'boot' was the forerunner to SPAD and in FriCAS it is still the language that the interpreter is written in.
- It is written on top of Lisp (as macros) and its type system is the same as Lisp (essentially type-less).
- It has various higher level structures built on top of this.
In other words it has the syntax of SPAD and the semantics of Lisp (it takes the worst aspects of both?).
Since boot code has many problems I am making an attempt to convert boot code to SPAD code described on this page.
Functions
Function Calls
The syntax for the application of a function to its argument is like SPAD rather than Lisp.
| Lisp format | Boot format |
|---|---|
| (F X Y Z) | F(X,Y,Z) |
When F is a special Lisp word it will be written in Boot by using some other syntactic construction.
Function Definitions
The syntax of function definitions is similar to SPAD like this:
palindrome x ==
null x or x is [y] => true
x is [a, :y,=a] => palindrome y
false
note:
- == is used to define functions
- ==> is used to define macros
Boot Variables
As with Lisp there is only one variable type, like SExpression in SPAD, which can be either:
- String
- Symbol
- Integer
- Floating Point
or a recursively defined structure containing lists of these things.
Boolean in lisp: something is true if it is not NIL
In Lisp variable declaration may be performed in many ways, for instance:
- Declaring global (special) variables using defparameter and defvar
- declaring local variables with let, let*, multiple-value-bind, destructuring-bind, and other binding forms
- as function arguments.
Free variables are variables that have not been declared.
Boot has both lexical and dynamic variables.
Dynamic (AKA Special) variables are defined at the top level (outside function definitions) like this:
DEFPARAMETER ($dynParam , 1 ) DEFCONSTANT ( $dynConstant, 2 ) DEFCONST ( $dynConst, 3 ) DEFVAR' ( $dynVar )
Variables are dynamic if:
- They have a name starting with '$' (dollar).
- They are declared 'local' like this:
fluidVariable : local := 3
The effect of dynamic vs. lexical variable on its scope is illustrated in the diagrams below:
Lexical Variables
Scope is defined by block structure. |
Dynamic Variables
Scope is defined by execution path. |
Identifiers
The standard identifiers start with a letter (a-z or A-Z) dollar sign ($),question mark (?) , or the percent sign (%), and are followed by any number of letters, digits, single quotes('), question marks,or percent signs. It is possible however, by using the escape character (_), to construct identifiers that contain any characters except the blank or newline character. The rules in this case are that an escape character followed by any non-blank character will start an identifier with that character. Once an identifier has been started either in this way or by a letter, $, or %, then it may be continued either with a letter, digit ,',? or %, or with an escape character followed by any non-blank character.
For the syntax that I used to parse boot files see this page.
Numbers
Integers start with a digit (0-9) and are followed by any number of digits. The syntax for floating point numbers is <.I | I. | I.I> <<+ | - | empty> I where I is an integer.
Strings
Strings of characters are enclosed by double quote signs. They cannot span 2 or more lines and an escape character within a string will include the next character regardless of its nature. The meaning of a string depends somewhat on the context in which it is found, but in general a bare string denotes the interned atom making up its body whereas when it is preceded by a single quote (') it denotes the string of characters enclosed.
S-Expressions
An s-expression is preceded by a single quote and is followed by a Lisp s-expression.
sexpression ::=identifier | integer | MINUS integer | float | string
| QUOTE sexpression | parenthesized sexpression1
sexpression1 ::=sexpression (DOT sexpression | sexpression1)| empty
There are two ways to quote a name either 'name or "name", which both give rise to (QUOTE name). However a string that is a component of an sexpression will denote the string unless it is the sole component of the s-expression in which case it denotes a string i.e. '"name" gives rise to "name" in Lisp rather than (QUOTE "name").
Bindings
Normal Identifiers
Start with $
Global or dynamic variables.
Binding Rules
| Lexical | Free (global?) |
|---|---|
| function argument parameters | |
| variables assigned values | |
| other variables |
$ identifiers
| Dynamic | Free (global?) |
|---|---|
| function $ argument parameters | |
| $ variables declared local | |
| other $ variables |
Decomposition
Variables can be assigned inside lists by pattern matching.
So a single list is passed to this function and this is used to assign the variables a and b:
bizarreFunction([a,:b]) ==
[u for ( [c, :d] ) in b | u := f(a,c,d)]
When you want a value to have both a name and be decomposed use an assignment:
bizarreFunction(x := [a,:b]) ==
[u for (y := [c, :d] ) in b | u := f(a,c,d) or g(a,y)] or x
List Matching and Constructing Lists
In list matching:
| [a] | In this case variable 'a' on its own matches a single element of the list. | |
| [a,:b] | In this case variable 'b' matches multiple elements of the list. | |
| [a, . ] | dot is 'dont care' so this only matches to a 2 element list. | |
| [a, :. ] | :. is 'dont care' for any number of elements. | |
| [a, =a ] | '=' allows us to specify that the second element is the same as the first. |
':' colons can be used anywhere for constructing lists
| [a,:b] | CONS(a,b) |
| [:a,:b] | APPEND(a,b) |
In patterns colons can only be used once in a list.
'.' period = dont care.
| [:.,a] := u | sets a to last element of u |
For a discussion about how to covert lists in boot to SPAD see page here.
Calling lisp functions
(more information about lisp in Axiom/FriCAS on page here)
Several lisp values have lower case designations:
|
|
Keywords
The table of key words follows, each is given an upper case
name for use in the description of the syntax.
as written name
and AND
by BY
cross CROSS
else ELSE
for FOR
if IF
in IN
is IS
isnt ISNT
or OR
repeat REPEAT
return RETURN
then THEN
until UNTIL
where WHERE
while WHILE
. DOT
: COLON
, COMMA
; SEMICOLON
* TIMES
** POWER
/ SLASH
+ PLUS
- MINUS
< LT
> GT
<= LE
>= GE
= EQ
^ NOT
^= NE
.. SEG
# SIZE
=> EXIT
:= BECOMES
== DEF
==> MDEF
( OPAREN
) CPAREN
[ OBRACK
(| OBRACK
] CBRACK
|) CBRACK
| BAR
suchthat BAR
Is and Isnt
'is' returns true if it can pattern match a list: palindrome x ==
null x or x is [y] => true
x is [a, :y,=a] => palindrome y
false
where x is [y] is true if x is a single element list. x is [a, :y,=a] is true if the first and last elements are the same. |
Example (from here): |
isRecord type == type is ['Record,:.] |
For a discussion about how to covert 'is' in boot to SPAD see page here.
In
The iteration x in tails x causes x to take on the values u, CDR u, CDR CDR u ... until a null tail is reached. beforeAfter(x,u) == [[y for [y,:r] in tails u while x ¬= y],r] splits list 'u' into parts before and after the marker: (beforeAfter 'x '(a b c x d e)) -> ((a b c) (d e)) |
Example (from here): |
dom.5 := [rest a for a in args] |
For a discussion about how to covert 'in' in boot to SPAD see page here.
Return
| The prefix operator 'return' is used to exit from a binding contour. Thus, a return inside the body of a loop will exit from the loop not the function. | Example (from here): |
itl:= [([.,$e]:= compIterator(x,$e) or return "failed").(0) for x in itl] itl="failed" => return nil |
For a discussion about how to covert 'return' in boot to SPAD see page here.
Where Clause
The argument to a 'where' clause can be a pile of definitions of functions and macros. So a 'where' clause allows us to create local functions. |
Example (from here): |
T:=
[x',m',e'] where
m':= SUBLIS(sl,map.(1))
x':=
form':= [f,:[t.expr for t in Tl]]
(m'=$Category or isCategoryForm(m',e)) and ATOM(f) => form'
-- try to deal with new-style Unions where we know the conditions
op = "elt" and f is ['XLAM,:.] and IDENTP(z := first argl) and
(c:=get(z,'condition,e)) and
c is [["case", =z, c1]] and
(c1 is ['_:,=(CADR argl),=m] or EQ(c1,CADR argl) ) =>
|
For a discussion about how to covert 'where' in boot to SPAD see page here.
Tracing boot code
| )t f1 | trace function f1 |
| )t | what is traced |
| )t )off | untrace all functions |
| )t f1 )off | untrace f1 |
| )t )debth n | trace to limited number of recursions |
| )t f1 )vars v1 | trace assignments to v1 in f1 |
Boot Syntax
I have put some code for parsing boot code here.
Documentation
http://daly.axiom-developer.org/boot.tgz
From Doc
The following is from the documentation.
BOOT TO COMMON LISP TRANSLATER
INTRODUCTION
The Scratchpad language is implemented by using a mixture of Lisp and
a more convenient language for writing Lisp called "Boot".
This document contains a description of the Boot language, and some
details of the resulting Lisp programs.
The description of the translation
functions available are at the end of this file.
Boot contains an easy method of writing expressions that denote lists,
and provides an analogous method of writing patterns containing variables
and constants which denote a particular class of lists. The pattern
is matched against a particular list at run time,
and if the list belongs to the class then its variables will
take on the values of components of the list.
A second convenient feature provided by Boot is a method of
writing programs that iterate over the elements of one or more lists
and which either transform the state of the machine, or
produce some object from the list or lists.
LINES AND COMMANDS
If the first character of a line is a closing parenthesis the line
is treated as a command which controls the lines that will be
passed to the translater rather than being passed itself.
The command )include filename filemodifier will for example
be replaced by the lines in the file filename filemodifier.
If a line starts with a closing parenthesis it will be called a command
line, otherwise it will be called a plain line.
The command lines are
name as written
Include )include filename filemodifier
IncludeLisp )includelisp filename filemodifier
If )if bootexpression
Else )else
ElseIf )elseif bootexpression
EndIf )endif
Fin )fin
Say )say string
Eval )eval bootexpression
EvalStrings )evalstrings bootexpression
Package )package packagename
SimpleLine::= PlainLine | Include | IncludeLisp |Say | Eval | EvalStrings
| Package
A PlainLine is delivered to the translater as is.
An Include delivers the lines in the file filename.filemodifier,
treated as boot lines.
An IncludeLisp delivers the lines in the specified file, treated as lisp
lines. The only comments allowed in lisp files that are included in
this way require that the semicolon is at the beginning of the line.
A Say outputs the remainder of the line to the console,
delivering nothing to the translater.
An Eval translates the reminder of the line, assumed to be
written in Boot, to Lisp, and evaluates it, delivering nothing to
the translater.
An EvalStrings also translates and evaluates the rest of the line
but this time assumes that the Boot expression denotes a list
of strings which are then delivered to the translater
instead of the EvalString line. The strings are treated as Boot lines.
It is also possible to include or exclude lines based upon some
condition which is the result of translating and evaluating
the boot expression that follows an )if or )elseif command.
This construction will be called a Conditional. A file will be
composed from SimpleLines and Conditionals. A file is either
terminated by the end of file or by a Fin line.
Components ::=(SimpleLine | Conditional)*
File ::= Components ( Fin | empty)
A conditional is bracketed by an If and an EndIf.
Conditional ::= If Components Elselines EndIf
If the boot expression following the )if has value true then the
Components are delivered but not the ElseLines,
otherwise the Components are ignored ,and the ElseLines
are delivered to the translater. In any case the lines after
the EndIf are then processed.
ElseLines ::= Else Components | ElseIf Components ElseLines | empty
When the Elselines of a Conditional is being included then if an
"Else Components" phrase is encountered then the following
Components are included
otherwise if an "ElseIf Components ElseLines" phrase is encountered then
the boot expression following the )elseif is evaluated and
if true the following Components are included, if false the
following ElseLines is included.
BOOT SYNTAX
SYNTAX
PRIMARY
constant::= integer | string | float | sexpression
The value of a constant does not depend on the context in which it
is found.
primary::= name | constant | construct | block | tuple | pile
The primaries are the simplest constituents of the language and
either denote some object or perform some transformation of the
machine state, or both.
The statements are the largest constituents and enclosing them
in parentheses converts them into a primary.
An alternative method of grouping uses indentation to indicate the
parenthetical structure.
A number of lines whose first non-space characters are in the same
column will be called a "pile". The translater first tokenizes the
lines producing identifier, key word, integer, string or float tokens,
and then examines the pile structure of a Boot program
in order to add additional tokens called SETTAB,BACKTAB and BACKSET.
These tokens may be considered as commands for creating a pile.
The SETTAB starts a new line indented from the previous line and
pushes the resulting column number on to a stack of tab positions.
The BACKTAB will start a new line at the column position found
at the head of the stack and removes it from the stack.
The BACKSET has the same effect as a BACKTAB immediately followed
by a SETTAB.
The meaning of a sequence of tokens containing SETTAB
BACKTAB and BACKSET is the same the sequence in which each
SETTAB is replaced by OPAREN , each BACKTAB is replaced by
CPAREN , and each BACKSET is replaced by SEMICOLON. By
construction the BACKTABS and SETTABS are properly nested.
listof(p,s)== p | p s ... s p
parenthesized s ::= OPAREN s CPAREN
piled s ::= SETTAB s BACKTAB
blockof s ::= parenthesized (listof (s,SEMICOLON))
pileof s ::= piled (listof (s,BACKSET ))
A pileof s has the same meaning as a blockof s.
There is however a slight difference because piling is weaker than
separation by semicolons. In other words the pile items
may be listof(s,SEMICOLON).
In other words if statements::= listof(statement,SEMICOLON) then
we can have a pileof statements which has the same meaning as
the flattened sequence formed by replacing
all BACKSET's by SEMICOLON's.
A blockof statement is translated to a compound statement
e.g. in the absence of any exits,
(a;b;c;d) is translated to (PROGN a b c d).
APPLICATION
SELECTORS
selector::= leftassociative(primary, DOT)
A selector a.b denotes some component of a structure, and in
general is translated to (ELT a b). There are some special identifiers
that may be used in the b position to denote list components, of which
more later.
The DOT has a greater precedence than juxtaposition and is
left associative, For example
a.b.c is grouped as (a.b).c which is translated to
(ELT (ELT a b) c)
application ::= selector selector ... selector
Application of function to argument is denoted by juxtaposition.
A sequence of selectors is right associative and so
f g h x is grouped as f(g(h x)). The applications f x and f(x)
mean the application of f to x and get translated to
the Lisp (f x). The application of a function to the empty list
is written f(), meaning the Lisp (f). f(x,y,z) gets translated to
the Lisp (f x y z).
Common Lisp does not permit a variable to occur in operator position,
so that when f is a variable its application has to be
put in argument position of a FUNCALL or APPLY.
f(x,y,z) has to be replaced by FUNCALL(f,x,y) which gets translated to
the Lisp (FUNCALL f x y z).
In Common Lisp each symbol might refer
to two objects a function and a non-function. In order to resolve
this ambiguity when a function symbol appears in a context other
than operator position it has to be preceded by the symbol FUNCTION.
Also it is possible to produce the function type symbol from the
non-function symbol by applying SYMBOL-FUNCTION to it.
Certain reserved words called infixed operators namely
POWER, TIMES, SLASH, PLUS MINUS ,IS,
EQ , NE , GT , GE , LT , LE , IN , AND, OR,
indicate application by being placed between their 2 arguments.
Infixed application may be either right- or left-associative.
rightassociative(p,o)::= p o p o p o ... o p
== p o (p o (p o ... o p)))
leftassociative(p,o)::= p o p o p o ... o p
== (((p o p) o p) o ...) o p
exponent ::= rightassociative(application,POWER)
reduction ::= (infixedoperator |string | thetaname) SLASH application
In a reduction the application denotes a list of items and
operator SLASH application accumulates the list elements from the
left using the operator
e.g. +/[a,b,c] means (((0+a)+b)+c)
Only certain operators are provided with values when the list is empty
they are and, or +, *, max, min, append, union. However any
function can be used as an operator by enclosing it in double
quotes. In this case the reduction is not applicable to an
empty list.
multiplication ::= rightassociative(exponent,TIMES|SLASH) | reduction
minus ::= MINUS multiplication | multiplication
arith ::= leftasscociative(minus,PLUS | MINUS)
is ::= arith | arith (IS | ISNT) pattern
comparison ::= is (EQ | NE | GT | GE | LT | LE | IN) is | is
and ::= leftassociative (comparison,AND)
return ::= and | RETURN and
expression ::= leftassociative(return,OR)
The infixed operators denote application of the function to its
two arguments. To summarize,
the infixed operators are, in order of decreasing precedence
strengths.
.
juxtaposition
**
* /
+ -
is
= ^= > >= < <= in
and
or
CONDITIONALS
conditional ::= IF where THEN where |
IF where THEN where ELSE where
IF a THEN b is translated to (COND (a b)) and
IF a THEN b else c is translated to (COND (a b) (T c))
statement::= conditional | loop | expression
LOOPS
loop ::= crossproduct REPEAT statement | REPEAT statement
iterator ::= forin | suchthat | until | while
iterators ::= iterator iterator ... iterator
crossproduct ::=rightassociative(iterators,CROSS)
suchthat ::= BAR where
while ::= WHILE expression
until ::= UNTIL expression
forin ::= for variable IN segment |
for variable IN segment BY arith
segment::= arith | arith SEG arith | arith SEG
A loop performs an iterated transformation of the state which is
specified by its statement component and its iterators.
The forin construction introduces a new variable which is assigned
the elements of the list which is the value of the segment in the order
in which they appear in the list .
A segment of the form arith denotes a list,
and segments of the form "arith SEG arith" and
"arith SEG" denote terminating and non-terminating
arithmetic progressions.
The "BY arith" option is the step size, if omitted the step is 1.
Two or more forin's may control a loop.
The associated lists are scanned in parallel and
a variable of one forin may not appear in the segment expression that
denotes the list in a second forin.
Such a variable may however occur in the conditions for filtering or
introduced by a suchthat, or for termination introduced by a
while iterator, and in the statement of the loop.
The forin variables are local to the statement, the conditions
that follow a while or suchthat in the same list of iterators and
have no meaning outside them.
The loop will be terminated when one of its forin lists is null, or
if the condition in a while is not satisfied. The list
elements are filtered by all the suchthat conditions.
The ordering of the iterators is irrelevant to the meaning, so it is
best to avoid side effects within the conditions for filtering and
termination.
It is possible to control a loop by using a cross-product of iterators.
The iteration in the case iterators1 CROSS iterators2 is over
all pairs of list items one from the list denoted by
iterators1 and the other from the list denoted by iterators2.
In this case the variables introduced forin statements in iterators1
may be used in iterators2.
LISTS
Boot contains a simple way of specifying lists that are constructed
by CONS and APPEND, or by transforming one list to another in a
systematic manner.
construct ::= OBRACK construction CBRACK
construction ::= comma | comma iteratortail
iteratortail ::= REPEAT iterators | iterators
A construct expression denotes a list and may also have a list
of controlling iterators having the same syntax as a loop. In this
case the expression is enclosed in brackets and the iterators follow
the expression they qualify, rather than preceding it.
In the case that there are no iterators the construct expression
denotes a list by listing its components separated by commas, or by
a comma followed by a colon. In the simple case in which there are no
colons the Boot expression [a,b,c,d] translates to the Lisp
(LIST a b c d) or (CONS a (CONS b (CONS c (CONS d NIL)))).
When elements are separated by comma colon, however, the expression
that follows will be assumed to denote a list which will be appended
to the following list, rather than consed. An exception to this rule
is that a colon preceding the last expression is translated to
the expression itself. If it immediately preceded by a CONS
then it need not denote a list.
For example:
[] is translated to the empty list NIL
[a] is translated to the 1-list (LIST a) or (CONS a NIL)
[:a] is translated to a
[a,b] is translated to the 2-list (LIST a b) or (CONS a (CONS b NIL))
[:a,b] is translated to (APPEND a (CONS b NIL))
[a,:b] is translated to (CONS a b)
[:a,:b] is translated to (APPEND a b)
[:a,b,c] is translated to (APPEND a (CONS b (CONS c NIL)))
[a,:b,c] is translated to (CONS a (APPEND b (CONS c NIL)))
[a,b,:c] is translated to (CONS a (CONS b c))
If the construct expression has iterators that control the production
of the list the resulting list depends on the form of the comma
expression.
i.e.
construction ::= comma iteratortail
If the comma expression is recognised as denoting a list
by either preceding it by a colon, or having commas at top level
as above, then the successive values are appended. If not then
the successive values are consed.
e.g.
[f i for i in x] denotes the list formed by applying f to each
member of the list x.
[:f i for i in 0..n] denotes the list formed by appending the
lists f i for each i in 0..n.
PATTERNS
is ::= arith | arith IS pattern
The pattern in the proposition "arith IS pattern" has the same form
as the construct phrase without iterators. In this case, however it
denotes a class of lists rather than a list, and is composed
from identifiers rather than expressions. The proposition
is translated into a program that tests whether the arith expression
denotes a list that belongs to the class. If it does then the value
of the is expression is true and the identifiers in
the pattern are assigned the values of the corresponding
components of the list. If the list does not match the pattern
the value of the is expression is false and the values of the
identifier might be changed in some unknown way that reflects the
partial success of the matching.
Because of this uncertainty,
it is advisable to use the variables in a pattern
as new definitions rather than assigning to variables that are
defined elsewhere.
pattern::= identifier | constant | [ patternlist ]
The value of arith IS identifier is true and the value of arith
is assigned to the identifier.
(PROGN (SETQ identifier arith) T)
The expression arith IS constant is translated to (EQUAL constant arith).
The expression arith IS [ pattenlist ]
produces a program which tests whether arith denotes a list
of the right length and that each patternitem matches the corresponding
list component.
patternitem ::= EQ application | DOT | pattern | name := pattern
If the patternitem is EQ application then the value is true if
the component is EQUAL to the value of the application expression.
If the patternitem is DOT then the value is true regardless of the
nature of the component. It is used as a place-holder to test
whether the component exists.
If the patternitem is pattern then the component is matched against
the pattern as above.
If the patternitem is name:=pattern then the component is matched against
the pattern as above, and if the value is true the component is assigned
to the name. This last provision enables both a component and
its components to be given names.
patternlist ::= listof(patternitem,COMMA)|
listof(patternitem,COMMA) COMMA patterntail
patterntail
patterncolon ::= COLON patternitem
patterntail ::= patterncolon |
patterncolon COMMA listof(patternitem,COMMA)
The patternlist may contain one colon to indicate that the following
patternitem can match a list of any length. In this case
the matching rule is to construct the expression
with CONS and APPEND from the pattern as shown above and then test
whether the list can be constructed in this way, and if so
deduce the components and assign them to identifiers.
The effect of a pattern that occurs as a variable in a for iterator
is to filter the list by the pattern.
forin ::= for pattern IN segment
is translated to two iterators
for g IN segment | g IS pattern
where g is an invented identifier.
forin ::= for (name:=pattern) IN segment
is translated to two iterators
for name IN segment BAR name IS pattern
in order to both filter the list elements, and name both elements and
their components.
ASSIGNMENTS
A pattern may also occur on the left hand side of an assignment
statement, and has a slightly different meaning.
The purpose in this case is to give names to the components
of the list which is the value of the right hand side.
In this case no checking
is done that the list matches the pattern precisely and the only
effect is to construct the selectors that correspond to
the identifiers in the pattern, apply them to the value of the
right hand side and assign the selected components
to the corresponding identifiers.
The effect of applying CAR or CDR to arguments to which they are not
applicable will depend on the underlying Lisp system.
assignment::= assignvariable BECOMES assignment| statement
assignvariable := OBRACK patternlist CBRACK | assignlhs
The assignment having a pattern as its left hand side is reduced
as explained above to one or more assignments having an identifier
on the left hand side.
The meaning of the assignment depends on whether the identifier
starts with a dollar sign or not, if it is and whether it is followed by
:local or :fluid.
If the identifier does not start with a dollar sign it
is treated as local to the body of the function in which it
occurs, and
if it is not already an argument of the function,
a declaration to that effect is added to the Lisp code
by adding a PROG construction at top level within the body of the
function definition.
If such an identifier assignment does not occur in the body
of a function but in a top level expression then
it is also treated as a local. The sole exception to this rule
is when the top level expression is an assignment to an identifier
in which case it is treated as global.
If the left hand side of an assignment is an identifier that starts with
a dollar sign it will not be classified as a local but will
be treated as non-local. If it is also followed by :local then it
will be treated as a declaration of a FLUID (VMLisp) or SPECIAL
variable (Common Lisp) which will be given an initial value which is the
value of the right hand side of the assignment statement.
The FLUID or SPECIAL variables may be referred to or assigned to
by functions that are applied in the body of the declaration.
If the left hand side of an assignment statement is
an identifier that does not start with a dollar sign followed
by :local then it will also be treated as a FLUID or SPECIAL
declaration, however it may only be assigned to in the body
of the function in which the assignment it occurs.
assignment::= assignvariable BECOMES assignment | statement
assignvariable := OBRACK patternlist CBRACK | assignlhs
assignlhs::= name | name COLON local |
name DOT primary DOT ... DOT primary
If the left hand side of an assignment has the form
name DOT primary DOT ... DOT primary
the assignment statement will denote an updating of some component
of the value of name. In general name DOT primary := statement
will get translated to (SETELT name primary statement) or
(SETF (ELT name primary) statement)
There are however certain identifiers that denote components of
a list which will get translated to statements that update that
component (see appendix) e.g. a.car:=b is translated to
(SETF (CAR a) b) in Common Lisp.
The iterated DOT is used to update components of components
and e.g a.b.c:=d is translated to (SETF (ELT (ELT a b)c) d)
exit::= assignment | assignment EXIT where
The exit format "assignment EXIT where" is used to give a value to
a blockof or pileof statements in which it occurs at top level.
The expression
(a =>b;c) will be translated to if a then b else c or
(COND (a b) (T c))
If the exit is not a component of a blockof or pileof statements
then a=>b will be translated to (COND (a b))
DEFINITIONS
Functions may be defined using the syntax
functiondefinition::= name DEF where | name variable DEF where
variable ::= parenthesized variablelist | pattern
variableitem ::=
name| pattern | name BECOMES pattern | name IS pattern
variablelist ::= variableitem | COLON name |
variableitem COMMA variablelist
Function definitions may only occur at to level or after a where.
The name is the name of the function being defined, and the
most frequently used form of the variable is either a single name
or a parenthesized list of names separated by commas.
In this case the translation to Lisp is straightforward, for example:
f x == E or f(x)==E is translated to (DEFUN f (x) TE)
f (x,y,z)==E is translated to (DEFUN f (x y z) TE)
f ()==E is translated to (DEFUN f () TE)
where TE is the translation of E.
At top level f==E is translated to (DEFUN f () TE)
The function being defined is that which when applied to its arguments
produces the value of the body as result where the variables
in the body take on the values of its arguments.
A pattern may also occur in the variable of a definition of a function
and serves the purpose, similar to the left hand side of assignments,
of naming the list components.
The phrase
name pattern DEF where
is translated to
name g DEF (pattern:=g;where)
similarly
name1 name2 := pattern DEF where or name1 name2 is pattern DEF where
are both translated to
name1 name2 DEF (pattern:=name2;where)
similarly for patterns that occur as components of a list of
variables. order
variablelist ::=
variableitem | COLON name | variableitem COMMA variablelist
The parenthesized variablelist that occurs as a variable of a function
definition can contain variables separated by commas but can also
have a comma colon as its last separator.
This means that the function is applicable to lists of different
sizes and that only the first few elements corresponding to the
variables separated by commas are named, and
the last name after the colon denotes the rest of the list.
Macros may be defined only at top level, and must always have a variable
macrodefinition::= name variable MDEF where
The effect of a macrodefinition is to produce a Lisp macro
which is applied to arguments that are treated as expressions, rather
than their values, and whose result if formed by first substituting
the expressions for occurrences of the variables within the body
and then evaluating the resulting expression.
WHERE CLAUSES
Expressions may be qualified by one or more function definitions
using the syntax
where ::= exit | exit WHERE qualifier
qualifier ::= functiondefinition |
pileof (functiondefinition) | blockof functiondefinition
The functions may only be used within the expression that is qualified.
This feature has to be used with some care, however, because
a where clause may only occur within a function body, and
the component functions are extruded, so to speak, from their contexts
renamed, and made into top level function definitions.
As a result the variables of the outer function cannot be referred to
within the inner function.
If a qualifying function has the format "name DEF where" then
the where phrase is substituted for all occurences of the name
within the expression qualified.
If an expression is qualified by a phrase that is not a
function definition then the result will be a compound statement
in which the qualifying phrase is followed by the qualified phrase.
TUPLES
Although a tuple may appear syntactically
in any position occupied by a primary
it will only be given meaning when it is the argument to a function.
To denote a list it has to be enclosed in brackets rather than
parentheses. A tuple at top level is treated as if its components
appeared at top level in the order of the list.
tuple::= parenthesized (listof (where,COMMA))
BLOCKS AND PILES
block::= parenthesized (listof (where,SEMICOLON))
pile::= piled (listof (listof(where,SEMICOLON),BACKSET))
A block or a pile get translated to a compound statement or PROGN
TOP LEVEL
toplevel ::= functiondefinition | macrodefinition | primary
TRANSLATION FUNCTIONS
(boottocl "filename")
translates the file "filename.boot" to the common lisp file
"filename.clisp"
(bootclam "filename")
translates the file "filename.boot" to the common lisp file
"filename.clisp" , producing, for each function a
hash table to store previously computed values indexed by argument
list. The function first looks in the hash table for the result
if there returns it, if not computes the result and stores it in the
table.
(boottoclc "filename")
translates the file "filename.boot" to
the common lisp file "filename.oclisp" with the original boot
code as comments
(boot "filename")
translates the file "filename.boot" to
the common lisp file "filename.clisp", compiles it to the file
"filename.bbin" and loads the bbin file.
(bo "filename")
translates the file "filename.boot"
and prints the result at the console
(stout "string")
translates the string "string" and prints the result at the console
(sttomc "string")
translates the string "string" to common lisp, and compiles the result.
(fc "functionname" "filename")
attempts to find the boot function
functionname in the file filename, if found it translates it to common
lisp, compiles and loads it.
BOOT_-COMPILE_-DEFINITION_-FROM_-FILE(fn,symbol)
is similar to fc, fn is the file name but symbol is the symbol
of the function name rather than the string.
(fn,symbol)
BOOT_-EVAL_-DEFINITION_-FROM_-FILE(fn,symbol)
attempts to find the definition of symbol in file fn, but this time
translation is followed by EVAL rather than COMPILE
(defuse "filename")
Translates the file filename, and writes a report of the
functions defined and not used, and used and not defined in the
file filename.defuse
(xref "filename")
Translates the file filename, and writes a report of the
names used, and where used to the file filename.xref |
