app.py

import streamlit as st

# Initial setup for grammar input
rules = []
nonterm_userdef = []
term_userdef = []
diction = {}
firsts = {}
follows = {}
start_symbol = None

# Function to remove left recursion
def removeLeftRecursion(rulesDiction):
    store = {}
    for lhs in rulesDiction:
        alphaRules = []
        betaRules = []
        allrhs = rulesDiction[lhs]
        for subrhs in allrhs:
            if subrhs[0] == lhs:
                alphaRules.append(subrhs[1:])
            else:
                betaRules.append(subrhs)
        if len(alphaRules) != 0:
            lhs_ = lhs + "'"
            while lhs_ in rulesDiction.keys() or lhs_ in store.keys():
                lhs_ += "'"
            for b in range(len(betaRules)):
                betaRules[b].append(lhs_)
            rulesDiction[lhs] = betaRules
            for a in range(len(alphaRules)):
                alphaRules[a].append(lhs_)
            alphaRules.append(['#'])
            store[lhs_] = alphaRules
    for left in store:
        rulesDiction[left] = store[left]
    return rulesDiction

# Function to perform left factoring
def LeftFactoring(rulesDiction):
    newDict = {}
    for lhs in rulesDiction:
        allrhs = rulesDiction[lhs]
        temp = dict()
        for subrhs in allrhs:
            if subrhs[0] not in list(temp.keys()):
                temp[subrhs[0]] = [subrhs]
            else:
                temp[subrhs[0]].append(subrhs)
        new_rule = []
        tempo_dict = {}
        for term_key in temp:
            allStartingWithTermKey = temp[term_key]
            if len(allStartingWithTermKey) > 1:
                lhs_ = lhs + "'"
                while lhs_ in rulesDiction.keys() or lhs_ in tempo_dict.keys():
                    lhs_ += "'"
                new_rule.append([term_key, lhs_])
                ex_rules = []
                for g in temp[term_key]:
                    ex_rules.append(g[1:])
                tempo_dict[lhs_] = ex_rules
            else:
                new_rule.append(allStartingWithTermKey[0])
        newDict[lhs] = new_rule
        for key in tempo_dict:
            newDict[key] = tempo_dict[key]
    return newDict

# Function to calculate FIRST set
def first(rule):
    if len(rule) != 0 and rule[0] in term_userdef:
        return rule[0]
    elif len(rule) != 0 and rule[0] == '#':
        return '#'
    if len(rule) != 0 and rule[0] in diction:
        fres = []
        rhs_rules = diction[rule[0]]
        for itr in rhs_rules:
            indivRes = first(itr)
            if type(indivRes) is list:
                fres.extend(indivRes)
            else:
                fres.append(indivRes)
        if '#' not in fres:
            return fres
        else:
            newList = fres
            fres.remove('#')
            if len(rule) > 1:
                ansNew = first(rule[1:])
                if ansNew is not None:
                    if type(ansNew) is list:
                        newList = fres + ansNew
                    else:
                        newList = fres + [ansNew]
            fres.append('#')
            return fres

# Function to calculate FOLLOW set
def follow(nt):
    solset = set()
    if nt == start_symbol:
        solset.add('$')
    for curNT in diction:
        rhs = diction[curNT]
        for subrule in rhs:
            if nt in subrule:
                while nt in subrule:
                    index_nt = subrule.index(nt)
                    subrule = subrule[index_nt + 1:]
                    if len(subrule) != 0:
                        res = first(subrule)
                        if res is not None:
                            if '#' in res:
                                res.remove('#')
                                follow_res = follow(curNT)
                                if follow_res:
                                    res += follow_res
                        else:
                            res = []
                    else:
                        if nt != curNT:
                            res = follow(curNT)
                            if res is None:
                                res = []
                    solset.update(res if type(res) is list else [res])
    return list(solset)

# Compute FIRST for all non-terminals
def computeAllFirsts():
    global firsts
    for y in diction.keys():
        firsts[y] = set()
        for sub in diction[y]:
            result = first(sub)
            if result is not None:
                firsts[y].update(result if type(result) is list else [result])

# Compute FOLLOW for all non-terminals
def computeAllFollows():
    global follows
    for NT in diction.keys():
        follows[NT] = set(follow(NT))

# Parse table creation function
def createParseTable():
    global term_userdef, firsts, follows
    table = {}
    grammar_is_LL = True
    for lhs in diction.keys():
        table[lhs] = {}
        for term in term_userdef + ['$']:
            table[lhs][term] = ""
    for lhs in diction:
        for rule in diction[lhs]:
            first_res = first(rule)
            if '#' in first_res:
                first_res.remove('#')
                follow_res = follows[lhs]
                first_res.update(follow_res)
            for term in first_res:
                if table[lhs][term] == "":
                    table[lhs][term] = f"{lhs} -> {' '.join(rule)}"
                else:
                    grammar_is_LL = False
    return table, grammar_is_LL

# Validate input string function
def validateStringUsingStackBuffer(parse_table, input_string):
    stack = [start_symbol, '$']
    buffer = ['$'] + input_string.split()[::-1]
    while stack:
        top_stack = stack.pop(0)
        top_buffer = buffer.pop()
        if top_stack in term_userdef:
            if top_stack != top_buffer:
                return "Invalid String"
        elif top_stack == top_buffer:
            continue
        else:
            rule = parse_table.get(top_stack, {}).get(top_buffer, None)
            if rule:
                rule_rhs = rule.split('->')[1].strip().split()
                stack = rule_rhs + stack
            else:
                return "Invalid String"
    return "Valid String"

# Streamlit Interface
st.title("LL(1) Grammar Analyzer")

st.subheader("Grammar Rules Input")
start_symbol = st.text_input("Enter Start Symbol (Non-terminal)")
num_rules = st.number_input("Number of Grammar Rules", min_value=1, step=1)
rules = []
for i in range(num_rules):
    rule = st.text_input(f"Rule {i+1}")
    if rule:
        rules.append(rule)

nonterm_userdef = st.text_input("Enter Non-Terminals (comma-separated)").split(',')
term_userdef = st.text_input("Enter Terminals (comma-separated)").split(',')

if st.button("Analyze Grammar"):
    diction.clear()
    firsts.clear()
    follows.clear()

    for rule in rules:
        lhs, rhs = rule.split("->")
        lhs = lhs.strip()
        rhs_list = [x.strip().split() for x in rhs.split("|")]
        diction[lhs] = rhs_list

    st.subheader("Grammar After Removing Left Recursion")
    diction = removeLeftRecursion(diction)
    st.write(diction)

    st.subheader("Grammar After Left Factoring")
    diction = LeftFactoring(diction)
    st.write(diction)

    computeAllFirsts()
    st.subheader("FIRST Sets")
    st.write(firsts)

    computeAllFollows()
    st.subheader("FOLLOW Sets")
    st.write(follows)

    parse_table, grammar_is_LL = createParseTable()
    st.subheader("Parse Table")
    st.write(parse_table)

    if grammar_is_LL:
        st.success("The grammar is LL(1)")
    else:
        st.error("The grammar is not LL(1)")

    input_string = st.text_input("Enter String to Validate (space-separated)")
    if input_string:
        result = validateStringUsingStackBuffer(parse_table, input_string)
        st.subheader("Validation Result")
        st.write(result)