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Table Of Contents
Practical Systems Programming in Go
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An evaluator is the component responsible for executing the parsed program. It takes the AST produced by the parser and computes its meaning by walking the tree and performing the operations described by each node. Rather than compiling the program into machine code, the evaluator functions as a tree-walking interpreter, recursively visiting nodes to produce results at runtime. Evaluation begins at the root Program node and proceeds through top-level statements in order. To preserve program state, the evaluator maintains a runtime environment — a map that stores variable bindings as they are introduced. When a variable declaration is encountered, the evaluator first evaluates the associated expression and then stores the resulting value in the environment under the variable's name. Later references to that identifier retrieve the stored value, allowing data to flow across statements and blocks.
Control flow is handled by evaluating conditional expressions. When...