Lecture 05: Lexical Analysis – Deterministic Finite Automaton

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what are the responsibilities of the lexical analyser
öğrenmeye başla
[1] tokenizing source [2] removing comments [3] saving text of identifiers, numbers, strings [4] saving source locations (file, line, column) for error messages
whata re the 3 ways to build a lexical analyser
öğrenmeye başla
(1) Write a formal description (e.g., REs) of the token patterns, a Design a state transition diagram (DFA) that describes the token patterns and (2) write a program to implement the diagram, or (3) write a table-driven implementation of DFA.
Whata re state transition diagrams?
öğrenmeye başla
directed graphs, are representation of mathematical “machines” called finite state automata (FSA) or just finite automata (FA).
Finite automata could be _____(DFA) or ______(NFA).
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Finite automata could be deterministic (DFA) or nondeterministic (NFA).
when is FA determanistic?
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A FA is deterministic if it performs the same operation (state transition) in a given situation (its current state and input).
when is fa nondeterministic
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A FA is nondeterministic if it can perform any of a set of state transitions in a given situation.
what are the properties of a finite state automaton (FSA), or simply finite automaton
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[1] read in' str' from L-R, 1 sym' at a time[2] in 1 of a finite No. ofState[3]4 each sym' it moves to a new state determined by its current state&the sym' read[4] str' is acptd or rejcted depending on the state of the machine after read the final sym'
what is the formal deffinition of finite automation (FA) M
öğrenmeye başla
finite set Q of states, finite alphabet Σ of input symbols, distinguished start state q1 ∈ Q, set of final states F ⊆ Q, and transition function δ: Q × Σ → Q that chooses a new state for M based on the current state, Q, and the current input symbol, Σ
what is DFA for Lexical Analysis
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As far as lexical analysis is concerned, a DFA is a string processing machine
what does DFA do for Lexical Analysis
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fuck you
what is The set of all strings accepted by a DFA known as
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language recognised
how are DFA digrams simplified?
öğrenmeye başla
Similar to the case of REs, we name a set of symbols letter = {a, b, c,..., z, A, B, C,..., Z} digit = {0,...,9} and replace their arcs by a single arc labelled letter Or digit (or simply d as in our example)

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