LIMPid

A simple Language Interpreter of the IMP Language, written in Haskell, for Didactic purposes.

This work is part of the "Formal Methods in Computer Science" exam at University of Bari "Aldo Moro".

Features

LIMPid is an interpreter (with a parser) of an IMP language composed of the following constructs:

• skip performs a jump to the next instruction;
• assignment assigns a value to a variable by calculating it if it is written in the form of an expression;
• If-then-else conditional control structure;
• Do-while iterative control structure of the do-while type;
• While-do iterative control structure of the while-do type;
• For-times iterative control structure of the for type;

LIMPid uses dynamic typization, accepts integer and Boolean data.

Grammar

program ::= <command> | <command> <program>
 
command ::= <skipcommand> | <assignmentcommand> | <ifcommand> | <whilecommand> | <dowhilecommand> | <forcommand>

skipcommand ::= skip <semicolon> 

assignmentcommand ::= <variable> := (<aexp> | <bexp>) <semicolon> | <letter> := { <array> } <semicolon> 

ifcommand ::= if <space> ( <bexp> ) <space> then { <space> (<program> | <program> else { <space> <program>) } <semicolon>

whilecommand ::= while <space> ( <bexp> ) <space> { <space> do <space> <program> <space> } <semicolon>

dowhilecommand ::= do <space> { <space> do <space> <program> <space> } while <space> ( <bexp> ) <space> <semicolon>

forcommand ::= for <space> <variable> <space> times <space> { <space> <program> <space> }
 
array ::= <afactor> | <afactor> <colon> <array>
 
bexp ::= <bterm> | <bterm> <bexpOp> <bexp>
 
bterm ::= <bfactor> | ( <bexp> ) | ! <bexp>
 
bfactor ::= <aexp> | <aexp> <comparisonOp> <aexp> | <variable>
 
aexpr ::= <aterm> | <aterm> <aexpOp1> <aexp>
 
aterm ::= <afactor> | <afactor> <aexpOp2> <aterm>

afactor ::= <apositivefactor> | <anegativefactor> 

anegativefactor ::= - | <apositivefactor> 

apositivefactor ::= <number> | ( <aexp> ) 

number ::= <positivenumber> | <variable> 

positivenumber ::= <digit> | <digit> <positivenumber> 

variable ::= <letter> | <letter> <variabile> |

semicolon ::= ; | ; <space> 

colon ::= , | , <space> 

digit ::= 0-9 

aexpOp1 ::= + | -

aexpOp2 ::= * | / 

bexpOp ::= & | | 

comparisonOp ::= < | > | = | <= | >= | != 

letter ::= a-z 

space ::= " "

How to compile and start

In a Linux-like system, first install Haskell GHC and then

(base) andrea@andrea-N552VX:~/Desktop/LIMPid$ ghci
GHCi, version 8.8.4: https://www.haskell.org/ghc/  :? for help
Prelude> :load LIMPid.hs
[1 of 1] Compiling Main             ( LIMPid.hs, interpreted )
Ok, one module loaded.
*Main> limpid

-+-+-+-+-+- LIMPid Language Interpreter -+-+-+-+-+-

Type ":help" for commands

LIMPid#> TYPE HERE THE CODE TO PARSE AND INTERPRET

Examples of use

Variable assignment and Do-while with nested if-then-else.

LIMPid#>x:=20;
LIMPid#>do { x:=x+1; if (x<30) { y:=x+1; }; }while (x<40) ;
LIMPid#>:printmem

-+-+ Parsed Code +-+-
x:=20;do { x:=x+1; if (x<30) { y:=x+1; }; }while (x<40) ;

-+-+ Memory +-+-
x=>40 y=>30 

Array assignment.

LIMPid#>a:={10,20,30,777};
LIMPid#>:printmem

-+-+ Parsed Code +-+-
a:={10,20,30,777};

-+-+ Memory +-+-
a[0]=>10 a[1]=>20 a[2]=>30 a[3]=>777 

More stuff with arrays:

LIMPid#>index:=0;
LIMPid#>value:=100;
LIMPid#>accumulator:=v[0]+v[1]+v[2];
LIMPid#>:printmem

-+-+ Parsed Code +-+-
v:={1,2,3};index:=0;value:=100;accumulator:=v[0]+v[1]+v[2];

-+-+ Memory +-+-
v[0]=>1 v[1]=>2 v[2]=>3 index=>0 value=>100 accumulator=>6 

Use of the While-do loop.

LIMPid#>x:=0;
LIMPid#>while (x<10) { do x:=x+1; };
LIMPid#>:printmem

-+-+ Parsed Code +-+-
x:=0;while (x<10) { do x:=x+1; };

-+-+ Memory +-+-
x=>10 

Use of the For-times loop.

LIMPid#>x:=5;
LIMPid#>y:=0;
LIMPid#>for x times { y:=y+1; };
LIMPid#>:printmem

-+-+ Parsed Code +-+-
x:=5;y:=0;for x times { y:=y+1; };

-+-+ Memory +-+-
x=>0 y=>5