It is a simple programming language step-by-step implementation using DCG-parsing power. It also evaluates a code and optinally builds a parse tree. It is tested with gprolog (1.4.4) but it possibly can be used with other prolog translators. It can be used as an example of a simple DCG-parser development.
Step 1. It is a calculator for the real arithmetic. It works with any formula compliant with the next grammar in BNF:
Input → Expression | nothing Expression → Term Expression_rest Expression_rest → + Term Expression_rest | - Term Expression_rest | nothing Term → Factor Term_Rest Term_Rest → * Factor Term_Rest | / Factor Term_Rest | nothing Factor → Element ^ Factor | - Factor | + Factor | Element Element → ( Expression ) | number
Use `hoc1.pro' for this step. Use `hoc1x.pro' if you want to have a parse tree. The tree is printed in text linear form by default. If a graphic tree is required use the aim hoc1g to produce a file in dot-format.
Step 2. It is missed. It supposes an addition of a support for one letter named variables.
Step 3. It is a calculator for the real arithmetic with constants (pi, e, phi), built-in functions (sin, ln, sqrt, arctg, log2, fib), and variables. It works with any formula compliant with the next grammar in BNF:
Input → Assignment | Expression | nothing Assignment → identifier = Expression Expression → Term Expression_rest | Assignment Expression_rest → + Term Expression_rest | - Term Expression_rest | nothing Term → Factor Term_rest Term_rest → * Factor Term_rest | / Factor Term_rest | nothing Factor → Element ^ Factor | - Factor | + Factor | Element Element → ( Expression ) | built_in ( Expression ) | identifier | number
Use `hoc3.pro' for this step. Use `hoc3x.pro' if you want to have a parse tree. For a graphic tree use the aim hoc3g as usual. The file `hoc3.pl' is a wrapper to use it for swi-prolog – it gives the idea how to use such wrappers with other samples.
Step 4. It is for the same language but it generates a code and later executes it. It allows to add the support for the programming language statements later. This impementation contains an interpreter which executes the generated codes. The previous implementations just evaluate an inputted text immediately. Use `hoc4.pro' for this step.
Step 5. It adds C-like relational operators (<, >, ==, !==, <=, >=), C-like logical operators (||, &&, !), loop (while), conditional (if) and print statements. It also prints the stream of entered lexemes and the result of translation in RPN.
Input → Assignment | Formula | Statement | nothing Statement → while Condition Statement
| print Formula
| if Condition Statement else Statement
| if Condition Statement
| { Statement_list }
| Formula Statement_list → Statement Statement_list | nothing Formula → Relation Formula_rest | Assignment Formula_rest → && Relation Formula_rest | || Relation Formula_rest | nothing Relation → Expression == Expression | Expression != Expression | Expression <= Expression | Expression >= Expression | Expression > Expression | Expression < Expression | Expression Assignment → Lvalue = Formula Expression → Term Expression_rest Expression_rest → + Term Expression_rest | - Term Expression_rest | nothing Term → Factor Term_Rest Term_Rest → * Factor Term_Rest | / Factor Term_Rest | nothing Factor → Element ^ Factor | - Factor | + Factor | Element Element → Condition | ! Element | built_in ( Expression ) | identifier | number Condition → ( Formula ) Lvalue → identifier
Use `hoc5.pro' for this step. Use `hoc5x.pro' if you want to have a parse tree. For a graphic tree use the aim hoc5g.
Step 6. It adds support for string output and subroutines (procedures and functions).
Input → Assignment | Formula | Statement | Define_function | nothing
Define_function → func Lvalue () Statement | proc Lvalue () Statement
Statement → while Condition Statement
| print Print_list
| if Condition Statement else Statement
| if Condition Statement
| { Statement_list }
| Procedure_call ( Argument_list )
| return Formula
| return
| Formula
Argument_list → Formula , Argument_list | Formula | nothing
Statement_list → Statement Statement_list | nothing
Formula → Relation Formula_rest | Assignment
Formula_rest → && Relation Formula_rest | || Relation Formula_rest | nothing
Relation → Expression == Expression | Expression != Expression | Expression <= Expression
| Expression >= Expression | Expression > Expression | Expression < Expression | Expression
Assignment → Lvalue = Formula | Local_id = Formula
Expression → Term Expression_rest
Expression_rest → + Term Expression_rest | - Term Expression_rest | nothing
Term → Factor Term_Rest
Term_Rest → * Factor Term_Rest | / Factor Term_Rest | nothing
Factor → Element ^ Factor | - Factor | + Factor | Element
Element → Condition
| ! Element
| built_in ( Expression )
| Function_call ( Argument_list )
| identifier
| Local_id
| number
Condition → ( Formula )
Print_list → Formula , Print_list | Formula | String , Print_list | String
Local_id → $ number
String → " text "
Lvalue → identifier
Procedure_call → identifier
Function_call → identifier
Use `hoc6.pro' for this step. Use `hoc6x.pro' if you want to have a parse tree. For a graphic tree use the aim hoc6g. A file `hoc6.pl' provides a wrapper for swi-prolog system.
Step 7. It should provide new statements (do, for, break, continue, unless, ...), new operators (++, --, +=, /=, ...), local variables (static and automatic), arrays, constants with identifiers, ... It is still not realised. Don't hesitate to make it!
gtree.pro – it is used by the parser graphic tree drawing routine for `hoc1x.pro', `hoc3x.pro', and `hoc5x.pro'.
gtreex.pro – it is used by the parser graphic tree drawing routine for `hoc6x.pro'.
test5.in – a test for `hoc5.pro' and 'hoc5x.pro'.
test6.in – a test for `hoc6.pro' and 'hoc6x.pro'.
www/expr.html – a web interface page for an interactive parse tree generation.
www/expr.sh – a web interface script for an interactive parse tree generation.