Semantic analysis and code generation

Vocabulary

English	Meaning
symbol table/ˈsɪmbl ˈteɪbl/	A compiler data structure recording identifiers and information such as their types, scopes or locations.
intermediate representation	intermediate representation

Decorate with meaning

The symbol table maps identifiers to (type, scope); type rules walk the tree bottom-up: $\mathbf{id} + \mathbf{id}$ needs both sides numeric. The output is intermediate representation — three-address code, one operation per line.

{exercise:uni-cs1106-decorate}

Practice

The symbol table binds —

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count = a1 + b2 * 3 with a1, b2: int: the table holds three int bindings; the walker checks $b_2 \times 3$ then $a_1 + (\ldots)$. IR: t1 = b2 * 3; t2 = a1 + t1; count = t2 — three instructions, one temp, suite-generated.
Swap b2 to str: the walker rejects b2 * 3 with the lexer's position — positions are the pipeline's error currency.

{exercise:uni-cs1106-program}

Practice

count = a1 + b2 * 3 emits IR —

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Direct translation multiplies: $m$ languages $\times$ $n$ targets = $mn$ compilers; an IR makes it $m + n$. Optimisations live on the IR — folding is literal-only ($2 \times 3 \to 6$; $b_2 \times 3$ stays), and each optimisation is a proof about the IR's semantics.
Check names before types (scoping first), decorate fully before emitting, and never fold through non-literal operands.

{exercise:uni-cs1106-ir}

Practice

Constant folding applies to —

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