languages in computer science

An English sentence can be regarded as a string of words (단어들의 나열),

and an English word can be regarded as a string of letters (문자들의 나열).

• Not every string of letters is a legitimate (올바른) word, and not every string of words is a grammatical sentence.
• Legitimate word? ⇒ dictionary. Grammar? ⇒ grammar book.

Computer languages are similar to English in that

• Certain strings of characters are legitimate words of the language and
• Certain strings of words can be put together according to certain rules to form syntactically correct programs

A compiler for a computer language analyzes the stream of characters in a program

• First to recognize individual word and sentence units (this part is called a lexical (어휘, 사전적인) scanner),
• Then to analyze the syntax, or grammar, of the sentences (this part is called a syntactic analyzer),
• and finally to translate the sentences into machine code (this part is called a code generator).

Example: a simple calculator language

Words

• Valid: Numbers (123), operators (+, -), and parentheses ((, )).
• Invalid: 12a3, ++.

Sentences

• Valid: 3 + 4, (2 * 5) - 1.
• Invalid: 3 +, 2 * (5 -

Calculator (Compiler) steps