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= Expressions = Here is the grammar of expressions `E`. As is standard in ML-family languages and Haskell, juxtaposition is used to represent function application, with application associating to the left. || '''Syntax''' || '''Description''' || '''Typing''' || || `Int` || Integer constant || `G |- Int : int` || || `String` || String constant || `G |- String : string` || || `[E1, ..., EN]` || List || If `G |- Ei : T` for each `Ei`, then `G |- [E1, ..., EN] : [T]`. || || `Symbol` || Variable || `G1, Symbol : T, G2 |- Symbol : T`. || || `E1 E2` || Application || If `G |- E1 : T1 -> T2` and `G |- E2 : T1`, then `G |- E1 E2 : T2`. || || `\ Symbol -> E` || Abstraction (inferred domain type) || If `G, Symbol : T1 |- E : T2`, then `G |- \ Symbol -> E : T1 -> T2`. || || `\ Symbol : (T1) -> E` || Abstraction (explicit domain type) || If `G, Symbol : T1 |- E : T2`, then `G |- \ Symbol : (T1) -> E : T1 -> T2`. || || `CSymbol = E` || Environment variable set || See subsection on actions || || `Symbol <- CSymbol; E` || Environment variable get || See subsection on actions || || `E1; E2` || Sequencing || See subsection on actions || || `E1 where E2 end` || Local bindings || See subsection on actions || || `let E1 in E2 end` || Local bindings || See subsection on actions || || `E1 with E2 end` || Nested action || See subsection on actions || || `E1 with end` || Empty nested action || See subsection on actions || || `E1 where E2 with E3 end` || Nested action with local bindings || See subsection on actions || || `E1 where E2 with end` || Empty nested action with local bindings || See subsection on actions || || `\\ Symbol : P -> E` || Nested action abstraction || See subsection on actions || |
This page gives an in-depth specification of the DomTool language. Most members would probably prefer the more informal presentation in DomTool/UserGuide.
1. Source code
For a complete, precise, and accurate grammatical specification, see the lexer and parser specifications src/domtool.lex and src/domtool.grm in the DomTool source code. See src/tycheck.sml for the type-checker implementation. ["DomTool/Building"] has information on obtaining the source.
2. Token conventions
In the grammars that follow, we use these lexical token class names:
Name |
Description |
Int |
Integer constant |
String |
String constant (enclosed in double quotes) |
Symbol |
Identifier starting with a lowercase letter |
CSymbol |
Identifier starting with a capital letter |
3. Predicates
DomTool uses predicates to describe in what contexts an action may occur. For instance, web-related actions should only occur inside the scope of a virtual host directive. Predicates are built up following the grammar in the table below, using the letter P as the non-terminal for predicates.
Meanings are given as statements that must hold about the context where an action is found. The context is represented as a stack of context IDs which have been declared with context declarations.
Syntax |
Description |
Meaning |
Root |
Root |
The stack is empty. |
CSymbol |
Context ID |
CSymbol is on the top of the stack. |
^P |
Suffixes |
Some (not necessarily strict) suffix of the stack matches P. |
!P |
Not |
The stack doesn't match P. |
P1 & P2 |
And |
The stack matches both P1 and P2. |
(P) |
Grouping |
Identical to P |
4. Types
Types describe expressions. As is standard in statically-typed programming languages, they are used only for validation purposes and have no real effect on the "output" of a program. The following table gives the grammar of types T. The section on expressions will give the meanings of types in terms of which expressions have which types.
Syntax |
Description |
Symbol |
Extern type |
[T] |
List of Ts |
T1 -> T2 |
Function from T1 to T2 |
[P] |
Action allowed only when P is satisified; requires no environment variables on input and writes none of its own |
[P] {CSymbol1 : T1, ..., CSymbolN : TN} |
Action that requires environment variables CSymbol1, ..., CSymbolN to have the given types when run |
[P] {CSymbol1_1 : T1_1, ..., CSymbol1_N : T1_N} => {CSymbol2_1 : T2_1, ..., CSymbol2_M : T2_M} |
Like the last case, but the second set of typed environment variables describes what the action will write |
P => T |
A nested action that requires that its nested configuration satisfy P; T should be some action type |
(T) |
Grouping |
5. Expressions
Here is the grammar of expressions E. As is standard in ML-family languages and Haskell, juxtaposition is used to represent function application, with application associating to the left.
Syntax |
Description |
Typing |
Int |
Integer constant |
G |- Int : int |
String |
String constant |
G |- String : string |
[E1, ..., EN] |
List |
If G |- Ei : T for each Ei, then G |- [E1, ..., EN] : [T]. |
Symbol |
Variable |
G1, Symbol : T, G2 |- Symbol : T. |
E1 E2 |
Application |
If G |- E1 : T1 -> T2 and G |- E2 : T1, then G |- E1 E2 : T2. |
\ Symbol -> E |
Abstraction (inferred domain type) |
If G, Symbol : T1 |- E : T2, then G |- \ Symbol -> E : T1 -> T2. |
\ Symbol : (T1) -> E |
Abstraction (explicit domain type) |
If G, Symbol : T1 |- E : T2, then G |- \ Symbol : (T1) -> E : T1 -> T2. |
CSymbol = E |
Environment variable set |
See subsection on actions |
Symbol <- CSymbol; E |
Environment variable get |
See subsection on actions |
E1; E2 |
Sequencing |
See subsection on actions |
E1 where E2 end |
Local bindings |
See subsection on actions |
let E1 in E2 end |
Local bindings |
See subsection on actions |
E1 with E2 end |
Nested action |
See subsection on actions |
E1 with end |
Empty nested action |
See subsection on actions |
E1 where E2 with E3 end |
Nested action with local bindings |
See subsection on actions |
E1 where E2 with end |
Empty nested action with local bindings |
See subsection on actions |
\\ Symbol : P -> E |
Nested action abstraction |
See subsection on actions |