 0) ; ELSE IE (x < 0) statement; ELSE statement;
FOR (i=0, 100000) DO END ! waste some time
An expression is a variable or a literal or a function call or a set of operators applied to one of these. There are unary, binary, and ternary operators.
-a ! negate a b*c ! product of b and c x->y:z ! if x then y else z
In the following, the symbols X, Y, and Z denote variables or literals.
These operators exist (P denotes precedence, A associativity):
||9||L||the Y'th element of the vector X|
||9||R||the Y'th byte of the byte vector X|
||8||-||the negative value of X|
||8||-||the bitwise inverse of X|
||8||-||logical NOT of X|
||8||-||the address of X|
||7||L||the product of X and Y|
||7||L||the integer quotient of X and Y|
||7||L||the division remainder of X and Y|
||6||L||the sum of X and Y|
||6||L||the difference between X and Y|
||5||L||the bitwise AND of X and Y|
||5||L||the bitwise OR of X and Y|
||5||L||the bitwise XOR of X and Y|
||5||L||X shifted to the left by Y bits|
||5||L||X shifted to the right by Y bits|
||4||L||%1, if X is less than Y, else 0|
||4||L||%1, if X is less than Y, else 0|
||4||L||%1, if X is less/equal Y, else 0|
||4||L||%1, if X is greater/equal Y, else 0|
||3||L||%1, if X equals Y, else 0|
||3||L||%1, if X does not equal Y, else 0|
||2||L||if X then Y else 0 (short-circuit AND)|
||1||L||if X then X else Y (short-circuit OR)|
||0||-||if X then Y else Z|
Higher precedence means that an operator binds stronger, e.g.
-X::Y actually means
Left-associativity (L) means that
x+y+z = (x+y)+z and
right-associativity (R) means that
x::y::z = x::(y::z).
A condition is an expression appearing in a condition context,
like the condition of an
or the first operand of the
In an expression context, the value 0 is considered to be "false", and any other value is considered to be true.
X=X ! true 1=2 ! false "x" ! true 5>7 ! false
The canonical truth value, as returned by
When a function call appears in an expression, the result of
the function, as returned by
RETURN is used as an operand.
A function call is performed as follows:
Each actual argument in the call
is passed to the function and bound to the corresponding formal
argument ("argument") of the receiving function. The function
then runs its statement, which may produce a value via
RETURN statement exists in the statement, 0 is
Function arguments evaluate from the left to the right, so in
A is guaranteed to evaluate before B and C and B is guaranteed to evaluate before C.
pow(x, y) DO VAR a; a := 1; WHILE (y) DO a := a*x; y := y-1; END RETURN a; END DO VAR x; x := pow(2,10); END
An integer is a number representing its own value. Note that
negative numbers have a leading '
%' sign rather than a
-' sign. While the latter also works, it is, strictly
speaking, the application of the '
-' operator to a
positive number, so it may not appear in cvalue contexts.
0 12345 %1
Characters are integers internally. They are represented by single characters enclosed in single quotes. In addition, the same escape sequences as in strings may be used.
'x' '\\' ''' '\e'
A string is a byte vector filled with characters. Strings are
delimited by '
"' characters and NUL-terminated internally.
All characters between the delimiting double quotes represent
themselves. In addition, the following escape sequences may be
used to include some special characters:
|LF||Line Feed (newline)|
"" "hello, world!\n" "\qhi!\q, she said"
A table is a vector literal, i.e. a sequence of values. It is delimited by square brackets and elements are separated by commas. Table elements can be cvalues, strings, and tables.
[1, 2, 3] ["5 times -7", %35] [[1,0,0],[0,1,0],[0,0,1]]
The dynamic table is a special case of the table in which one or multiple elements are computed at program run time. Dynamic table elements are enclosed in parentheses. E.g. in the table
["x times 7", (x*7)]
the value of the second element would be computed and filled in when the table is being evaluated. Note that dynamic table elements are being replaced in situ, and remain the same only until they are replaced again.
Multiple dynamic elements may be enclosed by a single pair of parentheses. For instance, the following tables are the same:
[(x), (y), (z)] [(x, y, z)]
A cvalue (constant value) is an expression whose value is known at compile time. In full T3X, this is a large subset of full expressions, but in T3X9, it it limited to the following:
as well as (given that X and Y are one of the above):
Symbolic names for variables, constants, structures, and functions are constructed from the following alphabet:
_' and '
The first character of a name must be non-numeric, the remaining characters may be any of the above.
Upper and lower case is not distinguished, the symbolic names
FOO Foo foo
are all considered to be equal.
CONSTnames are all upper-case
STRUCTnames are all upper-case
VARnames are capitalized
VARnames are all lower-case
etc, are sometimes printed in upper case in documentation, but are
usually in lower case in actual programs.
There is a single name space without any shadowing in T3X:
The latter means that local names may be re-used in subsequent scopes, e.g.:
f(x) RETURN x; g(x) RETURN x;
would be a valid program. However,
f(x) DO VAR x; END !!! WRONG !!!
would not be a valid program, because
VAR x; redefines the
argument of F.
The following library functions exist in T3X9. They resemble the functions of the T3X core module of the full language, i.e. a T3X9 program can be compiled by a T3X compiler by adding the following code to the top of the program:
MODULE name(t3x); OBJECT t[t3x].
These functions are built into the T3X9 compiler, though, and
do not have to be declared in any way. The '
.' in the function
names resembles the message operator of the full language.
T.MEMCOMP(b1, b2, len)
Compare the first LEN bytes of the byte vectors B1 and B2. Return the difference of the first pair of mismatching bytes. A return code of 0 means that the compared regions are equal.
t.memcomp("aaa", "aba", 3) ! gives 'b'-'a' = %1
T.MEMCOPY(bs, bd, len)
Copy LEN bytes from the byte vector BS (source) to the byte vector BD (destination). Return 0.
DO VAR b:100; t.memcopy("hello", b, 5); END
T.MEMFILL(bv, b, len)
Fill the first LEN bytes of the byte vector BV with the byte value B. Return 0.
DO VAR b:100; t.memfill(b, 0, 100); END
T.MEMSCAN(bv, b, len)
Locate the first occurrence of the byte value B in the first LEN bytes of the byte vector BV and return its offset in the vector. When B does not exist in the given region, return -1.
t.memscan("aaab", 'b', 4) ! returns 3
T.READ(fd, buf, len)
Read up to LEN characters from the file descriptor FD into the buffer BUF. Return the number of characters actually read. Return -1 in case of an error.
DO b::100; t.read(0, b, 99); END
T.WRITE(fd, buf, len)
Write LEN characters from the buffer BUF to the file descriptor FD. Return the number of characters actually written. Return -1 in case of an error.
t.write(1, "hello, world!\n", 14);
The following functions are only available in T3X9 Release 2, but not in the compiler described in the book.
Create a file with the given PATH, open it, and return its file descriptor. In case of an error, return -1.
Open file PATH in the given MODE, where 0=read-only, 1=write-only, and 2=read/write. Return -1 in case of an error.
Close the file descriptor FD. Return 0 for success and -1 in case of an error.
DO var fd; fd := t.create("file"); if (fd >= 0) t.close(); END
Rename the file given in PATH to NEW. Return 0 for success and -1 in case of an error.
Remove the file given in PATH. Return 0 for success and -1 in case of an error.
T3X implements variadic functions (i.e. functions of a variable number of arguments) using dynamic tables. For instance, the following function returns the sum of a vector of arguments:
sum(k, v) DO var i, n; n := 0; FOR (i=0, k) n := n+v[i]; RETURN n; END
Its is an ordinary function returning the sum of a vector. It can be considered to be a variadic function, because a dynamic table can be passed to it in the V argument: