31 lines
1.6 KiB
Markdown
31 lines
1.6 KiB
Markdown
# Compilers - COMP 3012
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A compiler is a tool that maps one language into another language. It takes a program written in a source programming language and maps it to a program written in a target programming language. A compiler is written in an **implementation language**.
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Notation of semantics of program $A$: $[\![A]\!]$
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An **interpreter** is a program that takes a source program and executes the program.
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> NOTE: Java uses both. A Java source program is compiled into bytecode (by a compiler), which is then executed by an interpreter (called the Java virtual machine - JVM). The JVM will also compile fragments of code so that if there is a call back, it can execute the compiled code. This is called compilation on the fly.
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Compilers will often use an **intermediate representation (IR)** to bridge the gap between the source language and the executable language. Converting source language to IR is called **front end**, whereas converting IR to executable code is called **back end**.
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- The front end focuses on understanding the source-language program.
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- The back end focuses on mapping programs to the target machine
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- The front end, intermediate representation and the back end are all part of the compiler.
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IR is stored as an Abstract Syntax Tree **AST**.
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The syntactic details needed for parsing the source program are represented in the structure of the tree.
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The **IR** could be broken down into many sub-steps, i.e. an IR1 could be created, which is then run through an optimiser to create IR2, which is fed into the back end instead of IR1. This is called a *three-phase compiler*.
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