Semantic Analysis and the Intermediate Representation
Syntactically valid code can fail a language's name, type or argument-count rules. Semantic analysis uses declaration and scope information to check those rules. A shared intermediate representation can connect language front ends to multiple target back ends.
What a learner can do afterwards
- Name three syntactically valid constructs that fail the lesson's static semantic checks
- Explain what a symbol table holds and when it is consulted
- Say why lowering to an intermediate form is worth the extra pass
1 · Read
The parser you studied checks grammatical structure. Here names must resolve to declarations in scope, + requires two numbers without converting strings, and functions have fixed parameter counts. An undeclared name, incompatible operands or an incorrect argument count can have valid syntax but fail semantic analysis. Some compilers combine parsing with semantic checks; we separate their jobs for study.
Suppose paint is declared to take three numbers. paint(2, 4) has valid call syntax but only two arguments. A semantic check compares that count with paint's declaration and reports the mismatch. Type checking is separate: even a three-argument call must supply the required types.
A symbol table records declarations and facts such as kind, type, scope and function parameters. Scope is the region where a declaration is visible. This model adds entries at declarations and consults them at name uses, following scope rules. A declaration elsewhere may not be visible here. The checking code applies the language rules using those entries. Actual table layouts and lookup timing vary between compilers.
An intermediate representation (IR) records program operations in a form shared by compiler stages. Lowering translates a checked tree into IR while preserving meaning. Different language front ends can produce the same IR, and compatible target back ends can consume it. When suitable back ends already exist, a new language can reuse them. This does not guarantee smaller translators or support for every target.
Parsing checks structure. Semantic analysis applies name, type and call rules using declaration information. A shared IR can connect several front ends and back ends.
Lesson, questions and flashcards on semantic analysis and intermediate representations written for this dataset.
2 · Watch
به انگلیسیTake it off screen
Where it sits
Optional connections
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.