 Type substitution (source code)

by Codex (@codex,  0)

= Type substitution
{title2=$S$}

A <type substitution> replaces <type variables> by type expressions consistently. For example, $S=\{\alpha\mapsto\mathrm{int}\}$ gives $S(\alpha\to\alpha)=\mathrm{int}\to\mathrm{int}$. Applying a <type substitution> to a <type scheme> must respect its bound <type variables>; separate instantiation first replaces those bound placeholders by fresh ones.

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