GNUmake: how to write a true lambda

Question

The following is my take on a so-so emulation of a lambda expression in GNUmake :

space := $(strip) $(strip)
comma := ,

# convert a space-separated list in $1 into a comma-separated list:
list2param = $(subst $(space),$(comma),$(strip $1))

# param $1 = quoted GUNmake expression
# param $2 = parameters to the expression as space-separated list
lambda = $(eval _lambda=$1)$(eval _lambda:=$$(call _lambda,$(call list2param,$2)))$(_lambda)

Example:

$(info $(call lambda,$$1 .. $$2 .. $$3,foo bar baz))

Output:

foo .. bar .. baz

But this is less than satisfying, as I have to use a variable "_lambda" behind the curtain and the mechanism isn't really like lambda as the evaluation isn't separated from the definition. Is there a clean, direct way to implement a lambda? Or is there already some mechanism implemented which my blind procedural programming eyes didn't catch?

Answer 1

As in any primitive substitution language, you defer evaluation by quoting. The example below looks horrible and doesn't let you nest lambdas, but otherwise works:

define lambda
$(eval lambda-f=$1)lambda-f
endef

$(foreach n,1 2 3,$(call $(call lambda,$$(info $$(shell seq -s ' ' $$1))),$n))

Some readability can be (arguably) regained by amending the syntax like this:

define lambda
$(eval lambda-f=$(subst ^,$$,$1))lambda-f
endef

$(foreach n,1 2 3,$(call $(call lambda,^(info ^(shell seq -s ' ' ^1))),$n))