Add typed_function() for runtime-typed function signatures

[Copilot]

sicher had no way to attach type annotations to function parameters or return values — only variables could be typed. This adds typed_function() as the function counterpart to %:% / %<-%.

API

add <- typed_function(
  function(x, y) x + y,
  params  = list(x = Numeric, y = Numeric),
  .return = Numeric
)

add(1, 2)     # → 3
add("a", 2)   # → Error: Type error in 'x': Expected numeric, got string

All existing type constructs work in params and .return:

describe <- typed_function(
  function(id, label = NULL) paste(label, id),
  params  = list(id = String | Numeric, label = Optional(String)),
  .return = String
)

Changes

• R/main.R — typed_function(fn, params = list(), .return = NULL):
  • Validates params entries and .return at construction time
  • Wrapper uses match.call() + eval(parent.frame()) so argument expressions are evaluated in the caller's scope; delegates via do.call(fn, evaled)
  • Default parameter values work naturally — only explicitly supplied args are type-checked
  • Tags wrapper with S3 class sicher_typed_function; stores params / return_type as attributes
• R/main.R — print.sicher_typed_function: renders signature as <typed_function (x: numeric, y: numeric): numeric>
• NAMESPACE — exports typed_function, registers S3 print method
• tests/testthat/test-sicher.R — 8 new tests covering param checks, return type, union/optional params, construction errors, and print output

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[feddelegrand7]

perfekt, now update the readme accordingly and the index.qmd

[feddelegrand7]

update the readme and index.qmd accordingly